Bio Slides PDF

Identifying, Classifying & Naming Agenda 1. Questions about the course? 2. Bacteria cultures check 3. Hierarchical Classiﬁcation 4. Binomial Nomenclature 5. Classwork/Homework Part A: Group Activity 1. Take a look at each organism in front of you. 2. With your partners, discuss the best way to separate the organisms into groups. 3. Identify the groups with a category. Part B: Discussion Questions 1. On what basis did you initially separate your organisms? 2. After the initial grouping, what characteristics did you use as distinguishing factors? Which one of these is not like the others? Which one of these is not like the others? Which one of these is not like the others? The Six Kingdoms Organisms are organized according to cell type, ability to make food, and number of cells Terminology Cell type prokaryotic – no nucleus, no membrane bound organelles, DNA is circular (plasmid), smaller eukaryotic – have a nucleus and membrane bound organelles, DNA in chromosomes, larger Terminology Getting food Body type Reproduction autotrophs – unicellular – sexual – need make their own made of only male and female food (ex. plants) one cell parents heterotrophs – multicellular – asexual – need get their food made of more only one parent from other than one cell; sources (ex. cells have people) specialized functions A Typical Bacteria Cell Archaebacteria - ”ancient bacteria” (existed before dinosaurs) - live in extreme environments - hot springs - acidic environment - methane rich environment - unicellular prokaryotes - some autotrophs , some heterotrophs Eubacteria - The chemical makeup of eubacteria is different from that of archaebacteria and they do not live in extreme environments. - unicellular prokaryotes - some autotrophs , some heterotrophs Protists - “odds and ends” kingdom because its organisms are pretty different from one another - eukaryotes that aren’t plants, animals, or fungus - most unicellular , some multicellular - some autotrophs , some heterotrophs A Typical Protist Fungi - ex. mushrooms, mold, mildew, some skin infections - most are multicellular , some (like yeast) are unicellular - eukaryotes - all are heterotrophs - eat dead or decaying organisms World’s Largest Organism It’s a fungus. It lives in the Blue Mountains of Oregon (USA), and it makes the blue whale look like an insect. The Armillaria ostoyae specimen takes up over 2,000 acres. A Typical Fungal Cell Plants - all plants are multicellular - all are eukaryotes - plants are autotrophs Typical Plant Cell Animals -all are multicellular -all are eukaryotes -all are heterotrophs Typical Animal Cell The Six Kingdoms Review Eubacteria – “true” bacteria (prokaryotic) Archaebacteria – “ancient” bacteria (prokaryotic) Protista – WEIRD organisms!!!! (eukaryotic) Fungi – digest dead or decaying matter (eukaryotic) Plantae – stationary, photosynthetic (eukaryotic) Animalia – mobile heterotrophs (eukaryotic) Different cells from different Kingdoms: - You do NOT have to label all the parts of the different cells - You do have to be able to distinguish between the different cell types and provide similarities and differences between them Taxonomy Branch of biology that identiﬁes, names and groups organisms according to their characteristics and evolutionary history Hierarchical Classiﬁcation A system of rank (levels) that organize species into broad groups and further organizes them into more speciﬁc groups. Each group is called a Taxon. Taxonomic Ranks Domain Kingdom Phylum Class Order Family Genus Species Mnemonic Device King Phillip Came Over From Greater Spain King Pang Cooks Organs For Greedy Students Kings Play Chess On Fine Grain Sand Examples FYI: How is the name of an organism decided? Carl Linnaeus - Performed careful observations on organisms’ physical features - Developed a system of naming organisms called: binomial nomenclature - Published classiﬁcations in a book called Systema Naturae Binomial Nomenclature Binomial = “Two Terms” Nomenclature = “System of names” Binomial Nomenclature First Word: GENUS (2nd most speciﬁc taxonomic rank) This word is Capitalized & Italicized when typed. Second Word: SPECIES (most speciﬁc taxonomic rank) This word is lowercase & Italicized when typed. *** When written, both words are underlined*** Weird Scientiﬁc Names?! Challenge: Find the weirdest scientiﬁc name for an organism. We will compare! Summary of 6 Kingdoms (If you need) Summary of Classiﬁcation (If you need) Intro to Biodiversity Review 1. Explain why some species must be deﬁned based on their morphology rather than on reproductive behaviour 2. What is a consequence of losing biodiversity? Taxonomy Create a Classiﬁcation System Classify the following domesticated species into at least 3 categories: Corn Cats Spider Plants Button Mushrooms Goats Llamas Lettuce Basil Koi Fish Create a Classiﬁcation System What categories did you use? Why? Were there any challenges in deciding on categories? Why? Do you think there might be one “best” classiﬁcation system? Explain. Why Classify? Taxonomy is the study of identifying and classifying organisms. It allows for: Convenient retrieval of information Tools for communication Ease in seeing the relationships between organisms Carol von Linné Carolus Linnaeus - the “father” of taxonomy Swedish scientist credited with the Linnaean System of naming organisms still used today Used binomial nomenclature (2 names) - ex. Homo sapiens Grouped organisms by structural similarities - other groupings at the time were more arbitrary Taxonomy The ﬁrst part of the name refers to the genus: a small group of related species ○ The genus is always capitalized The second part is the species name ○ The species name is written in lower case Names written in binomial nomenclature are italicized if typed or underlined if hand written ○ Ex. E. coli or Escherichia coli Linnaeus then created subsequent grouping levels based on similarities Taxonomic Levels Linnaeus grouped species into taxonomic ranks or levels based on shared characteristics Each level is called a taxon Similar species grouped into a genre Similar genre into families Similar families into orders Similar orders into classes Similar classes into phyla Similar phyla into kingdoms Similar kingdoms into domains Taxonomic Levels Each taxonomic rank consists of species that have similar features ○ Ex. all species in the phylum Chordata have a backbone or primitive backbone ○ Ex. all members of the class Mammalia are warm-blooded and feed milk to their young Modern taxonomists have created intermediate taxonomic levels (ex. Superorders, subfamilies) to help classify the many new species we have discovered Common Human Gorilla Canada Frog Mosquito name goose Kingdom Animalia Animalia Animalia Animalia Animalia Phylum Chordata Chordata Chordata Chordata Arthropoda Class Mammalia Mammalia Aves Amphibia Insecta Order Primates Primates Anseriformes Lissamphibia Diptera Family Hominidae Hominidae Anatidae Anura Culicidae Genus Homo Gorilla Branta Litoria Aedes Species sapiens gorilla canadensis caerulea fitchii Kingdoms and Domains Early classiﬁcation only recognized two kingdoms of living things - Animals and Plants The discovery of microorganisms changed our understanding of living things ○ Biologists discovered prokaryotes - unicellular organisms that do not have membrane-bound organelles (ex. bacteria) ○ They also discovered new eukaryotes - Protists - unicellular and smaller multicellular organisms with organelles Dichotomous Key Scientiﬁc tool, used to identify 1a. Vegetable - 2 different organisms, based on 1b. Fruit - 3 their observable traits 2a. Green vegetable - spinach Dichotomous keys consist of a 2b. Yellow vegetable - squash series of paired statements or 3a. Red fruit - 4 couplets Each statement leads to 3b. Yellow fruit - lemon another series of paired 4a. Hard ﬂesh - apple statements or a name 4b. Soft ﬂesh - cherry Kingdoms and Domains In 1996, Carl Wose organized all organisms into three distinct groups (domains) - Bacteria, Archaea & Eukarya Domain Bacteria contains only the kingdom Eubacteria Domain Archaea contains only the kingdom Archaebacteria Domain Eukarya contains the other 4 kingdoms: Animalia, Plantae, Fungi & Protista Domain Kingdom Characteristics Examples Bacteria Eubacteria Prokaryotic, No nucleus, Reproduce asexually E. Coli Archaea Archaebacteria Prokaryotic, Live in extreme conditions, Halophiles, Reproduce asexually Thermophiles Animalia Eukaryotic, Multi-cellular, Heterotrophic, Can Dogs, Humans move independently Plantae Eukaryotic, Multicellular, Autotrophic, Cells Oak tree contain cell wall and chlorophyll Eukarya Fungi Eukaryotic, Multicellular, Heterotrophic, No Mushrooms chlorophyll, Cells contain cell wall without cellulose Protista Eukaryotic, Uni or multicellular, Both hetero and Algae, autotrophs, May contain chlorophyll, Simple Amoeba cellular organization Creating a Dichotomous Key Consider one characteristic at a time ○ 1a. Spots ○ 1b. No spots Vs. ○ 1a. Spots ○ 1b. Four legs All statements should be paired Use deﬁnitive and contrasting statements Use observable traits Do not use vague terms (big, smaller, medium etc.) You should ﬁnish with one less step than the number of organisms you are organizing If you are organizing 6 organisms, you should have 5 steps Creating a Dichotomous Key Create a Dichotomous Key using the species from the beginning of the lesson Corn Cats Spider Plants Button Mushrooms Goats Llamas Lettuce Basil Koi Fish Phylogeny Family Tree Draw your family tree, include aunts, uncles and cousins Who is a common ancestor of both you and your 1st cousin? How can you tell who is more closely related to who? A Shift in Philosophy In 1859, Charles Darwin published On the Origin of Species, which revolutionized how scientists thought about species He proposed that species branched from a common ancestor Therefore, species could be classiﬁed based on their evolutionary relatedness and not just on their morphology Phylogeny Taxonomists looked to incorporate our newer understanding of common ancestors Phylogeny - the study of the evolutionary relatedness between, and among, species Phylogenetic tree - a diagram depicting the evolutionary relationships between different species or groups Phylogenetic Tree Who is more closely related to green alga; red alga or pine? Clades In phylogenetic trees, species are grouped into clades Clade - taxonomic group that includes a single common ancestor and all its descendants (living and extinct) Taxonomy Today Advantage to phylogeny - shows relatedness of organisms even though they may not look similar ○ Ex. Crocodiles are more closely related to birds than to snakes Disadvantages - in order to build a correct phylogenetic tree, a large amount of DNA (genetic) and fossil record research must be done Cladograms Diagrams depicting the relationship between different clades by grouping organisms together based on their shared derived characteristics Cladograms illustrate relationships between species based on traits - do not necessarily describe the process of evolution or amount of difference between groups Name all of the organisms with a vertebrae Name all the organisms with four limbs, and hair Name all the organisms with a bony skeleton that do not have four limbs Build a cladogram using the table of species and derived characteristics below Prokaryotes How many bacteria species reside in your mouth? a. 10 b. 50 c. 500 d. 700 e. 1000 How many bacteria species reside in your mouth? a. 10 b. 50 c. 500 d. 700 e. 1000 In ideal conditions, bacteria can reproduce every: a. Minute b. 5 minutes c. 20 minutes d. Hour e. Day In ideal conditions, bacteria can reproduce every: a. Minute b. 5 minutes c. 20 minutes d. Hour e. Day If there were enough space and resources to reproduce, one bacteria, in a day, could form a ball the size of: a. A pill b. A sugar cube c. An apple d. A softball If there were enough space and resources to reproduce, one bacteria, in a day, could form a ball the size of: a. A pill b. A sugar cube c. An apple d. A softball If there were enough space and resources to reproduce, one bacteria, in a week, could form a ball the size of: a. A basketball b. A car c. Ontario d. North America e. Earth If there were enough space and resources to reproduce, one bacteria, in a week, could form a ball the size of: a. A basketball b. A car c. Ontario d. North America e. Earth How many bacteria would ﬁt across the dot of an “i” at 12 point font? a. 200-300 b. 400-500 c. 500-1000 d. 1000-1500 e. 1500-2000 How many bacteria would ﬁt across the dot of an “i” at 12 point font? a. 200-300 b. 400-500 c. 500-1000 d. 1000-1500 e. 1500-2000 Prokaryotes Domain Eubacteria (bacteria) and Domain Archaea (archaebacteria) are prokaryotes Single-celled organisms Lack membrane-bound organelles Lack a nucleus Smallest organisms on Earth Most numerous organism on Earth ○ 39 trillion bacteria on or within your body vs 30 trillion human cells ○ Total mass exceeds that of all animals on Earth Importance of Prokaryotes Negatives (to humans) Infectious bacteria (pathogens) responsible for many human deaths Bacteria infect livestock and crops Importance of Prokaryotes Positives Play key roles in ecosystems - as decomposers or producers, recycle nutrients, vital to biogeochemical cycles Major producers in marine ecosystems - produce atmospheric oxygen Important residents in animal intestines - we rely on bacteria to produce vitamins K and B12 Essential in the production of foods such as cheeses, yogurt, soy sauce and chocolate Produce natural antibiotics Produce valuable compounds such as insulin and human growth hormone Domain Archaea Little known about archaea Genetically distinct from bacteria and eukaryotes Methanogens - live in low oxygen environments, convert chemical compounds into methane Halophiles - live in highly saline environments such as preserved foods and the Dead Sea Extreme Thermophiles - live in extremely hot environments (70-90 degrees C) such as hot springs and hydrothermal vents on the ocean ﬂoor Psychrophiles - live in extremely cold conditions (-10 to -20 degrees C) such as the Arctic and Antarctic oceans Domain Eubacteria Prokaryotes have lived on Earth for more than 3.5 billion years Genetic studies suggest this domain diversiﬁed early Contain bacterias we are most familiar with Bacterial Structure Pili or Fimbriae- hair like structures, help bacteria attach to other cells and surfaces Cell Wall ○ Outer capsule, outer membrane, peptidoglycan layer Plasma Membrane (cytoplasmic membrane) Bacterial Structure Flagella (or ﬂagellum) - used for movement Chromosome - single loop of DNA found in region called the nucleoid Plasmids - small loops of DNA Cell Wall Some bacteria are surrounded by a sticky capsule ○ Reduces water loss, resists high temperature,and helps keep out antibiotics and viruses Bacterial cell walls are composed of peptidoglycan - large molecule (amino acids and sugars) that forms long chains Gram Positive - appear purple/violet when stained ○ Lots of peptidoglycan Gram Negative - appear pink when stained ○ Less peptidoglycan with an additional outer membrane ○ More resistant to antibiotics than gram-positive bacteria Shapes 3 common shapes Coccus - round Bacillus - rod-shaped Spirillum - spiral or corkscrew Arrangements 3 common arrangements - use preﬁxes to indicate arrangements Diplo - pairs Staphylo - clumps Strepto - strings Diplococcus Staphylococcus Streptococcus Structure, Shape & Arrangement Review Metabolism Wide variety of ways that bacteria acquire nutrients and energy Autotrophs - assemble complex carbon molecules from inorganic chemicals (abiotic origin) ○ Photoautotrophs - photosynthesize ○ Chemoautotrophs - use hydrogen, sulfur, or iron compounds for energy Heterotrophs - get nutrients from carbon containing organic chemicals (found in living organisms or their remains) Metabolism Metabolism using oxygen - aerobic cellular respiration Metabolism not using oxygen - anaerobic fermentation Bacteria can be: Facultative Obligate Aerobe Can perform respiration Cannot survive without with or without oxygen oxygen Anaerobe Can perform respiration Cannot survive in the with or without oxygen presence of oxygen Reproduction Reproduce by binary ﬁssion - cell copies its DNA, then splits in half resulting in two daughter cells (asexual reproduction) Incredibly fast reproduction rate - every 4 to 20 minutes - a single bacteria can become billions in 24 hours Errors when copying result in mutations - change the genetic makeup of the cell Because of the rapid reproduction rate of bacteria, they can mutate 1000 times as often as eukaryotic genes These mutations increase the genetic diversity of bacteria populations Reproduction Conjugation - one bacterial cell passes a copy of a plasmid to a nearby cell through a pilus ○ Considered sexual reproduction because two different cells are sharing genetic information Transformation - when cells pick up loose fragments of DNA from the environment ○ Horizontal DNA transfer - transformation of DNA from a different species Bacterial Diseases Some bacteria cause disease by producing toxins ○ For example Clostridium botulinum grows in poorly preserved foods ○ Its toxin, botulin, is so powerful that one teaspoon could kill 1.2 billion people ○ We also use it for botox (concentrations are not toxic and it is injected into the muscle) Some bacteria release toxic compounds when the cell dies ○ For example E.coli may release a dangerous amount of toxins if antibiotics are administered in too high of a dose Human Bacterial Diseases Cholera - Vibrio cholerae - watery diarrhea, vomiting, muscle cramps Diphtheria - Corynebacterium diphtheriae - sore throat, fever, barky cough Lyme disease - Borrelia burgdorferi - spread by ticks, paralysis of the face, joint pain, severe headaches with neck stiffness Pertussis - Bordetella pertussis - whooping cough, fainting, vomiting Human Bacterial Diseases Rocky Mountain spotted fever - Rickettsia rickettsii - contracted from ticks, fever, nausea, rash ○ Fatality rate before antibiotics was 30% - now it is 1% Scarlet fever - Streptococcus pyogenes - (same as strep throat), sore throat, fever, rash Tetanus - Clostridium tetani - lockjaw, muscle spasms and contractions, broken bones, death (10%) Life Before Antibiotics King Alexander of Greece was bitten by a monkey and died from the infection in 1920 90% of children who contracted meningitis died (now 10-15%) Before penicillin, you could die from an infected cut Pneumonia, gonorrhea, and strep throat were incurable Alexander Fleming 1928 - when returning from vacation, he was sorting through bacterial plates Found that one culture was contaminated by a fungus and that the bacterial colonies surrounding the fungus had been destroyed The mold was identiﬁed as being from the genus Penicillium Hence the discovery of penicillin which inhibits the growth of bacteria Antibiotic Resistance Overuse of antibiotics is producing antibiotic resistant bacteria Doses of antibiotics will kill non-resistant bacteria, but resistant bacteria will survive Resistant bacteria are a result of mutations that occurred prior to antibiotic exposure - not a mutation in response to the antibiotics Surviving bacteria (resistant population) will reproduce and the next generation will be made up of more antibiotic resistant bacteria Overuse of Antibiotics Other issues include the killing of useful bacteria Decreased effectiveness of antibiotics - create resistant strains of bacteria Viruses Characteristics Very small, non-living particles Consist of a protein capsid surrounding genetic information (DNA or RNA) ○ Some viruses are surrounded by an envelope, created when a virus leaves a host cell and the host cell membrane wraps around the virus Characteristics All viruses are infectious - passed from cell to cell and organism to organism ○ When a virus enters a host cell, the viral DNA or RNA may begin to take control of the cell ○ The cell eventually makes copies of the virus Importance of Viruses Responsible for many human diseases ○ Range from mild (common cold, chicken pox) to serious and deadly (AIDS, cholera, rabies) Signiﬁcant because of their ability to spread quickly ○ Epidemic - outbreak of disease in a particular region ○ Pandemic - epidemic on a global scale Importance of Viruses Some viruses play a role in cancers - viruses infect host cells and mutate host DNA ○ Hepatitis C shown to contribute to liver cancer Viruses also cause diseases in plants and animals Play an important role in ecosystems - controlling populations Classiﬁcation Though classiﬁed as non-living, viruses reproduce ○ However, they cannot reproduce without a host cell Classiﬁed based on shape, size, and genetic material into orders, families, genre, and species Classiﬁcation Usually infect a speciﬁc type of cell in a host ○ Ex. cold virus infects upper respiratory tract cells Some can infect many different species ○ Ex. Rabies Bacteriophages Viruses that infect bacteria are called bacteriophages (phages) Bacteriophages inject their DNA into the bacterial cell while the protein capsule remains outside the cell Most of our early understanding of viruses came from researching bacteriophages Infectious Cycles Viruses can only become active when they have entered and taken control of a living cell Process of infecting, replicating, and destroying a host cell is called an infectious cycle Infectious Cycles Lysogenic cycle ○ Viral DNA in dormant state - lysogeny ○ Viral DNA inserts itself into host chromosome ○ As host cell grows and divides, it copies viral DNA ○ Change to cell’s environment (often a stressor) triggers viral DNA to become active and enter the lytic cycle Infectious Cycles Lytic cycle ○ Viral DNA separates from host chromosome and instructs the cell to make and assemble new viral DNA and capsids ○ Once assembly of 100-200 new viruses is complete the host cell ruptures - lysis - releasing new viruses Vaccines Vaccines are weakened forms or parts of a dangerous virus When injected into an individual’s body, they trigger an immune response without causing infection The immune system will build a “memory” of the virus, allowing it to respond quickly if it ever encounters it in the future Vaccines Vaccination programs have saved countless lives, reduced suffering, and helped to eradicate many serious diseases ○ Last known natural case of smallpox - 1977 ○ Vaccine for HPV (human papillomavirus) - which is responsible for 70% of all cancers of the cervix - is 99% effective at preventing the spread of the virus A new type of vaccine - mRNA vaccines ○ Another explanation Challenges in Developing Vaccines For some diseases (ex. inﬂuenza) - the virus is constantly changing ○ Vaccines that work against a form of the disease one year are unlikely to be as effective the following year For other diseases - such as HIV/AIDS - the structure and characteristics of the infection are obstacles to vaccine development HIV HIV is a retrovirus - contains RNA and a protein to create DNA inside the host cell The viral DNA integrates into the host cell’s DNA Large numbers of virus copies are made and released HIV attacks white blood cells that ﬁght infections (CD4+ T-cells) HIV HIV has a high rate of copying (10^10 per day) that mutations occur very frequently The body’s immune system can’t respond effectively because: ○ It is being attacked ○ It can’t recognize and ﬁght infected cells quickly enough HIV Vaccine Controversy The Lancet Article - 1998 - AJ Wakeﬁeld - REDACTED Found that the study was based on data from 12 subjects that had been recruited selectively from an anti-vaccine group Data had been altered Wakeﬁeld was being paid by a group that had launched a lawsuit against the makers of the MMR vaccine Vaccine Controversy Response from scientiﬁc community Lancet Article - 1999 - “...no epidemiological evidence for causal association” Studies by the Centers of Disease Control and Prevention, the American Academy of Pediatrics, US National Academy of Sciences, and the UK National Health Service have failed to ﬁnd a link The incident of scientiﬁc dishonesty has been called ‘the most damaging medical hoax of the past 100 years’ Vaccine Controversy Why would people believe that autism and vaccines are related? What types of biases are there? Why might people believe autism and vaccines are related? Why is understanding bias important? Herd Immunity Indirect protection from an infectious disease When a substantial proportion of the population is immune to a virus, it limits the ability of the virus to spread in that population The percentage of people who need to be immune to achieve herd immunity varies with each disease ○ Measles requires 95% vaccination rate ○ Polio requires 80% vaccination rate Gene Therapy Using the mechanism of viruses to treat diseases Use virus capsules to deliver drugs to targeted cells (ex. Deliver chemotherapy drugs to cancer cells) Use viruses to insert new copies of a gene (ex. To correct genes that cause genetic disorders) Use viruses to insert a gene from one species to another (ex. GMOs or genetic engineering of plants) Prions Abnormally shaped proteins that cause disease (all affect brain and nervous tissue) Abnormal protein interacts with normal neural proteins and change their shape Result in cell death and “spongy holes” in the brain The Nature of Heredity Traits What traits in humans are variable? What features have you inherited from your parents? Heredity Cell Division is used for growth and repair in multicellular organisms and reproduction in unicellular organisms Key feature of cell division and reproduction is the passing of chromosomes from the parent cell to the daughter cell - chromosomes carry information for traits Heredity - the passing of traits from parents to offspring Genetic Material Material in an organism that stores genetic information Contained in a molecule of DNA (deoxyribonucleic acid) Genetic Material All living things contain DNA DNA from every organism looks essentially the same Genetic Material DNA contains all the information necessary to make a complete organisms DNA encodes the information Allows for stable storage and reliable replication Genes DNA is organized into genes ○ Distinct sequences of genetic information Cells decode the information in genes to build proteins Each protein carries out a unique function Genes Genes can be turned “on” and “off” All cells within and individual contain the exact same genetic information Different sets of genes are turned “on” in different types of cells “Now there are so many people in the world that the system is repeating itself.” DR. MANEL ESTELLER, who led a genetic study on people who look alike but are not related. Trilobites Your Doppelgänger Is Out There and You Probably Share DNA With Them That person who looks just like you is not your twin, but if scientists compared your genomes, they might find a lot in common. Locus Each gene occupies a speciﬁc location or locus (plural is loci) on a chromosome A typical chromosome carries information for hundreds of thousands of different genes Nucleotides DNA is made up of four building blocks (nitrogenous bases) Adenine, Thymine, Cytosine, Guanine The building blocks of DNA are arranged into very long strands Nucleotides The order of nucleotides in a DNA strand is called a sequence Nucleotides form base pairs ○ Adenine with Thymine ○ Cytosine with Guanine DNA Structure One nucleotide is composed of: ○ One phosphate group ○ One 5 carbon sugar ○ One nitrogenous base The “backbone” is sugar and phosphate and the “rungs” are the bases forming a “Double Stranded Helix” Sequences The human genome contains about 3 billion nucleotides Each individual has a unique DNA sequence Differences in DNA sequences can translate to differences in protein function Reproduction Asexual reproduction A new individual produced from a single parent by cell division Genetic makeup of the offspring is identical to the parent Advantages: do not need to seek out a mate, perform mating behaviors or possess specialized anatomy Reproduction results in heredity that is direct and invariable Reproduction Sexual reproduction Offspring produced from fusion of two sex cells Resulting in genetic makeup that is different from that of either parent Disadvantages: requires specialized organs, mating behaviors, biologically costly (develop traits) and potentially risky (attention seeking traits or behaviours), may create a combination that results in weak offspring Advantages: genetic variation, adaptation to changing environments Meiosis Introduction to Meiosis Mitosis ensures the genetic continuity of cells within any multicellular organism ○ The speciﬁc chromosome number is maintained When gametes (sex cells) unite in sexual reproduction, both cells have half sets of chromosomes ○ Otherwise, each new generation would have double the number of chromosomes Meiosis prevents doubling from occurring Chromosome Number and Structure Human somatic cells contain 46 chromosomes ○ This is termed the diploid number (2n) These are arranged in 23 pairs of homologous chromosomes ○ One from the mother (maternal set) ○ One from the father (paternal set) The Human Cycle The process of meiosis produces gametes (ova and sperm) that contain one of each of the homologous pairs of chromosomes This is called the haploid number (n) ○ In humans, n=23 Where does this occur? In humans: Sperm cells are produced by spermatogonia in the male testes Eggs are produced by the oogonia in the female ovaries In plants: Pollen and ovules are produced Meiosis I Interphase DNA has duplicated Similar to mitosis where the chromosomes replicated prior to prophase Total number of chromatids = 92 Prophase I Homologous chromosomes link as they condense forming tetrads Crossing over occurs Crossing Over Exchange of parts of non-sister chromatids ○ Duplicated maternal and paternal chromosomes ○ Tetrads Results in reformed sister chromatids 1st important source of genetic variation Metaphase I Microtubules move homologous chromosomes to metaphase plate Random assortment occurs Random Assortment Random alignment of maternal and paternal chromosomes at the metaphase plate There are numerous possible combinations of chromosomes ○ 223 = 8,388,608 possible combinations 2nd important source of genetic variation Anaphase I Microtubules separate homologous chromosomes Sister chromatids remain together Telophase I Two haploid daughter cells form from cytokinesis Meiosis II Prophase II A new set of spindle ﬁbres form and the chromosomes begin to move toward the equator of the cell Total chromatids is 46, although this is haploid because there are 23 chromosomes Metaphase II Sister chromatids line up at new metaphase plate Anaphase II Sister chromatids separate Telophase II Four haploid cells result Sperm Cells At the end of meiosis in males four functional cells are produced called spermatids These undergo differentiation to become sperm cells ○ Head - contains the nucleus ○ Tail - ﬂagellum for movement ○ Midsection - contains mitochondria (energy) Egg Cells Meiosis I - the division of cytoplasm is unequal producing one large cell containing nearly all the nutrients (Secondary Oocyte) and one small cell (1st polar body) Meiosis II - the secondary Oocyte divides unequally again producing one large ovum (egg) and a 2nd polar body ○ The 1st polar body may divide, but usually deteriorates Mistakes in Meiosis Aneuploidy Too many or too few chromosomes Results from nondisjunction - when homologous chromosomes fail to separate during meiosis Trisomy - 3 copies of one chromosome Monosomy - one chromosome in place of a homologous pair Common Nondisjunction Disorders Duplications or Deletions Chromosomes exchange information incorrectly during the crossing over process Have the correct number of chromosomes, but the genetic information is altered Translocation Transfer a piece of one chromosome to a nonhomologous chromosome ○ Ex. Burkitt’s Lymphoma Mitosis vs Meiosis Mitosis - essential for the development and maintenance of each individual Meiosis - essential for gamete production and the continuation of the species into the next generation Karyotyping & Sex Determination Karyotypes During mitosis, cell division can be stopped, stained, and photographed under a microscope to create a karyotype Karyotype - a picture of chromosomes that have been arranged according to number, size, shape, or some other characteristic Allows scientists to count and compare chromosomes Diagnosis Karyotyping is done during genetic screening Cells are gathered from amniotic ﬂuid, bone, bone marrow, or placenta Cells are stopped in mitosis - metaphase is ideal Turner’s Syndrome (45, X) Edward’s Syndrome (47, XY, +18) Typical Female (46, XX) Jacob’s Syndrome/Supermale (47, XYY) 8 shorter chromosome 14 longer chromosome Burkitt’s Lymphoma (46, XY) Sex Chromosomes Most eukaryotic organisms have at least one pair of chromosomes that differ between males and females Sex Chromosomes - matching pair of homologous chromosomes in females and a partially matching pair in males ○ Males (XY) - one chromosome (Y chromosome) is much smaller than the other (X chromosome) ○ Females (XX) - two X chromosomes Sex Chromosomes Though different in size, parts of the X and Y chromosomes contain matching regions to undergo synapsis (crossing over) as a homologous pair Chromosomes that are not sex chromosomes are referred to as autosomes Sex Determination Mothers can only contribute X chromosome to offspring Fathers can contribute either an X or Y chromosome - this determines the sex of the offspring Mendelian Inheritance Inheritance Patterns Many early attempts to explain patterns of inheritance suggested that traits were determined by blending of information received by both parents We now know that information is passed from generation to generation in distinct packets called genes Gregor Mendel - The Father of Genetics We owe much of our understanding of genetics to the extensive experiments conducted by Gregor Mendel in the nineteenth century Mendel centred his attention on the common guardian pea plant for several reasons: ○ Easy to control parental crosses ○ Inexpensive ○ Annual plant (completes life cycle in one season) ○ Matured quickly ○ Produced many offspring ○ Displays several pairs of obvious, contrasting traits Mendel’s Process Mendel was able to control the crosses of different varieties of pea plants by using an artist’s brush to transfer pollen The seeds produced in this cross could then be planted to observe the next generation Mendel identiﬁed and used seven pairs of contrasting traits: ﬂour colour, ﬂower position, stem length, seed shape, seed colour, pod shape, and pod colour Mendel’s Experiments Pure-Breeding (True-Breeding) Plants - plants that produced identical offspring to the parents Cross - breeding of two organisms with different traits, resulting in a hybrid Monohybrid cross - tracking inheritance of a single trait from true-breeding parents ○ P Generation (parental generation) - crossing true-breeding plants that differed from each other in only one characteristic ○ F1 Generation (ﬁlial generation) - hybrid offspring of the P-generation cross Tall and Dwarf Pea Plants Mendel crossed purebred tall and purebred dwarf pea plants (P generation) All plants in the new generation (F1) were tall This pattern emerged again with other traits: ○ Purebred round seeded plants crossed with purebred wrinkled seeded plants resulted in only round seeded plants ○ Purebred purple ﬂowers crossed with purebred white ﬂowers resulted in only purple ﬂowers F2 Generation Mendel allowed the F1 generation of plants to self-pollinate The resulting offspring (F2 generation) had both tall and dwarf plants ○ Had both round and wrinkled seeded plants ○ Had both purple and white ﬂowers F2 Generation When recording the numbers of F2 plants based on their traits, he calculated ratios of the traits for each characteristic A pattern emerged among all characteristics: ○ In every F1 generation, one trait was present 100% of the time ○ In every F2 generation, the “missing” trait reappeared and the traits were expressed in a 3:1 ratio Mendel’s Law of Segregation Mendel concluded that traits must be passed on by discrete heredity units (factors) Though they may not always be expressed, they can still be passed on He called the factor that was expressed in all F1 generations the “dominant factor” and the factor that was hidden, then expressed in the F2 generation the “recessive factor” Mendel’s Law of Segregation Law of Segregation For each characteristic, an organism carries two factors (genes), one from each parent Parent organisms donate only one copy of each gene in their gametes. During meiosis, the two copies of each gene separate, or segregate Alleles Each form of a gene is called an allele Each parent only passes one copy of each chromosome to their offspring Anaphase of meiosis I ensures that each gamete only receives one chromosome from the pair - thus only one allele for each gene Homozygous vs Heterozygous If the two alleles for a particular gene are the same, the individual is homozygous for that allele If the two alleles for a particular gene are different, the individual is heterozygous for that allele Genotype vs Phenotype The set of alleles an individual possesses is its genotype - includes all forms of genes, even those that are “hidden” Phenotype refers to an individual’s outward appearance - the alleles that are expressed Dominant vs Recessive Dominant allele - an allele that expresses its phenotypic effect whenever it is present in the individual (can be homozygous or heterozygous for the allele) Recessive allele - only expressed when both alleles are of the recessive form (if it is homozygous for the recessive allele) Predicting Inheritance - Punnett Squares Biologists use Punnett squares to model Mendel’s analysis A Punnett square is a diagram used to predict the proportions of genotypes in the offspring resulting from a cross between two individuals Creating a Punnett Square T t 1. Deﬁne your terms a. T = tall b. t = dwarf T i. for dominant/recessive traits, use the same letter - uppercase to indicate dominance t 2. Place gametes of parents on the top and side of the square a. TT (homozygous for tall) = T & T b. tt (homozygous for dwarf) = t & t T t c. Tt (heterozygous for tall) = T & t 3. Fill in combinations of possible offspring a. Place uppercase letters ﬁrst T TT Tt 4. State the Genotypic and Phenotypic Ratio of the offspring (reduce your ratios when applicable) a. G: 1 TT: 2 Tt: 1 tt t Tt tt b. P: 3 tall : 1 dwarf Try This: P = purple Pea plants with purple ﬂowers p = white are crossed with plants with white ﬂowers. The genotype of P p the purple ﬂowers is Pp and that of the white ﬂowers is pp. Using a p Pp pp Punnett square, what will the genotypic and phenotypic ratios p Pp pp of the offspring be? G: 1 Pp: 1 pp P: 1 purple : 1 white Y = yellow Try This: y = green Two pea plants, both with Y y yellow seeds, are crossed. Some of the offspring have green Y YY Yy seeds. Using the terms phenotype and genotype, y Yy yy explain what happened. It is likely that green is a recessive allele and that both parents are heterozygous for the trait. That is, the genotypes are Yy and Yy. So, the phenotypes of the parents are yellow, but because of the genotypes, they can still produce green offspring. Probability Punnett squares provide us with the probability (measure of chance) that traits will appear ○ Probability does not equate to results - ﬂipping a coin has a 50% chance of heads or tails, however if you ﬂip a coin 10 times, it will not always land 5 times on each side ○ Each ﬂip is an independent event Punnett squares are useful tools for predicting probability and summarizing all possible combinations Test Cross Used to determine if an individual exhibiting a dominant trait is homozygous or heterozygous for that trait Performed between the unknown genotype and a homozygous recessive genotype ○ If the offspring display the dominant trait, then the individual in question is homozygous dominant ○ If the offspring displace both dominant and recessive phenotypes, then the individual is heterozygous Work well with species that reproduce quickly and in large numbers Rarely performed now with advances in genetic testing Test Cross T A tall pea plant whose t Tt tt genotype is unknown is crossed with a dwarf pea plant. t Tt tt Half the offspring are tall and half are short. What is the T t genotype of the tall pea plant? t Tt tt T = tall t = dwarf t Tt tt Dihybrid Cross Mendel’s New Experiment: Dihybrid Cross Mendel crossed two pea plants that different in two traits - pea shape and colour ○ Dihybrid Cross - a cross that involves two genes (traits) The P generation was a cross of a smooth and yellow seed (both dominant traits) with a wrinkled and green seed The F1 generation was all smooth and yellow seeds The F2 generation had a phenotypic ratio of: ○ 9 smooth yellow : 3 wrinkled yellow : 3 smooth green : 1 wrinkled green This ratio can be explained if the alleles from each trait were inherited independently of the other Walk Through A plant grown from seed which is homozygous for purple ﬂowers and tall height was crossed with a dwarf plant with white ﬂowers. Purple and tall are dominant. What are the genotypes of each plant? PPTT and pptt What are the possible gametes for each plant? PPTT → PT pptt → pt Show the gamete combinations at fertilization PT pt PpTt What are the genotypes and phenotypes of the F1 generation? Genotype: 100% PpTt Phenotype: 100% purple and tall What are the possible gametes of the F1 generation? PT, Pt, pT, and pt Use a punnett square to show the results of the cross between plants of the F1 generation PT Pt pT pt PT Pt pT pt PT Pt pT pt PT PPTT PPTt PpTT PpTt Pt PPTt PPtt PpTt Pptt pT PpTT PpTt ppTT ppTt pt PpTt Pptt ppTt pptt What are the genotypes of the F2 generation? 1 PPTT : 2 PPTt : 2 PpTT : 4 PpTt : 1 PPtt : 2 Pptt : 1 ppTT : 2 ppTt : 1 pptt What are the phenotypes of the F2 generation? 9 purple tall : 3 white tall : 3 purple short : 1 white short Mendel’s Law of Independent Assortment When two or more pairs of characteristics are considered at one time, each pair shows dominance and segregation independently of one another This law states that the inheritance of alleles for one trait do not affect the inheritance of alleles of another trait Since different pairs of alleles are passed to the offspring independently of each other there may be combinations present in the offspring not found in the parent Summary of Mendel’s Laws Mendel’s First Law - The Law of Segregation During gamete formation two alleles of a gene pair segregate from each other. A heterozygous plant (Tt) forms from gametes that are (T) and (t) in equal numbers. The gametes are not a blend of the two traits. Mendel’s Second Law - The Law of Independent Assortment Segregation of two pairs of alleles occurs independently. A plant that is heterozygous for two pairs of alleles, for example TtRr can produce four types of gametes TR, Tr, tR, tr Practice In some breeds of dogs, a dominant allele controls the characteristic of barking (B) while on a scent trail. The allele for non-barking trailing dogs is b. In these dogs an independent gene (E) produces erect ears and is dominant over drooping ears (e). For each of the following mating situations, calculate the phenotypic ratio of the offspring: 1. A non-barking trailer with heterozygous erect ears (bbEe) is mated with a heterozygous barking trailer with drooping ears (Bbee). 2. A non-barking trailer with drooping ears is mated with a heterozygous barking trailer with drooping ears. 3. A heterozygous barking trailer with heterozygous erect ears is mated with a heterozygous barking trailer with heterozygous erect ears. 4. A heterozygous barking trailer with heterozygous erect ears is mated with a non-barking trailer with drooping ears. Parents: bbEe x Bbee Gametes: bE & be x Be & be bE be Ratios: Be BbEe Bbee G: 1 BbEe : 1 Bbee : 1 bbEe : 1 bbee P: 1 Barking Erect : 1 Barking be bbEe bbee Drooping : 1 Non-barking Erect : 1 Non-barking Drooping Parents : bbee x Bbee Be be Gametes: be x Be & be Ratios: be Bbee bbee G: 1 Bbee : 1 bbee P: 1 Barking Drooping : 1 Non-barking Drooping Parents : BbEe x BbEe BE Be bE be Gametes: BE, Be, bE, be & BE, Be, bE, be BE BBEE BBEe BbEe BbEe Ratios: G: 1 BBEE : 2 BBEe : 2 BbEE : 4 BbEe : 1 BBee : Be BBEe BBee BbEe Bbee 2 Bbee : 1 bbEE : 2 bbEe : 1 bbee bE BbEE BbEe bbEE bbEe P: 9 Barking Erect : 3 Barking Drooping : 3 Non-Barking Erect : 1 Non-Barking be BbEe Bbee bbEe bbee Drooping Parents: BbEe x bbee BE Be bE be Gametes: BE, Be, bE, be & be be BbEe Bbee bbEe bbee Ratios: G: 1 BbEe : 1 Bbee : 1 bbEe : 1 bbee P: 1 Barking Erect : 1 Barking Drooping : 1 Non-Barking Erect : 1 Non-Barking Drooping Incomplete Dominance and Codominance Incomplete Dominance A situation where neither allele is dominant resulting in partial expression or blended inheritance Snapdragon ﬂowers Gene for ﬂower colour: C Allele for red: CR Allele for white: CW Homozygous CRCR plant will produce red ﬂowers Homozygous CWCW plant will produce white ﬂowers Heterozygous CRCW plant will produce pink ﬂowers Practice A pink snapdragon is crossed with another pink snapdragon. What are the phenotypic and genotypic ratios of the offspring? Practice A pink snapdragon is crossed with another pink snapdragon. What are the phenotypic and genotypic ratios of the offspring? CR = red ﬂowers CR CW CW = white ﬂowers CR CRCR CRCW G: 1 CRCR : 2 CRCW : 1 CWCW P: 1 Red : 2 Pink : 1 White CW CRCW CWCW Codominance The complete expression of two different alleles of a gene in a heterozygote Roan calves Red bull: HRHR White cow: HWHW Roan (red and white spotted) calf: HRHW Codominance and Dominance: ABO Blood Types Human blood type is both a codominant and dominant genetic trait 4 major blood types: A, B, AB, and O 3 possible alleles: IA, IB, i I = immunoglobulin - antibody found in blood plasma Each allele codes for a different enzyme that places different types of sugars (antigens) on the surface of red blood cells (IA or IB) The allele ‘i’ codes for an enzyme that makes a simpler surface molecule that lacks the extra sugars of Type A, B or AB Codominance and Dominance: ABO Blood Types Type A: IAIA or IAi (complete dominance) Type B: IBIB or IBi (complete dominance) Type AB: IAIB (codominance) Type O: ii (complete dominance - recessive trait) Immune Response Type A blood produces an immune response against type B and type AB blood Type B blood produces an immune response against type A and type AB blood Type O is the universal donor Type AB is the universal recipient Testing Blood Types If blood reacts with antibodies, the cells will stick together (coagulate) Rh factor Protein found on the surface of red blood cells If you have his protein, you are Rh positive (ex. A positive blood) If you do not have this protein, you are Rh negative (ex. O negative blood) Donating Blood Rh Factor Those with negative blood have anti-Rh antibodies in their blood - will reject positive blood Those with positive blood do not have anti-Rh antibodies - can accept the appropriate positive and negative blood ○ In pregnancy - when the blood of an Rh-positive fetus gets in the bloodstream of an Rh-negative woman, her body will recognize the Rh-positive blood is not hers. Her body will destroy the blood with anti-Rh antibodies. These antibodies can cross the placenta and attack the fetus’s blood cells. ○ Can be easily treated by suppressing the creation of anti-Rh antibodies in the mother - medication is called Rh immunoglobulin (RhIg) Practice If a woman has blood type AB and a man has blood type A heterozygous, what possible blood types could their children have? Practice If a woman has blood type AB and a man has blood type A heterozygous, what possible blood types could their children have? IA IB Their children could be A (IAIA or IAi), B (IBi) or AB (IAIB) IA IAIA IAIB i IAi IBi Pedigees Pedigree Charts A pedigree chart traces the inheritance of a certain trait among members of a family Pedigree Charts Roman numerals represent the generation and Arabic numbers represent the individuals The birth order of offspring is ordered from left to right in a family Pedigrees are examined to help trace genotypes and phenotypes in a family They are also useful for animal and plant breeders, tracking desirable and undesirable traits ○ Ex. A farmer with a prize bull can charge a high fee if a bull’s pedigree is desirable. A potential buyer may ask to see the bull’s pedigree before paying for breeding Why Incest is Not a Good Idea What percentage of the royal family has hemophilia? ○ 10/36 = 28% What percentage of the general population has hemophilia? ○ 1% When having children with people who are more closely related to you, it is more likely you will both have a recessive genetic disorder Example 1 Since the father and the daughter have Marfan syndrome, they must both have at least one dominant allele, M Everyone else does not have Marfan syndrome, so must have two recessive alleles: mm Determine which are heterozygous and which are homozygous for the trait. Since the father had two sons without the trait, he must be heterozygous. Since the mother is homozygous, the daughter must also be heterozygous. Example 2 Is it Dominant or Recessive? Is it possible to inherit a dominant trait from parents who do not express it? So, if the parents don’t express the trait, then it must be recessive. What are the Genotypes of Everyone Else? Generation I are all heterozygous for the trait. Not every other genotype can be determined. Look at II-1. That person doesn’t have children so we can’t use that to determine whether they are homozygous or heterozygous for the trait. Practice Sex Linkage Sex-Linkage Chromosomes 1 to 22 are referred to as autosomes ○ Alleles found on these chromosomes are said to be under the control of autosomal inheritance 23rd set of chromosomes are sex chromosomes ○ Alleles on these chromosomes are sex-linked Sex-Linked Disorders Most sex linked disorders are found on the X chromosome Are often recessive, though they can be dominant Sex-linked often refers to X linked disorders Examples: red-green colorblindness, hemophilia, and male-pattern baldness Assume sex-linked disorders are X-linked recessive unless otherwise stated Some disorders can be Y-linked Fewer disorders because the Y chromosome is small and does not carry as much genetic information Inheritance Patterns For an X linked (sex linked) recessive disorder: If a male inherits the X chromosome from a mother who carries the recessive allele, he will express the disorder because the Y chromosome cannot mask the effects of that allele ○ Affects males more often - if they inherit the gene, they will express it - do not have a second X chromosome to mask the gene ○ A male cannot inherit an X linked disorder from his father - receives a Y from his father Inheritance Patterns For an X linked (sex linked) recessive disorder: A female must inherit two copies of the recessive gene - one on each X chromosome - in order to express the disorder ○ Females can be carriers (not affected) if they inherit one copy of the gene Example If a mother is a carrier for hemophilia XH Xh and the father does not have hemophilia 50% chance of producing a son with hemophilia XH XHXH XHXh 50% chance of producing a daughter who is a carrier Y XHY X hY 50% chance their child will not inherit the hemophilia allele Practice A male with hemophilia mates with a woman who does not carry the hemophilia gene. Use a punnett square to answer the following: a. What is the probability of producing children who have hemophilia? b. What is the probability of producing daughters who are carriers for hemophilia? H = no hemophilia h = hemophilia XH XH XhY x XHXH Xh XHXh XHXh a. 0% chance of having children with hemophilia b. 100% chance of producing Y XHY XHY daughters who are carriers for hemophilia Practice A woman who is a carrier for color blindness has a child with a man who is colour blind. What are the genotypic and phenotypic ratios of their offspring? B = colour vision b = colour blindness XB Xb XbY x XBXb Xb XBXb X bX b G: 1 XBXb : 1 XbXb : 1 XBY : 1 XbY P: 1 colour vision : 1 colour blind Y XBY X bY Practice A woman who is a carrier for Menkes disease has children with a man who does not have Menkes disease. a. What is the probability of having a son with Menkes disease? b. What is the probability of having an unaffected offspring? M = “normal” m = Menkes disease XM Xm XMXm x XMY XM XMXM XMXm a. 50% chance of having a son with Menkes disease b. 75% chance of having an unaffected Y XMY XmY offspring A History of Evolutionary Thought Lesson 2 Eurocentric Lens Theory of evolution has been framed within a Eurocentric context Documented primarily by European male scientists Historically, ideas have been misrepresented to justify social hierarchies and inequalities Other Ways of Knowing Scientists today focus on accurately representing and using evolutionary theories Acknowledging the contributions of non-European scientists and their importance Ex. Indigenous Ways of Knowing ○ Oﬀers valuable insights into evolution ○ Engage in selective breeding, respect for biodiversity, track changes in the environment Indigenous Ways of Knowing Wolves on B.C’s mainland feed on deer, moose, and beaver Wolves on the islands of of the B.C coast eat salmon and are excellent at catching ﬁsh and digging for clams Indigenous Ways of Knowing When scientists were going to study the wolves, they recruited an Indigenous elder from the Heiltsuk First Nations community who asked, “What wolves are we going to study? The timber wolves or the coastal wolves?” Indigenous Ways of Knowing At the time, the scientists believed that only one kind of wolf crossed freely between the islands and the mainland Chester Starr shared that his father watched the wolves get salmon from the river Over time, the wolves origin territory was logged, noting each group had unique diets and behaviours based on their location Indigenous Ways of Knowing Genetics tests show that the two groups of wolves are far diﬀerent than what was previously expected for such close neighbours Science and Indigenous knowledge, even using diﬀerent approaches, can reach the same conclusions and beneﬁt from each other Religious Beliefs A number of religions believe in the account in the Bible of how the world was created. Belief that God created each species in their present form. Faith & Science Don’t give up your beliefs, but be open to seeing how the scientiﬁc method supports natural selection. Faith & Science The Theory of Evolution also has many ﬂaws in it and parts that can’t be backed by data. A History of Evolutionary Thought By the eighteenth century, scientists were beginning to gather evidence supporting the theory that life had changed over time. Georges-Louis Leclerc, Comte de Buffon (1707-1788) A French scientist, Georges-Louis Leclerc, studied animal body structures to ﬁnd their function. Georges-Louis Leclerc, Comte de Buffon (1707-1788) Buﬀon was puzzled by vestigial organs – features or structures that have no apparent function. Ex. Why do pigs and other mammals have toes that don’t reach the ground. Georges-Louis Leclerc, Comte de Buffon (1707-1788) Buﬀon believed the species had been created in a more perfect form but had changed over time. A History of Evolutionary Thought Even with observation, these scientists could not oﬀer a scientiﬁc explanation for how living things change. Jean-Baptiste Lamarck (1744–1829) Lamarck proposed that evolutionary change resulted from two distinct principles. Lamarck’s First Principle: Use and Disuse First principle: The use or disuse of a structure would lead to its development or diminishment. Lamarck’s First Principle: Use and Disuse Lamarck believed that structures an individual used became stronger, while structures that were not used became weaker. Lamarck’s First Principle: Use and Disuse First principle: The use or disuse of a structure would lead to its development or diminishment. ★ How might Lamarck’s theory be ﬂawed? Lamarck’s First Principle: Use and Disuse Flaw: Many features do not change in response to use, or become weaker in response to use. Example: Your vision does not improve the more you use your eyes. Lamarck’s Second Principle: Inheritance of Acquired Characteriﬆics Second principle: Individuals can pass on to their oﬀspring characteristics that they had acquired during their lives. Lamarck’s Second Principle: Inheritance of Acquired Characteriﬆics Lamarck believe that if an adult giraﬀe stretched its neck during its lifetime, then its oﬀspring would be born with slightly longer necks. Lamarck’s Second Principle: Inheritance of Acquired Characteriﬆics Second principle: Individuals could pass on to their oﬀspring (heritable) characteristics they had acquired during their lives. ★ How might Lamarck’s theory be ﬂawed? Lamarck’s Second Principle: Inheritance of Acquired Characteriﬆics Flaw: Acquired characteristics during life are not normally heritable. Example: Losing a limb will not cause your child to be born without a limb. Question Based on Lamarck’s theory of evolution, what could you do to ensure your children were born with enhanced musical abilities? Lamarck’s Contributions Lamarck’s contributions to evolutionary thought: 1. All species evolve over time. 2. A species evolves in response to its environment and becomes better adapted to that environment. 3. Changes are passed on from generation to generation. What do we know about fossils? Georges Cuvier (1769–1832) Cuvier noticed that fossils from deeper layers were simpler than the more complex fossils above. ★ Why might that be? Georges Cuvier (1769–1832) Catastrophism: Species did not change but were eliminated by catastrophic events, only to be replaced by newly created sets of species. Charles Lyell (1797–1875) Uniformitarianism: Earth’s geologic features can be explained by very slow changes occurring over very long periods of time. Charles Lyell (1797–1875) Lyell suggested that the Earth was extremely old and life underwent evolutionary change over time. A History of Evolutionary Thought Although there was growing evidence that Earth was ancient, and species were evolving, the mechanism for evolution was still unknown. Video 1. Buﬀon, Lamarck, Cuvier 7:30-12:00 Charles Darwin (1809-1882) The English scientist Charles Darwin was the founder of the modern theory of evolution. Charles Darwin He collected fossils and observed variations among living things on the Galapagos islands. Where are the Galapagos Islands? Galapagos Islands: A Naturalist’s Dream Unique and vast biodiversity can be found here. Remote islands presented with unique conditions for biodiversity. Home to the longest living vertebrate on earth: the Giant Tortoise Charles Darwin In 1859, Darwin (hesitantly) published his theory of evolution in a book called On the Origin of Species. ★ Darwin’s Theory of Evolution 1. Species change over time. 2. All species are descended from a common ancestor. 3. Natural selection is the central mechanism driving evolution. 4. Species gradually adapt to their environment through the accumulation of beneﬁcial traits. Textbook Readings & Questions 7.2 Readings - pg. 288 - 293 7.2 Questions - Q1 - 4, 8-10 7.3 Readings - pg. 294 - 295 The Origin of Species: The Making of a Theory Natural Selection Biological Change over Time Variations in genes cause differences in an individual’s traits—how it looks, or its behavior Genetic variations occur mostly by chance as genes copy themselves to make new cells Mistakes, called mutations, sometimes occur during the copying process Mutations Mutations may be neutral, harmful, or beneﬁcial A neutral mutation does not help or harm the organism's ability to survive or reproduce Example: Heterochromia, the presence of different coloured eyes Mutations A beneﬁcial mutation increases the survival and reproductive success of an organism Example: Sickle-cell allele gives the carrier a high degree of resistance to malaria, dramatically enhancing their chances of survival in regions where malaria is present A mutation that gives an animal better vision or faster legs would be a beneﬁcial mutation. These traits help it ﬁnd food and avoid enemies Beneﬁcial mutations give the individual an advantage over others of its kind. It will be more likely to reproduce and pass its genes along to the next generation Mutations A harmful mutation decreases the survival and reproductive success of an organism Example: Albinism in organisms is a harmful mutation that fails to produce melanin, a pigment that protects against the radiation of the sun Harmful mutations may cause genetic disorders or cancer Artiﬁcial Selection Artiﬁcial selection is where humans select plants or animals with desirable traits in one generation as the breeding stock for the next generation Artiﬁcial Selection Farmers select speciﬁc seeds from plants that exhibited desirable traits to sow the next season Examples of Artiﬁcial Selection: Bananas were artiﬁcially selected over hundreds of years for desirable traits such as sweet, thin, easy to peel, and seedless Thousands of years of artiﬁcial selection have produced a great variety of dog breeds Origin of Species (1859) Darwin outlines 2 key ideas: Descent with Modiﬁcation (Evolution) The idea that species change over time, give rise to new species, and share a common ancestor Evolution occurs when there is a change in the heritable information passes from one generation to the next Natural Selection A process in which some organisms have a better ability to survive in their environment, increasing their reproductive success and passing on their genes Through natural selection, species become adapted, or better ﬁt, to their environments Try This: Natural Selection in Tadpoles A few years ago a biologist looked into a small pond with a gray, muddy bottom and counted about 500 tadpoles. Most were dark, but 75 were white (albinos). The next morning tracks of a raccoon were seen at the edge of the pool. The biologist counted only 49 white tadpoles that day; the next morning only 27; and the third morning only 9. On the fourth morning he found only 7 albino tadpoles. On that day he carefully estimates the number of dark tadpoles to be about 400. On each of the four mornings there had been fresh raccoon tracks. Try This: Natural Selection in Tadpoles 1. If the raccoon was wholly responsible for the disappearance of tadpoles, how many of the dark ones had it eaten? How many white ones had it eaten? Dark: ____________ ; White: _____________________ 2. Why do you suppose the raccoon caught more white tadpoles than dark ones? 3. What prediction would you make for the pond’s tadpole population the following year? 4. If this pond had a white, sandy bottom, which colour tadpole would the raccoon probably catch more frequently? 5. The text says there were dark and white tadpoles, this is likely a simpliﬁcation, explain. VISTA Consider the acronym VISTA to understand the mechanism of Natural Selection Variation - in all species, individual differ in their genetic makeup, producing many variations of physical features; individuals in a population vary from each other Inheritance - individuals pass some of their genetic material to their offspring, traits are inherited from parents VISTA Selection - environments cannot support unlimited populations, some traits provide individuals with a better chance of surviving and producing offspring Time - over time, selection results in changes in species, these traits are passed on to greater number of offspring, successful variations accumulate over time Adaptation - the result is a population that is better suited (adapted) to the environment Fitness Fitness describes the relative ability to survive and reproduce Certain adaptations make individuals of species better suited to the environment An organism that has many viable offspring has high ﬁtness; an organism that has few viable offspring has low ﬁtness Selecting for a “Perfectly-Engineered” Trait There are many reasons why natural selection may not produce a “perfectly-engineered” trait ○ For example, cheetahs would be more ﬁt if they could run a little fast and catch more prey Selecting for a “Perfectly-Engineered” Trait Lack of necessary genetic variation - if the genes are not present, evolution will not happen If the genes to be faster are not available in the cheetah population, through mutation or gene ﬂow, then the population will not evolve to be faster Selecting for a “Perfectly-Engineered” Trait Trade-offs - gaining one feature may come at a harmful cost - there may be no net increase in ﬁtness as a result of faster genes Running faster may come at too high of a metabolic cost Developing longer limbs may result in faster strides, but may result in them becoming more fragile Human Skin Color: Evidence for Selection Activity Educator Materials OVERVIEW This activity supports the viewing of the short film The Biology of Skin Color. Students watch the film in segments and use real data to propose hypotheses, make predictions, and justify claims with evidence. KEY CONCEPTS Within a population, heritable traits that provide a survival and reproductive advantage in a particular environment are more likely than other traits to be passed on to the next generation and thus tend to become more common over time. These traits are known as adaptations. Human populations living in different parts of the world have different sets of evolutionary adaptations. These include wide-ranging variations in the way people look, especially with respect to skin color. Evidence from different disciplines can inform what makes a human trait beneficial or harmful in a particular environment. Evolution involves tradeoffs; a change in a gene that results in an adaptation to one aspect of the environment may be linked to a disadvantage with respect to another aspect of that same environment. STUDENT LEARNING TARGETS Make predictions and propose hypotheses based on available information; and Use real data presented in scientific figures and information from the film to make evidence-based claims. PRIOR KNOWLEDGE Students should have a basic understanding of evolution and natural selection. TEACHING TIPS You may want to watch each clip of the short film as a class and address any questions students might have after each viewing. Students can then work independently or in small groups to examine the figures and answer the associated questions. Alternatively, you may want to project the figures and examine them together as a class and then let students answer the questions independently. ANSWER KEY PART 1: Is There a Connection Between UV Radiation and Skin Color? 1. Describe the relationship between the UV Index (the colored bar in Figure 1) and latitude (y-axis). UV radiation is most intense near the equator and least intense toward the poles. Students may also say it is most intense at lower latitudes and increasingly intense as latitude increases. 2. How do you explain the relationship between the UV Index and latitude? (In other words, why does UV intensity change with latitude?) The answer has to do with the angle of Earth relative to the sun. Latitudes at the equator receive direct sunlight year-round. Latitudes toward the poles receive sunlight at an oblique angle, which means that the same amount of radiation is spread out over a larger area than at the equator. 3. Find your approximate location on the map. What is the primary UV Index value of your state on this particular day in September? Answers will vary depending on location. Most states in the U.S. have a UV index between 4 and 6. Human Evolution Revised April 2018 www.BioInteractive.org Page 1 of 4 Activity Human Skin Color: Evidence for Selection Educator Materials 4. Look at the regions that receive the most-intense UV (light pink). Site a specific piece of evidence from the map that a factor other than latitude was contributing to UV intensity on this day. The Andes and Himalayas have higher UV Index values than you’d expect, which is evidence that UV intensity increases with higher altitude. Students may also say that there might be decreased cloud cover or greater humidity. All these answers would be acceptable. 5. In the film, Dr. Jablonski explains that melanin, located in the top layer of human skin, absorbs UV radiation, protecting cells from the damaging effects of UV. Genetics determines the type of melanin (i.e., brown/black eumelanin or red/brown pheomelanin) and the amount of melanin present in an individual’s cells. Based on this information, write a hypothesis for where in the world you would expect to find human populations with darker or lighter skin pigmentation (i.e., different amounts of melanin). Answers will vary, but students may predict that populations with darker skin color (or more eumelanin) would be found in regions with more intense UV radiation. Thus, populations found in equatorial areas will have the darkest skin (most eumelanin) and populations at higher latitudes will have lighter skin (least eumelanin). 6. Explain how scientists could test this hypothesis. Scientists could measure the average skin color of people at different locations throughout the world and compare that to average annual UV intensity. 7. Why do you think that reflectance data are collected from a subject’s inner arm? The inner arm is not usually affected by environmental factors (e.g., it doesn’t tan). 8. Describe the relationship between skin reflectance (y-axis) and latitude (x-axis). Consider both the direction and steepness of the lines’ slopes. Skin reflectance increases as you move north and south from the equator. That means that skin is darker near the equator and lighter as you move north or south. 9. Do these data support your hypothesis from Question 5? Justify your answer. This graph indicates that darker-skinned individuals (individuals with more eumelanin in their skin that reflects less visible light) tend to live around the equator, where UV intensity is highest. Student responses may vary about whether the findings support their hypothesis from question 5. 10. Based on what you know about skin pigmentation so far, suggest a mechanism by which UV intensity could provide a selective pressure on the evolution of human skin color. In other words, propose a hypothesis that links skin color to evolutionary fitness. Students may propose that melanin protects an individual from skin cancer. While this is true, it may not account for the selection for dark skin, as they will learn in the upcoming film segment. Melanin also protects circulating folate from being broken down by UV radiation. PART 2: What Was the Selective Pressure? 11. What does it mean for a trait, such as light skin coloration, to be under negative selection in equatorial Africa? Relate negative selective pressure to what we know about MC1R allele diversity among African populations. It means that there is selection against that trait. Researchers found that among people of African ethnicity, there is very little variation in MC1R alleles; almost everyone has the allele associated with the darker skin trait. There is selection against any MC1R alleles that do not code for darker skin. 12. Why does Dr. Jablonski dismiss the hypothesis that protection from skin cancer provided selection for the evolution of darker skin in our human ancestors? Because skin cancer does not usually arise until after an individual’s peak reproductive years. To be Human Evolution Revised April 2018 www.BioInteractive.org Page 2 of 4 Activity Human Skin Color: Evidence for Selection Educator Materials affected by natural selection, a trait must have an effect on an individual’s ability to survive and pass on its genes. 13. Revisit your hypothesis from Question 10. Based on the information you have now, does this seem like a more or less probable hypothesis than when you first proposed it? Provide evidence to support your reasoning. Answers will vary. If the student had hypothesized that protection from skin cancer provided the selective pressure, based on this information they might want to revisit their hypothesis. 14. Describe the relationship between folate levels and UV exposure. Use specific data from the graph to support your answer. The group exposed to UV radiation has less serum folate. The mean concentration for the “normal” group was about 7 ng/mL and the mean concentration for the “patient” group was about 4 ng/mL. 15. Dr. Jablonski describes learning that low folate levels are linked to severe birth defects as a “eureka moment.” Explain what she means by this. Dr. Jablonski saw a connection between phenotype (skin color), environment (UV intensity), and fitness (folate levels and the risk of severe birth defects and low sperm counts). This connection provides an alternative hypothesis for the selective pressure that drove the evolution of darker skin. 16. Based on this new information, revise your hypothesis to explain the selective pressure on the evolution of human skin color. The greater amount of eumelanin in darker skin protects folate from being broken down by UV radiation and thus increases fitness among populations in high-intensity UV areas. 17. Can the effects of UV light on folate explain the full variation of human skin color that exists among human populations today? Explain your reasoning. Protection of folate from destruction can explain the selective pressure for the evolution of darker skin. However, it does not explain why there is variation in human skin color. What is the selection for the evolution of lighter skin? PART 3: Why Aren’t We All Dark Skinned? 18. Based on these data, describe the populations least likely to synthesize sufficient levels of vitamin D. Explain your answer with data from the figure. Dark-skinned people are least likely to have sufficient vitamin D. They cannot produce enough vitamin D regardless of where they live. Moderately dark-skinned people can synthesize enough vitamin D if they live near the equator. 19. How do these data support the hypothesis that the evolution of lighter skin colors was driven by selection for vitamin D production? Light-skinned individuals are better able to synthesize sufficient vitamin D, especially at higher latitudes. That means that light skin increases fitness away from the equator. 20. For a person living farther away from the equator, would the risk of vitamin D deficiency be uniform or vary throughout the year? If it would vary, how would it vary? Explain your reasoning. UV intensity varies with the seasons. A person would be at a higher risk for vitamin D deficiency in the winter, when UV radiation is less intense. 21. Vitamin D and folate levels in the blood are both affected by UV light. Describe the predicted effects of using a tanning booth (which exposes skin to UV light) on the blood levels of these two vitamins. Being in a tanning booth would increase the amount of circulating vitamin D and decrease the levels of folate. It can also put the individual at greater risk of developing skin cancer. Human Evolution Revised April 2018 www.BioInteractive.org Page 3 of 4 Activity Human Skin Color: Evidence for Selection Educator Materials 22. Based on everything that you have learned so far, provide an explanation for how the different shades of skin color from pinkish white to dark brown evolved throughout human history. Darker skin colors evolved because they provided increased fitness in early human populations living in equatorial Africa. Darker skin protects circulating folate from being broken down. Some human populations migrated out of Africa to places where UV radiation was less intense. Here there was selection for lighter skin which let more UV radiation through for vitamin D synthesis. Thus the evolution of variation in human skin color is due to the balance between needing protection from UV to maintain circulating folate levels and needing some UV to prevent vitamin D deficiency. PART 4: How Does Recent Migration Affect Our Health? 23. Describe the trends visible in the data. Which subpopulation (gender, race/ethnicity) is at the greatest risk for vitamin D deficiency? Which subpopulation is at the least risk for vitamin D deficiency? Non-Hispanic blacks have the lowest mean vitamin D levels overall and among males and females living in the United States. Non-Hispanic whites have highest mean vitamin D levels overall and among males and females. The subpopulation at the greatest risk for vitamin D deficiency is non-Hispanic black females. The subpopulation at the least risk for vitamin D deficiency is non-Hispanic white males. 24. What is one of the consequences of recent human migrations on human health? One consequence is that people’s skin color may not be a good match for the UV radiation intensity where they live. REFERENCE This lesson was adapted from the case study “The Evolution of Human Skin Color” by Dr. Annie Prud’homme- Généreux published by the National Center for Case Study Teaching in Science. http://sciencecases.lib.buffalo.edu/cs/collection/detail.asp?case_id=584&id=584 CREDITS Reviewed by Annie Prud’homme-Généreux, PhD, Quest University, Canada. Edited by Laura Bonetta, PhD, HHMI, Melissa Csikari, HHMI, and Stephanie Keep, consultant. Human Evolution Revised April 2018 www.BioInteractive.org Page 4 of 4 Evidence for Evolution Lesson 5 Reminders Origami Bird Natural Selection Lab due yesterday Evolution quiz - tomorrow Wednesday Nov 20th ○ Extra-help/quiz review - today at lunch OSSLT schedule this week Darwin’s Evidence for Evolution Darwin collected many forms of evidence that convinced him of the evolution of species and enabled him to formulate his theory of evolution. 1. Fossil Records Evidence for evolution comes from fossils of living things preserved in the ground. Fossil Record Darwin noticed some fossils of extinct animals were similar to living species today. Fossil Evidence of Evolution Fossils show how certain organisms changed over time. Evolution of Horses For example, the bones of horses from more than 50 million years ago show that early horses were about the size of modern dogs. Ancestor of Horses This horse lived in woodland, eating leaves, nuts and fruit with its simple teeth. Horses had Toes instead of Hooves! Instead of hooves, a horse had 4 functional toes on the front feet and 3 functional toes on the hind feet. Ancestor of Horses Environmental changes (ex. forests shrank, grassland expanded) led to horses changing over time. Ancestor of Horses Populations of horses now ate grass, grew larger, and ran faster because they had to escape faster predators. Ancestor of Horses Ex. because grass wears teeth out, horses with longer-lasting teeth had an advantage. Evolution of Horses Bones from several later stages of the horse show that they got bigger over time. Evolution of Horses Modern Horses Today, horses have teeth that never stop growing, single-toed hooves, great long legs for running. 2. Biogeography Evidence for evolution also comes from biogeography – the geographic distribution of species. The Galapagos Islands Darwin was surprised by the unusual assortment of species he found on the Galapagos Islands. Imagine Yourself as Darwin... You make a lot of observations of the unique species on the remote Galapagos Islands. How could you explain the species that you see? Galapagos Islands Observation: Many species of plants, birds, insects, and reptiles, but very few land mammals. How could you explain this? Remote Islands Explanation: Only organisms that are able to cross open ocean by water or air reach remote islands. ★ How do plants reach remote islands? Galapagos Islands Observation: Many unique species found nowhere else on Earth. How could you explain this? Remote Islands Explanation: Over time, ancestral species evolved into new geographically isolated species. Galapagos Islands Observation: Unique species most closely resemble species on the nearest continental land mass. Remote Islands Explanation: Unique species are descendants of ancestral species from the nearest continental land masses and will exhibit some similarities. Biogeography Evidence that remote islands are populated by species that evolved from species that had travelled from the closest major land mass. 3. Homologous Features Further evidence for evolution: homologous features. Homologous Features Many modern species share physical features that serve diﬀerent functions. Homologous Features Darwin considered why similar structures of two organisms could or would have entirely diﬀerent functions. Homologous Features Darwin wondered: Why would a ﬁnger bone be useful in a whale? Why would the skull of a whale have the same number of bones as the skull of a mouse? Why were the bones of all mammals so similar in number and arrangement? Homologous Features Ex. skeletal arrangement of a bat vs human Minds On! Guess what organism the forelimb belongs to! Homologous Features They all possess very similar bone structure. How could you explain this? Human Arm Horse Leg Cat Leg Bat Wing Whale Flipper Homologous Features They may all have inherited this feature from a common ancestor! Homologous Features Physical features shared due to a common evolutionary origin (inherited from a common ancestor) are homologous. May serve diﬀerent functions in modern species. 4. Similarities in Embryonic Development Similarities in embryonic development between species provides evidence of evolution from a common ancestor. Similarities in Embryonic Development Closely related species share similar developmental processes and patterns. Similarities in Embryonic Development Ex. in early developmental stages, the embryos of all vertebrates, including humans, chickens, and ﬁsh, possess a short bony tail. Similarities in Embryonic Development Guess which animal embryo! Similarities in Embryonic Development 5. Analogous Features Evolutionary relationships can also account for diﬀerences in the structure of analogous features Analogous Features Structures in diﬀerent species that serve similar functions but do not share the same evolutionary origin. Analogous Features Wings on birds and insects serve the same function but are diﬀerent in structure. Insects and birds are distantly related and features have evolved independently of each other. 6. Vestigial Features Another evidence for evolution is vestigial features. Vestigial Features Features that lack an apparent purpose in modern animals and no longer serve the function they do in similar species and ancestral species. Minds On! Guess what organism each foot belongs to! Vestigial Features How could you explain this in terms of evolution? Vestigial Features Vestigial features may have served a useful purpose in an ancestor, but became useless or greatly distorted as the species evolved. Vestigial Features Many large snakes and whales have hip bones which are homologous to hip bones that support the hind limbs of other vertebrates. Minds On! What are some vestigial features in humans? Vestigial Feature in Humans: Goosebumps Goosebumps were once used to make animals appear larger to scare off predators and help keep mammals warm. 7. Competition within Populations Darwin noticed that many species produce large numbers of oﬀspring, but not all survived, resulting in competition within species. Darwin wondered if nature favoured certain individual’s traits over others in a struggle for survival. Darwin’s Evidence Darwin not only collected evidence leading him to believe that species had evolved, but his theories could explain HOW they evolved. Evidence for Evolution from DNA Darwin could compare only the anatomy of living things. Today, scientists can compare their DNA! 8. DNA Similarity Similar DNA sequences between species are the strongest evidence for evolution from a common ancestor. DNA Similarity Scientists compare the DNA of diﬀerent species and identify similarities. DNA Similarity DNA can reveal how related diﬀerent species are, and when genetic mutations occurred. Video Textbook Readings & Questions 7.4 Readings - pg. 296 - 302 7.4 Questions - Q1 Mechanisms of Evolution What is Evolution? Evolution is a change in the genetic material of a population over time. Evolution Evolution takes place through mechanisms that drive a change in the allele frequencies in a population. Natural Selection Evolution without Selection Natural selection is an important mechanism of evolution. But is it the only mechanism? Nope! Sometimes evolution just happens by chance. Random Chance When individuals produce offspring, the likelihood of passing on any particular allele is subject to random chance. Hence, the genetic makeup of a population can change simply by chance. Genetic Drift Unlike natural selection, genetic drift does not depend on an allele’s beneﬁcial or harmful effects. Genetic Drift Genetic drift changes allele frequencies purely by chance, as random subsets of individuals are sampled to produce the next generation. Genetic Drift Genetic drift is changes to allele frequency as a result of chance. Genetic Drift Genetic drift is the random shifting of the genetic makeup of the next generation. Genetic Drift The smaller the number of individuals in a population, the greater the inﬂuence of genetic drift. Genetic Drift In small populations, genetic drift can result in a particular allele becoming either very common or disappearing entirely over generations. Genetic Drift In larger populations, genetic drift does not change allele frequencies signiﬁcantly. Bottleneck Effect The bottleneck effect is an extreme example of genetic drift that happens when the size of a population is severely reduced. Bottleneck Effect Events like natural disasters (earthquakes, ﬂoods, ﬁres) can decimate a population, leaving behind a small, random assortment of survivors. Bottleneck Event A bottleneck event is a drastic reduction in population size that results in a loss in genetic diversity. Bottleneck Event How can a bottleneck event reduce genetic diversity? Imagine a bottle ﬁlled with marbles, where the marbles represent the individuals in a popula

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