Chapter 12: Mechanisms of Evolution (SCB 101) - PDF

Chapter 12: Mechanisms of Evolution SCB 101 Prof. Calkins Recap: Define evolution: Biological theory that states that all organisms are related and change over time Recap: What are the six pieces of evidence for evolution? 1. Direct observation through artificial selection 2. F...

Chapter 12: Mechanisms of Evolution SCB 101 Prof. Calkins Recap: Define evolution: Biological theory that states that all organisms are related and change over time Recap: What are the six pieces of evidence for evolution? 1. Direct observation through artificial selection 2. Fossil evidence 3. Shared characteristics among living organisms 4. Similarities and differences in DNA 5. Biogeographic evidence 6. Common patterns of embryo development Mechanisms of Evolution Natural Mutatio Gene selectio n flow n Sexual Genetic selectio drift n  Process by which individuals with advantageous inherited characteristics for a particular environment survive and reproduce at a higher rate than do individuals with other, less useful Natural characteristics Selection Individuals with traits that HELP them survive will live longer, and pass on those traits to their offspring helping them survive longer, too. Charles Darwin British Naturalist known for his contributions to the theory of evolution Traveled the globe observing species and occurrences in nature His observations of fossils, and wildlife led him to his discoveries Darwin’s Journey Darwin served as a naturalist aboard the H.M.S. Beagle. They traveled from Spain to South America, along the coast of Australia, and the horn of Africa He studied the plants and animals of S. America, and was particularly interested in the animals of the Galapagos Islands Galapagos Islands The Galapagos Islands are located about 600 miles west of Ecuador Darwin observed many endemic species that were local to the Galapagos and found nowhere else  Darwin’s Finches Slightly different beak shapes based on habitat and diet.  “Descent with Modification” The mechanism whereby individuals with certain heritable traits have an Darwin’s increased chance of surviving and producing offspring Theory It is based on three observable facts of nature… Descent with Modification Variations that confer survival advantage are passed onto the next generation Over time, species become better adapted to their environment Populations may become so different they split into separate species  Darwin observed: 1. Individuals in a population vary from one another 2. Variations are inherited Darwin’s 3. In every population, many offspring die before reaching maturity Observati ons Which offspring survive? Why? Individuals that are better at surviving will pass these variations onto their offspring Recap: Darwin’s finches supported the idea of evolution because a. Even though they changed over time, they were all still the same finch species. b. Every continent has its own species of finch. c. They were clearly all finches but they had adapted and changed to suit different environments on different islands. d. The finches supported the idea of natural selection, but not evolution. Recap: Darwin Observed that Natural selection requires three facts of nature. These are: a. Species endemic to islands, individual variation, and not all offspring survive b. Individual variation, variations are inherited, and not all offspring survive c. Individual variation, parental variation, and not all offspring survive d. Individual variation, variations are inherited, offspring reproduce  Define the following terms: Alleles: different version of the same gene Gene: Review: sequence of DNA Phenotype: what is visible in the population Genotype: the complete gene library of the organism The Modern Synthesis Darwin could not explain why or how traits were passed along Merging genetics and evolutionary biology led to an understanding that natural selection explained how the number of alleles present in a population (allele frequency) could change over time Evolutionary change occurs when allele frequencies in a population change over time. The Modern Synthesis Mathematical models predict how populations evolve. Predictions can be tested in the lab and in the field. Provides overwhelming support for evolutionary theory Allele Frequencie s Allele frequencies: percentages of a specific allele in a population Mice with: Two white-fur- pigment alleles appear white Two black-fur- pigment alleles appear gray One black and one white allele appear gray Recap The Modern Synthesis refers to our current understanding of how evolution by natural selection works. Darwin couldn’t explain it at the time he was working on the idea. What was he missing? a. He didn’t see that individuals varied. b. He didn’t have access to enough species to test his ideas. c. He didn’t understand how the allele frequency of a population provides the necessary variation. d. He did not understand Mendel’s work with Pea Plants  Natural selection: the process by which a population’s allele frequency changes over time enabling it to survive better than Natural other populations Selection Favorable traits become and the increasingly common in future generations because unfavorable Modern traits are lost when organisms die Synthesis or fail to reproduce. As we know, traits are passed along in the form of genes/alleles Case Study: Natural Selection Peter and Rosemary Grant : 40 years of research on the Galapagos finches Medium ground finches are seed eaters with variable beak size Birds with larger beaks eat large, tough seeds Birds with smaller beaks eat smaller seeds Case Study: Natural Selection 1976 – 1977: severe drought reduced the number of seeds available 80% of the finches died Only large, hard seeds were available Drought conditions gave birds with large beaks a survival advantage Case Study: Natural Selection Average beak depth increased 7% in a few seasons. Evidence for Natural Selection Larger-beaked birds survived drought and passed alleles onto offspring Adaptation is a property of populations, not individuals Selection is not necessarily unidirectional: in wet years, smaller beaked birds fare better From Bozzone, Biology for the Informed Citizen, © 2014 by Oxford University Press  A change in the sequence of any segment of DNA New alleles are generated when mutations occur in germ cells (sex cells) of sexually reproducing Mutations organisms So…. Mutations that make alleles that confer a survival advantage tend to stick around in populations through natural selection. Mutations and Evolution In asexually reproducing organisms such as bacteria, mutations can happen rapidly, causing extremely quick evolution of species Bacteria that survive antibiotic attacks reproduce and become more common. Natural selection promotes adaptive traits, and the population becomes better suited to its environment. Natural selection is what allowed staph to adapt to our use of antibiotics. Evolution Game The Evolution Game Evolution Game Report What traits did you change in following generations? How did these changes affect your population? What happens when you increase the chances of mutation for Speed Size Sense How does this relate to how evolution by natural selection works?  Gene flow: the exchange of alleles among populations Gene Flow Members of some populations move to other’s and bring their genes with them  Genetic drift: a change in allele Genetic frequencies in a population due to random differences in survival rates Drift Genetic Drift- Bottleneck Genetic Bottleneck: a drop in the size of a population, for at least one generation, that causes a loss of genetic variation Caused by random events Earthquakes, volcanic activity, hurricanes…. Etc. Genetic Drift- Founder’s Effect Special case of genetic drift A few individuals leave and begin a new population The new population is genetically different In a new habitat, the new population may adapt in different ways  Sexual selection: when nature Sexual selects a trait that increases an individual’s chance of mating Selection Even if that trait decreases an individual’s chance of survival Sexual Dimorphism The more elaborate the peacock plumage: The more mates he attracts The more difficult it is to evade predators The more mating calls a male túngara frog makes: The more mates he attracts The more bats he attracts that try to eat him Recap: A genetic bottleneck is a type of genetic drift in which a. a trait increases an individual’s chance of mating. b. distantly related organisms evolve similar structures. c. a few individuals from a large population establish a new population with limited alleles. d. a population is reduced to very few individuals and alleles are lost. Recap: Which of the following is the only one that can generate new alleles? a. genetic drift b. sexual selection c. mutation d. the founder effect Recap: In order to contribute to the evolution of one’s species, an individual must survive in its environment long enough to a. leave its birth group (such as a family). b. reach sexual maturity. c. reproduce. d. adapt to changes in its environment.