Ecb6 Lecture Ch19 PDF - Sexual Reproduction and Genetics

CHAPTER 9 CHAPTER 19 Sexual Reproduction and Genetics Dr. Moe Abbas Copyright © 2023 by W. W. Norton & Company, Inc.  For Chapter 9, you are only responsible for what is in this lecture For chapter 19 you are responsible for this lecture and the book  For your...

CHAPTER 9 CHAPTER 19 Sexual Reproduction and Genetics Dr. Moe Abbas Copyright © 2023 by W. W. Norton & Company, Inc.  For Chapter 9, you are only responsible for what is in this lecture For chapter 19 you are responsible for this lecture and the book  For your last lecture: Generating genetic variation THE BENEFITS OF SEX MEIOSIS AND FERTILIZATION MENDEL AND THE LAWS OF INHERITANCE GENETICS AS AN EXPERIMENTAL TOOL EXPLORING HUMAN GENETICS Generating genetic variation Horizontal gene transfer (more predominant in prokaryotes) Don’t confuse it with Vertical gene transfer in eukaryotes non-sexual movement of genetic information between genomes. Incoming DNA or RNA can replace existing genes, or can introduce  Point Mutations and their effect Point Mutations Are Caused by Failures of the Normal Mechanisms for Copying and Repairing DNA Mutations Can Also Change the Regulation of a Gene DNA Duplications Give Rise to Families of Related Genes  The globin case of gene duplications Fetal hemoglobin has a higher affinity for oxygen > adults. A property important for oxygen transfer from mother to child. 2nd duplication Most gene event duplications are 1st duplication not functional and event are heavy with mutations. We call them pseudogenes. Question: Why do cells keep non functional genes? Why  The bulk of the human genome is made of repetitive nucleotide sequences and other non-protein-coding DNA. LINEs (long interspersed nuclear elements) = 6000 – 8000 bps SINEs (short interspersed nuclear elements) = 500 Class of DNA sequences known as transposable elements (TEs). TEs can bps move and duplicate themselves within the genome, which can result in the creation of new, repetitive DNA sequences. They do not code for proteins; instead, they play various roles in chromosome structure and function.  The bulk of the human genome is made of repetitive nucleotide sequences and other non-protein-coding DNA. Some scientists classify LINEs and SINEs as retrotransposons DNA transposons move using a cut-and-paste mechanism. In contrast, retrotransposons move in a copy-and-paste fashion by duplicating the element into a new genomic location via an RNA intermediate. Thus, retrotransposons increase their copy number more rapidly than DNA transposons.  The bulk of the human genome is made of repetitive nucleotide sequences and other non-protein-coding DNA. Simple sequence repeats (SSRs) or microsatellites are DNA stretches consisting of short, tandemly repeated di-, tri-, tetra-or penta-nucleotide motifs  The bulk of the human genome is made of repetitive nucleotide sequences and other non-protein-coding DNA.  The bulk of the human genome is made of repetitive nucleotide sequences and other non-protein-coding DNA. Chapter 19!  THE BENEFITS OF SEX What is the ultimate goal of Cells? Reproduction is a way to make new organisms that can grow. Thus, every organism’s apparent “goal” is to fill the available world with its offspring, that is, with "self". Asexual Sexual reproduction reproduction Fast, allows a In general, slow leads theocratically to genetically different unlimited number of organisms. identical offspring’s. Most multicellular Identical to the organisms are here parental line but not all (Observation not a rule!) Parthenogenesis: oocytes that develop with out sperm/fertilization Extra reading if you like: Sexual reproduction in Paramecium and  Sexual reproduction involves both Diploid and haploid cells 2 n 2n 1 copy copies Most Cells are Diploids or haploids Extra reading if you chromosomes Polytene like of plants and fruit flies can be 1024-ploid.Ploidy of systems such as the salivary gland, elaiosome, endosperm, and trophoblast can exceed this, up to Homologous 1048576-ploid in the silk glands of the Chrs, each commercial silkworm Bombyx mori. inherited from different parent 2 n Somatic cells vs germ line cells n 2 n No 2 Precursor progeny n s of future generatio  Sexual reproduction generates genetic diversity If maternal and paternal homologs carry the same genes, why would sexual reproduction produce genetic diversity? llele: Variant version of a gene. Do say two alleles of a gene Gene pool: All genes (ANDnotalleles) 2 genes!within a population. Many number Gene frequency: genes areof multi-allelic! times an allele occur in a gene pool. https://virtualbiologylab.org/ModelsHTML5/PopGenFishbowl/ Extra reading if you like PopGenFishbowl.html Eye color determination 2 major eye color genes and 14 more genes determining the expression of this Sexual reproduction gives organisms a competitive advantage in a changing environment Genetic reshuffling Genetic improvement is conditional Adaptation to a changing environment Extra reading if you like: moth adaptation  2. Meiosis and Fertilization Special cell division in sexually reproducing organisms that reduces the number of chromosomes in gametes Duplicated Homologous Chromosomes Pair During Meiotic Prophase Crossing-Over Occurs Between the Duplicated Maternal and Paternal Chromosomes in Each Bivalent Number of chrs n 2n  Chromosome pairing is key in Meiosis From a cell-biological point of view in mitosis the homologous chromosomes do not pair, they are not in the proper configuration to support crossing over. From a molecular-mechanistic point of view crossing over is usually initiated by a double-strand break (a cut through both chains of the double helix) in one of the interacting partners. The specialized enzymes that make these double strand breaks are not usually expressed during mitosis. Future reading no need to memorise  Notice the similarities and differences Figure 6–31 Homologous reco Chromosome Pairing and Crossing-Over Ensure the Proper Segregation of Homologs Haploid Gametes Contain Reassorted Genetic Information >> Independent Assortment  Independent assortment  2n different haploid gametes (with n different chromosomes)  Here n = 3, and there are 23, or 8  n=23  223  8.388.608 possibilities (Without crossing over)  No two similar organisms Haploid Gametes Contain Reassorted Genetic Information >> Crossing over How many different gametes can you make? ~limitless genetic variations Meiosis Is Not Flawless Nondisjunction ~10% of egg meiosis ~3% of sperm meiosis (cell cycle checkpoint) Aneuploidy = wrong number of chromosomes  MENDEL AND THE LAWS OF INHERITANCE I am convinced that it will not be long before the whole world acknowledges the results of my work. Mendel Disproved the Alternative Theories of Inheritance Mendel Studied Traits That Are Inherited in a Discrete Fashion Characters Traits Mendel Studied Traits That Are Inherited in a Discrete Fashion Advantages of using peas Short generation time Large numbers of offspring Mating could be controlled; self-pollinated cross-pollinated Mendel chose: only those characters that occur in 2 distinct alternative forms (yellow/green for example) plants that were true-breeding (plants that produce offspring of the same variety when they self-pollinate)  Hybridization  Hybridization -> two contrasting, true-breeding varieties  P generation = true- breeding parents  F1 generation = hybrid offspring of the P generation  F2 generation = from F1 individuals self-pollinate or cross-pollinate with other F1 hybrids  Mendel’s 3 laws The Law of Segregation The Law of Independent assortment The Law of Dominance  The Law of Segregation In the 1800s, the explanation of heredity was the “blending” hypothesis Mendels F1 generation were purple Blending hypothesis must be wrong!  The Law of Segregation Mendel crossed the F1 hybrids, >> many of the F2 plants had purple flowers, but some had white >> ratio of about 3 purple to 1 white flower in the F2 generation  The Law of Segregation Mendel reasoned > only purple flower factor affects color in F1 hybrids Mendel called purple flower color a dominant trait white flower color a recessive trait White flower factor not diluted or destroyed because it reappeared in the F2 generation  The Law of Segregation Mendel observed same pattern in 6 other characters each represented by two trait What Mendel called a “heritable factor” is what we now call a gene Notice the ratio! A 3:1 ratio doesn’t mean if there were only 4 offspring's 3 will be different to 1!  Mendel’s Model  Mendel developed a model to explain the 3:1 inheritance pattern in F2 1. Alternative versions of genes (alleles): account for variations in inherited characters resides at a specific locus on a specific chromosome Mendel’s Model + the law of dominance  Mendel developed a model to explain the 3:1 inheritance pattern in F2 1. Alternative versions of genes (alleles): account for variations in inherited characters resides at a specific locus on a specific chromosome 2. Every organism inherits 2 alleles (per character), one from each parent 3. If alleles are different the dominant allele, determines the organism’s appearance the recessive allele, has no noticeable effect on appearance 4. law of segregation: The 2 alleles separate (segregate) at gamete formation end up in different gametes Mendel’s Model  Model explains 3:1 ratio in the F2  Punnett square > Possible combinations of sperm and egg  dominant allele > capital letter >P  recessive allele > lowercase letter >p Video: Mendel’s Cross on Flower Color Mendel’s Model  Model explains 3:1 ratio in the F2  Punnett square > Possible combinations of sperm and egg  dominant allele > capital letter >Y  recessive allele > lowercase letter >y Useful Genetic Vocabulary  Homozygote: organism with two identical alleles for a gene homozygous for the gene controlling that character  Heterozygote: organism with two different alleles for a gene heterozygous for the gene controlling that character  Phenotype: physical appearance (purple)  Genotype: genetic makeup (Pp or PP)  In the example of flower color in pea plants, PP and Pp plants have the same phenotype (purple) but different genotypes Phenotype and Genotype  The Law of Independent Assortment  Law of segregation > followed a single character  F1 is monohybrid Heterozygous for one character  Cross between such heterozygotes is called a monohybrid cross The Law of Independent Assortment  Now 2 characters (color and shape)  Dihybrids in F1 generation, heterozygous for both characters  Dihybrid cross > are the 2 characters independent or dependent? Mendels second law: The Law of Independent Assortment Genes for different traits are sorted separately from one another so that the inheritance of one trait is not dependent on the inheritance of another. The Law of Independent Assortment  Using dihybrid cross, Mendel developed the law of independent assortment  Each pair of alleles segregates independently of any other pair of alleles (during gamete formation) The Law of Independent Assortment  Using dihybrid cross, Mendel developed the law of independent assortment  Each pair of alleles segregates independently of any other pair of alleles (during gamete formation)  Only applies for genes of different chromosomes Or far apart on same chromosome (why?)  What happens to genes close to each other on a chromosome? Genes That Lie on the Same Chromosome Can Segregate Independently by Crossing- Over  Linkage map = genetic map of chromosome based on recombination frequencies  Distances between genes expressed as map units; one map unit = 1% recombination frequency  Map units indicate relative distance and order, not precise locations of genes Genes That Lie on the Same Chromosome Can Segregate Independently by Crossing- Over  Genes far apart on same chromosome > recombination frequency near 50%  Such genes are physically linked, but genetically unlinked, and behave as if found on different chromosomes  Ideas of dominance and interaction Different Alleles can have different function/expression  Ideas of dominance and interaction Allelic interactions Complete dominance Incomplete dominance Co-dominance Dominant allele fully expressed neither allele fully expressed Both allele fully expressed  Ideas of dominance and interaction Sex linked traits Traits that are usually carried on sex chromosomes e.g. Color blindness, hemophilia  Ideas of dominance and interaction Pleiotropy a single gene affects two or more characters Extra reading if you like: genetic cause of sickle cell anemia  Ideas of dominance and interaction Environmen t Effect of epigenetics  Ideas of dominance and interaction Polygenics Traits that are determined by multiple genes Extra reading if you like: genetic relationship between eye or skin colour Mendel’s Law of Segregation Applies to All Sexually Reproducing Organisms A pedigree shows the risks of first-cousin marriages Recessive allele that causes a disease is rare > unlikely that two carriers will meet and mate Consanguineous matings (between close relatives) increases chance that both parents carry same rare allele Most societies and cultures have laws or taboos family members that show the deaf phenotype are indicated against marriages by a blue symbol, those that do not by a gray symbol between close relatives  Example Huntington's disease Example cystic fibrosis EACH OF US CARRIES MANY POTENTIALLY HARMFUL RECESSIVE MUTATIONS MOST MUTATIONS ARE NEUTRAL DELETERIOUS MUTATIONS THAT ARE DOMINANT > FAST ELIMINATION FROM POPULATION RECESSIVE MUTATIONS REMAIN AT LOW FREQUENCY IN POPULATION The Classical Genetic Approach Begins with Random Mutagenesis Can you guess which mutation type is the least likely to be effective? Why? Panel 19–1 (Part 1) Some essentials of classical genetics Genetic Screens Identify Mutants Deficient in Specific Cell Processes Different screen to identify Conditional Mutants Permit the Study of Lethal Mutations Biochemistry 2019 58 (13), 1738-1 DOI: 10.1021/acs.biochem.8b00964  CHAPTER CONTENTS THE BENEFITS OF SEX MEIOSIS AND FERTILIZATION MENDEL AND THE LAWS OF INHERITANCE GENETICS AS AN EXPERIMENTAL TOOL EXPLORING HUMAN GENETICS  Single-nucleotide polymorphisms (SNPs) are points in the genome that differ by a single nucleotide pair between one portion of the population and another SNPs occur everywhere! What their effect is will depend on where they occurred. Coding region  Promoter elements  Introns  Transposons  We all have SNPs!! Genetic drifting: drifting of the frequency of an allele relative to that of the other alleles in a population over time because of chance or random event Natural Variation is an excellent tool to study genetics Genome-wide Association Studies We use Natural variation and SNPs to identify new role for genes Genome-wide Association Studies Can Aid the Search for Mutations Associated with Disease SNP analysis can pin down the location of a mutation that causes a genetic disease Genome-wide association studies identify DNA variations that are significantly more frequent in people with age-related macular degeneration (AMD). 100,000 SNPs in each of 146 people A quantitative trait locus (QTL) is a region of DNA which is associated with a particular phenotypic trait, which varies in degree and which can be attributed Really good for mono-allelic traits  Lecture Slides This concludes the Slide Set for Chapter 19 Essential Cell Biology, Sixth Edition No more MBLS-101 lectures! You survived! Copyright © 2023 by W. W. Norton & Company, Inc.