Lecture 20 Outline of Last Lecture I. Evolution a. Definitions and Preconditions i. Common Misconceptions b. Artificial Selection i. Domestication Syndrome Outline of Current Lecture c. Genetic Variation i. Examples of Allele Diversity ii. Sources of Genetic Variation iii. Measuring Genetic Diversity Current Lecture Evoultion II Finishing Artificial Selection **Clicker Question** All of the following preconditions for evolution by natural selection hold true for evolution by artificial selection except what? -they all hold true because there is a difference in artificial selection — you don’t let all of them breed -example = with foxes, only the aggressive ones and docile ones were chosen to reproduce and the ones in the middle were not -so it does lead to differences in lifetime reproductive success because of whether certain organisms are allowed to breed or not -this is technically not a precondition though — but they all hold true for artificial selection and natural selection **Clicker Question** Bio 152 1st EditionThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute. !Edited with the trial version of Foxit Advanced PDF EditorTo remove this notice, visit:www.foxitsoftware.com/shoppingWith careful selective breeding do you think you’d be able to breed a wolf from a chihuahua? (assume chihuahuas are descended from wolves) Think about what happens to the genome (alleles and genes) during selection -No. You couldn’t select just with the chihuahua, you would have to bring in more genetic variation -the wolf (ancestor) had a very diverse gene pool, humans selected for a very specific gene pool -some genes may have been lost, and over time the genetic diversity is lost (chihuahua has less diversity than a wolf does) example: 3 alleles for digesting alcohol, one works poorly and if you selected against that then that allele would eventually go away, and so you wouldn’t have the other two alleles disappear and so the gene would still be present Genetic Variation A precondition for evolution is that there is genetic variation (NOT phenotypic variation) -pictures on this slide are showing phenotypic variation (facial phenotypes) which is not the same thing -can be genotypic variation in two organisms that look exactly the same Examples of Allele Diversity -shown in the alcohol example above -have a single gene that is functional in your liver, and it is present in three ALLELES -different races tend to have different alleles in this case -one allele works very poorly The total alleles available in a population are its “gene pool” •Ta s m a n i a n d e v i l s -have very little genetic diversity, and its hard to tell them apart molecularly -tumor on Tasmanian devil’s face is contagious because of this (have same immune system) and they bite each other’s faces and pass on the tumors that kill them **Clicker Question** •Heterozygosity is the likelihood of a difference at a particular base pair. What do these data suggest? A higher number means more likelihood of a difference, a lower number means less likelihood that there will be a difference I. Humans are genetically very diverse II. Sumatran orangutans are the most diverse apes III. Chimps are less diverse than humans IV. Bonobos and western chimps are more closely related than the western and eastern chimps •II is the only one that’s true •non african humans are the least diverse•bonobos and western chimps last common ancestor is Pan, while western and eastern chimps have a common ancestor before all of the chimps share Pan, the common ancestor with Bonobos **Clicker Question** •Genetic variability may be seen in phenotype but variability is the number of different alleles for any given gene/sequence — protein coding or not. What could account for the dramatic difference in chimp and human allele frequencies? A. A population collapse in humans B could be true, but there are billions of humans and nowhere near that many chimps •thought that roughly 70,000 years ago there was a dramatic collapse in the human population that led to our low genetic diversity Which population is probably best equipped to survive a new virus? Meaning which population is more likely to have some immunity? -Sumatran orangutans -have more diversity so a larger reservoir of potential immunity than less diverse organisms Sources of Genetic Variation: 1. Mutation: must be a germ line mutation 2. Remember that somatic mutations make no difference - somatic = anything not in the germ line, so if you have a mutation in a cell in your pancreas that doesn’t get passed on to offspring (cancer etc.) 3. Recombination during meiosis 4. A single gene could get changed, or the promoter region (meaning the gene is expressed more or less) 5. Migration: could have two populations, someone moves from one to the other creating more diversity 6. outcrossing with other species (european humans crossbred with neanderthals thousands of years ago) All of these make alleles (different versions of a gene) Mutations can be harmful, beneficial, neutral -positive = lactase persistence (ability to digest lactose) -Positive = human salivary amylase (many apes can’t break starches into sugar in their mouths, which is the reason carbs taste sweet) -usually neutral = alu element (mobile genetic elements that move around a population and using these allows you to do DNA fingerprinting) Measuring Genetic Diversity -map showing distribution of HBS (allele causing sickle cell anemia) **Clicker Question** In northern Angola the allele frequency for Hbs is 18.18%, does this mean that 18% of the population suffers from severe sickle cell anemia? - no- normal allele is Hba, so some people will be homozygous for the normal allele, some heterozygous with Hba and Hbs and some homozygous for the mutated allele Hbs Population of butterflies has the following genotype frequencies: 45% AA, 35% Aa, 20% aa. If you assume a population of 100, how many total copies of the gene are there (how many alleles?) -if you have 100 organisms, each one has a chromosome from mom and one from dad. Each organism has 2 alleles each, and if 100 organisms each have 2 alleles then there will be 200 alleles in the