Evolution: Week Five
Evolution: Week Five BIO318
Virginia Commonwealth University
Popular in Biology: Evolution and Biodiversity
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This 6 page Class Notes was uploaded by Jayda Abrams on Saturday October 1, 2016. The Class Notes belongs to BIO318 at Virginia Commonwealth University taught by Dr. Turbeville in Fall 2016. Since its upload, it has received 10 views. For similar materials see Biology: Evolution and Biodiversity in Biology at Virginia Commonwealth University.
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Date Created: 10/01/16
Week Five Tuesday 9/27/16 and Thursday 9/29/16 1 2 Homo + 2 Hetero = 2(number of individuals) OR take the average P and the average Q to get 2pq. This means the observed frequency of heterozygotes is at best the same or less than the expected. What is the reason heterozygotes might be less than expected? Inbreeding or any kind of non-random mating. FST F = 0 = no inbreeding F=1 = all inbreeding FST = 0 = observed and experimental are equal. Two local populations act like one big population randomly mating (In the picture this is represented with just the dark blue box). FST = 1 = each population is different. Local mating/inbreeding. If all P’s are equalSTwill equal zero FST is the most popular measure in population genetics after heterozygosity. FST is just another way to talk about inbreeding in multiple populations Neutral Theory Combination of selection and genetic drift also involves mutation but not assumed Selection is biased to eliminate less fit alleles- this is called purifying selection Assume all selection is purifying selection on highly deleterious (= not advantageous/ bad) mutations All other mutations have no effect on fitness Neutral Theory of Molecular Evolution (NTME) says: Most variations seen are neutral Most substitutions even those that change proteins are neutral Substitutions- a fixed difference among populations and/or species. Evidence…: 1. No change in protein sequence (20 different amino acids) 2. Proteins usually can be thought of as falling in a region of very important to a region of not very important. 3. Genome don’t just produce proteins. Substitution in noncoding DNA regions of genome without genes would be neutral. N es subject to genetic drift. What happens if the mutation rate changes? You can no longer do Kv and would have to take the average. 21eKv = mutation rate for the population in a diploid population. = Probability of new mutation fixing due to genetic drift. 2???????? How species accumulate difference is equal to the substation rate. Implies constant rate of change. Then should be a linear connection between time passed and how genetically different one is from the starting ancestor. Neutral Theory started bases for molecular clock. Molecular Clock- Rate of molecular divergence will be linearly related to time only under certain mutation models. Finite sites no Saturation- Mutations happen at sites that previously had mutations, so that the relationship between time (x) and divergence (y, # base pair differences) is not linear. Undercounting the number of substitutions makes a graph look like a plateau is occurring. Infinite number of sites reduces saturation. How do we know how long ago species diverged? Fossils. What if you don’t have fossils? Use the molecular clock and work backwards. Extension of the NTME N eas no effect on substitution rates in the NTME. Assumptions: Equilibrium is no longer applied Mutations are bad, but do not kill you Null Model with NTME If the null theory is true sub/site at synonymous sites = sub/site at non- synonymous sites. This is because there are no fitness differences. (POS mutations would benefit from mutation and it would become fit) Ka = Synonymous Ks = nonsynonymous Purifying selection- numerator is smaller than the denominator and the ratio is less than one. Polygenetic trait- trait controlled by many genes Infinitesimal Model- traits to determine by infinity number of loci. Each have a small effect but put together they have a big effect. When polygenetic traits are passed down this is known as multi-factorial. Additive Genetic Effect- Gradation in phenotype. Effect of alleles at loci added together to get effects on loci. Non Additive Effect- Anything not additive is non additive. Recessive and Dominant- Single locus, non-additive effect Epistasis- Expression of one gene can affect the expression of another gene Epistasis Expression of one gene masks/modifies effect of another gene pair Gene masks phenotypic effects of another gene Each step of development increases complexity of organ Under control and influence of many genes Anything other than additive means you are not working with additive genetic effects! Latent Variation- Refers to variation produced through selection and re- assortment of alleles at many loci. A. There is no new variation of offspring different from the parent generations. B. There are many ways that genes can be put together and not all combinations have been used the second generation exceeds the parents. Haplotypes- Combinations of alleles in more than one gene come together. Knowing the genotype at each locus and the frequency of this genotype in a population, however, does not tell you anything about the haplotype. Linkage Disequilibrium- Independence (ex: you when you turned 18) Because it is independent you use and. And Multiply
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