Evolutionary Biology BIO 3350 Clemson
Evolutionary Biology BIO 3350 Clemson 12050 - BIOL 3350 - 001
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12050 - BIOL 3350 - 001
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This 34 page Class Notes was uploaded by Emily Emmons on Tuesday July 12, 2016. The Class Notes belongs to 12050 - BIOL 3350 - 001 at Clemson University taught by Dr. Michael Sears in Fall 2016. Since its upload, it has received 5 views. For similar materials see Evolutionary Biology in Biological Sciences at Clemson University.
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Date Created: 07/12/16
Probability of ﬁxation If genetic drift is the only evolutionary process at work, eventually one allele will drift to a frequency of 1 and all other alleles will be lost. Genetic drift leads to a loss of heterozygosity Loss across generations Heterozygosity is the frequency of heterozygotes in a population. Drift in 107 populations of 16 ﬂies Heterozygosity lost across generations • Note, H is maximized when p=q=0.5 • Why is there a mismatch between the fit for the actual number of flies flies used in the experiments? Eﬀective population size drives drift Not the census (actual) size for example: 5 males and 5 females= 10 1 male a 9 females= 3.6 What are the consequences of effective population size on drift? Random Fixation and Loss of Heterozygosity in Natural Populations Genetic polymorphism, the fraction of loci within the genome that have at least two alleles with frequencies higher than 0.01, increased with population size in nature. …as did number of alleles per locus. Young et al. 1996 What is the rate of evolution if only genetic drift is at work? The rate of evolution, here, is the rate at which new alleles created by mutation are substituted for other alleles already present. The rate of evolution is equivalent to the mutation rate v is the rate of neutral mutations Selections versus neutral processes When mutation, genetic drift, and selection interact, three processes occur: (1) Deleterious alleles appear and are eliminated by selection; (2) Neutral mutations appear and are fixed or lost by chance; and (3) Advantageous alleles appear and are swept to fixation by selection. The relative importance of (2) and (3) in determining the overall substitution rate is a matter of debate. When populations are subject to both selection and genetic drift, smaller populations follow more diverse evolutionary paths. Just how large an advantage or liability must an allele carry, in a population of a given size, for selection to overcome drift and play a role in determining the allele's fate? Neutral theory as a null model when replacements are deleterious when replacements are neutral when replacements are advantageous The neutralist–selectionist controversy is a debate about the relative importance of drift and positive selection in explaining molecular evolution. Nonrandom mating Inbreeding decreases the frequency of heterozygotes and increases the frequency of homozygotes compared to expectations under Hardy–Weinberg assumptions. but doesn’t change allele frequencies…no evolution F: the probability that the two alleles in an individual are identical by descent (meaning that both alleles came from the same ancestor allele in some previous generation). and Calculating F half-sib parents full-sib parents Inbreeding depression negatively affects offspring, likely due to increased numbers of homozygous recessives Inbreeding depression negatively affects offspring, likely due to increased numbers of homozygous recessives Extinction vortex