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 22 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 7 views. For similar materials see Evolutionary Biology in Biological Sciences at Clemson University.
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Date Created: 07/12/16
Conclusions of H-W equilibrium p 2 + 2pq + q 2 = 1 • Conclusion 1: The allele frequencies in a population will not change, generation after generation. • Conclusion 2: If the allele frequencies in a population are given by p and q, the genotype frequencies will be given by p2, 2pq, and q2. Assumptions of Hardy-Weinberg Equilibrium 1. There is no selection 2. There is no 3. mutation There is 4. no migration There are no chance events (populations 5. are inﬁnitely large) Individuals choose their mates at random Mechanisms of Evolution By providing a set of explicit conditions under which evolution does not happen, the Hardy– Weinberg analysis identiﬁes the mechanisms that can cause evolution in real populations. Chi-squared test 2 test z = ⌃ (oberved— expectected) statistic d degrees of df = k — 1 — freedom m Cutoﬀ for statistical signiﬁcance for 1 degree of freedom is 3.841. Example Is the following population of individuals with the following genotypic frequencies in Hardy-Weinberg equilibrium? Genotyp Frequenc e y A A 35 Aa 48 aa 12 Selection Selection happens when individuals with particular phenotypes survive to sexual maturity at higher rates than those with other phenotypes, or when individuals with particular phenotypes produce more oﬀspring during reproduction than those with other phenotypes. Calculating gene frequencies under selection Let w11, w12, and w22 be the relative ﬁtnesses of genotypes A1A2, and w¯ is the average ﬁtness of the A2A2. population: W stands forw¯itne=p2w 11+ 2pqw12+ q2w22 The new genotypic frequencies are p2w 1 2pqw 1 q A1A 1= A 1A2= 2 A2 A2= 222 1 w w w¯ The new allelic frequencies are p2w11 + q2w22 + A1 = A2= pqw12w pqw12w Selection Allelic frequency change by Selection Selection can change genotype frequencies so that they cannot be calculated by multiplying the allele frequencies. This is an example of over- Can human populations evolve in response to HIV? Eﬀects of lethal recessive alleles Hard if not impossible to get rid of lethal recessive. They ‘hide’ in the Selection on recessive alleles wAA = 1 wAa = 1 waa= 1 — s pqwAa + q0 q2w aaw¯ = pqw Aa + q0 = p2wAA2w+ 2pqAa + q(1 — q0 substitute (1-q) for = sq) 1 p — qq 2 q0 rearrange, s=1 if = 1 + lethal Selection on dominant alleles w AA = 1 — s w Aa = 1 — s w aa= 1 similar logic p0s last slide) 1 — g=ve2sp + s2 substitute 1 for s and lethal dominants are removed in a single generation Selection favoring heterozygotes VV VL LL example of 0.735 1.0 overdominance A 1A1 = 1 — s A 1A2 = 1 A 2A2 = 1 — t t pˆ s + t = stable equilibria with over unstable equilibria with over dominance see Computing consequencese Frequency dependent selection Mutation p’ = p -μp q’ = q+μp mutation typically too small to aﬀect measurable evolutionary Salt tolerance in ﬂies Next time: Mutation-selection balance Migratio n Drift
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