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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verified elite notetaker
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
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 Calculating gene frequencies under selection Let 1, w1, and22 be the relative ﬁtnesses of1A1,otypes A A1A2, w¯ is the average ﬁtness of the A2A2. population: w¯ =p2w11 + 2pqw12 + 2w 22 The new gep2wy1ic frequen2pqw 1re q A1A1 = 1 w A1A2 = 2 w A2A2 = 22 ¯ w¯ The new allelic frequencies are p2w11 + q2w22 + A1 = pqw12 A2= pqw12 w w Selection Allelic frequency change by Selection 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 similap(1 — s)as p0ast slide gives = 1 — 2sp + 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 0.0 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 What is the relative importance of selection versus mutation for evolution? Selection-mutation balance for a deleterious recessive allele Assume: w11= 1;12 = ;22 = 1-s After selep2wo11+ p⇤ p2w 11+ 2pqw12 + = substituting (1-p) for q: p⇤ p = 1 — s(1 — p2 Selection-mutation balance for a deleterious recessive allele p p⇤ = 1 — s(1 — After mutations occur: (1 — µ)p p0 = (1 — — s(1 — µ)p⇤ = 1 p2 Finally, when mutation and selection are in balance, p′ is equal to p, the frequency of allele A1 that we started with: µ (1 — µ)p = and (1 — p) 2 s and qˆ p = µ = r s Selection-mutation balance for a deleterious dominant allele Assume: w11= 1; w12 = ; 22 = 1-s; here 2 is the dominant allele After selection: p ⇤ = 1 After mutation: p 0= 1 — µ At equilibrium: 1 — µ and qˆ = p = µ • Know example of Medea • Know example of CF and typhoid in humans • Eric can go over these in review Migration Migration: an example Example: Nerodia in Lake Eerie More banded phenotypes on mainland But why hasn’t selection gotten rid of banded types on islands One island model pI= frequency of1Aon island pC = frequency of1Aon continent p 1= (1 — m)p I + where m is the proportion of migrants 0 6pmI = p0 — I by substitution: 6pI = (1 — m)p I + mpC — p I = m(pC — p I ) At equilibrium (ΔpI = 0), A1 will remain constant on the island if there is One island model, speciﬁc to Nerodia pqw 12+ q = frequency of non-banded allele q⇤ q2 w22w = From King & Lawson (1995), we can a11=w12=0.84, and w22=1. pq(0.84) + q⇤ = p2(0.84) + 2pq(0.84) + q2 Substituting (1-q) for p gives: 0.84q + q⇤ 0.84 + = 0.16q2 One island model, speciﬁc to Nerodia If 1% migrate from the continent: 0.84q + ⇤ = 00.84 + 0.99 0.162 The change in q from one generation to the next is: 0.84q + 0.12q q⇤ = q0 — q = 0.99 0.84 + 0.16q 2— q Predictions for q range from 0.64-0.99, depending on assumptions above). Actual value is ~ 0.73. Eﬀects of genetic drift Eﬀects of Genetic Drift 1. Because the fluctuations in allele frequency from one generation to the next are caused by random sampling error, every population follows a unique evolutionary path. 2. Genetic drift has a more rapid and dramatic effect on allele frequencies in small populations than in large populations. 3. Given sufficient time, genetic drift can produce substantial changes in allele frequencies even in populations that are fairly large.
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