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THE GENETIC BASIS OF EVOLUTIONARY CHANGE 1. Simple, discrete traits 2. Continuous traits Evolution: A change in gene frequency GG BB GB 1 locus, 2 alleles Co-dominant Heterozygote detectable Phenotypes GG 3 (.25) BB 3 (.25) GB 6 (.50) 12 (1.0) What are the frequencies of the three phenotypes in this population? Phenotypes Genotypes GG 3 3 (.25) BB 3 3 (.25) GB 6 6 (.25) 12 12 (1.0) What are the frequencies of the three genotypes in this population? Phenotypes Genotypes GG 3 3 BB 3 3 GB 6 6 12 12 What are the frequencies of the two alleles or genes in this population? How many G’s? 12 (50%) How many B’s? 12 (50%) Hardy-Weinberg p = frequency of one of the alleles (the dominant one, if there is dominance) q = frequency of the other allele (recessive, if there is recessiveness) p + q = 1.0 p (G) = 0.5 q (B) = 0.5 0.5 + 0.5 = 1.0 The relationship between gene frequencies and genotype frequencies p + q = 1.0 GG + GB + BB = 1.0 p2 + 2pq + q2 = 1.0 .25 + .50 + .25 = 1.0 Red heads is caused by the recessive gene r What are the phenotype frequencies of people with red and blue heads? Red: .25 Blue: .75 Genotype frequencies? RR Rr rr: 25 How do we find the frequencies for RR and Rr? The relationship between gene frequencies and genotype frequencies p + q = 1.0 GG + GB + BB = 1.0 p2 + 2pq + q2 = 1.0 .25 + .50 + .25 = 1.0 If you know what q2, or rr, is, you can solve the others Red heads is caused by the recessive gene r What are the phenotype frequencies of people with red and blue heads? Red: .25 Blue: .75 Genotype frequencies? RR: .25 Rr: .50 rr: .25 r = = .5 .25= .5 R = 1-r p2 + 2pq + q2 = 1.0 Gene and genotype frequencies will be the same every generation if the population is 1. Large 2. Randomly mating 3. Not receiving migrants 4. Not undergoing selection IN “HARDY-WEINERG EQUILIBRIUM” Factors that can change gene frequencies: 1. Selection 2. Drift 3. Mutation 4. Migration Factors that can change gene frequencies: 1. Selection: Differential reproductive success or reproductive FITNESS Red leaves fewer offspring relative to Blue time Blue produces more offpring relative to Red time Factors that can change gene frequencies: 1. Selection 2. Drift: In small populations, “sampling error” chance fluctuations in reproduction DRIFT time Founder effect Time and space Factors that can change gene frequencies: 1. Selection 2. Drift 3. Mutation : recurrent and directional Recurrent mutation of R --------> r time Factors that can change gene frequencies: 1. Selection 2. Drift 3. Mutation 4. Migration: introduction of genes from outside the population. time THE GENETIC BASIS OF EVOLUTIONARY CHANGE 1. Simple, discrete traits 2. Continuous traits Example of disruptive selection: Sexual dimorphism Example of Directional selection: cranial capacity Example of balancing selection: Birth weight