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The Genetic Basis of Evolutionary Change: Simple Traits, Discrete Traits, and Continuous Traits

Explore the genetic basis of evolutionary change, including the frequencies of alleles and genotypes, phenotype frequencies, and factors that can change gene frequencies such as selection, drift, mutation, and migration.

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The Genetic Basis of Evolutionary Change: Simple Traits, Discrete Traits, and Continuous Traits

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  1. THE GENETIC BASIS OF EVOLUTIONARY CHANGE Simple, discrete traits Continuous traits

  2. Evolution: A change in gene frequency

  3. GG BB GB 1 locus, 2 alleles Co-dominant Heterozygote detectable

  4. Phenotypes GG 3 (.25) BB 3 (.25) GB 6 (.50) 12 (1.0) What are the frequencies of the three phenotypes in this population?

  5. 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?

  6. 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%)

  7. 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

  8. 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

  9. 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?

  10. 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

  11. 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 R = 1-r = .5 p2 + 2pq + q2 = 1.0 .25

  12. Gene and genotype frequencies will be the same every generation if the population is Large Randomly mating Not receiving migrants Not undergoing selection IN “HARDY-WEINERG EQUILIBRIUM”

  13. Factors that can change gene frequencies: Selection Drift Mutation Migration

  14. Factors that can change gene frequencies: Selection: Differential reproductive success or reproductive FITNESS

  15. Red leaves fewer offspring relative to Blue time

  16. Blue produces more offpring relative to Red time

  17. Factors that can change gene frequencies: Selection Drift: In small populations, “sampling error” chance fluctuations in reproduction

  18. DRIFT time

  19. Founder effect Time and space

  20. Factors that can change gene frequencies: Selection Drift Mutation : recurrent and directional

  21. Recurrent mutation of R --------> r time

  22. Factors that can change gene frequencies: Selection Drift Mutation Migration: introduction of genes from outside the population.

  23. time

  24. THE GENETIC BASIS OF EVOLUTIONARY CHANGE Simple, discrete traits Continuous traits

  25. Example of disruptive selection: Sexual dimorphism Example of Directional selection: cranial capacity Example of balancing selection: Birth weight

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