1. Genetic Variation & Evolution Chapter 23

2. What you need to know! How mutation and sexual reproduction each produce genetic variation How mutation and sexual reproduction each produce genetic variation

3. Variation Variations exist between individuals in a given population. The following are heritable: Variations exist between individuals in a given population. The following are heritable: Mutation: mostly point mutations (other mutations are possible) Mutation: mostly point mutations (other mutations are possible) Sexual Reproduction: crossing over, independent assortment Sexual Reproduction: crossing over, independent assortment Diploidy: recessive alleles can be hidden (from natural selection) but stay around Diploidy: recessive alleles can be hidden (from natural selection) but stay around

4. Variation Outbreeding: mating with non-related partners increases new allele combinations Outbreeding: mating with non-related partners increases new allele combinations –Behavioral incest is blocked in most higher order species Balanced polymorphism: different phenotypes in a single population propagate natural selection Balanced polymorphism: different phenotypes in a single population propagate natural selection Heterozygous advantage: advantage to heterozygous alleles despite deadly recessive alleles (ex. Sickle cell anemia) Heterozygous advantage: advantage to heterozygous alleles despite deadly recessive alleles (ex. Sickle cell anemia)

5. Variation Hybrid Vigor: superior quality of offspring when crossing highly inbred strains Hybrid Vigor: superior quality of offspring when crossing highly inbred strains Frequency dependent selection: predators form “search images” fitting most common prey phenotypes Frequency dependent selection: predators form “search images” fitting most common prey phenotypes –http://evolution.berkeley.edu/evolibrary/article/happ yface_11 http://evolution.berkeley.edu/evolibrary/article/happ yface_11http://evolution.berkeley.edu/evolibrary/article/happ yface_11 Neutral Variation: no selection pressure for certain phenotypes Neutral Variation: no selection pressure for certain phenotypes Silent Mutations: mutations that do not impact phenotypes (no selection pressure) Silent Mutations: mutations that do not impact phenotypes (no selection pressure)

6. Natural Selection Differential reproductive success of different phenotypes as a result of the interaction with the environment Differential reproductive success of different phenotypes as a result of the interaction with the environment Due to genetic variations certain phenotypes are better or worse adapted Due to genetic variations certain phenotypes are better or worse adapted Survival depends on the adaptations (fitness) Survival depends on the adaptations (fitness) Reproduction depends on survival Reproduction depends on survival

7. Microevolution Def: Natural selection causes changes in relative frequencies of alleles in the gene pool (Hardy Weinberg) Def: Natural selection causes changes in relative frequencies of alleles in the gene pool (Hardy Weinberg) Adaptation means genes are selected to… Adaptation means genes are selected to… –Increase (good) –Decrease (bad) –Stay the same (neutral) Evolution is the accumulation of advantageous traits Evolution is the accumulation of advantageous traits

8. Stabilizing Selection Extreme phenotypes are bad adapatations Extreme phenotypes are bad adapatations Example primate birth weight: Example primate birth weight: –Too small and the baby dies –Too large and the mother dies Draw… Draw…

9. Directional Selection A single extreme adaptation is good A single extreme adaptation is good Example: peppered moths Example: peppered moths Draw… Draw…

10. Diversifying Selection Selection against the common phenotype Selection against the common phenotype Selection for both extremes Selection for both extremes Example: weeds are either very tall (difficult to uproot) or very short (survive lawn mowers) Example: weeds are either very tall (difficult to uproot) or very short (survive lawn mowers)

11. Sexual Selection Selection for sexual phenotypes: Selection for sexual phenotypes: Male competition: fittest male mates most (antlers, horns, body size) Male competition: fittest male mates most (antlers, horns, body size) Female choice: attractiveness and mating behavior Female choice: attractiveness and mating behavior Sexual dimorphism: diifferent appearance of males and females in certain species Sexual dimorphism: diifferent appearance of males and females in certain species

12. Artificial Selection Directional selection carried out by humans Directional selection carried out by humans Humans select a desireable trait and only breed animals with the selected trait (dogs, cats, sheep, horses, cows, etc.) Humans select a desireable trait and only breed animals with the selected trait (dogs, cats, sheep, horses, cows, etc.)

13. Imperfection Natural selection does not fashion the perfect organism because: Natural selection does not fashion the perfect organism because: 1. Selection only edits existing variation 2. Evolution is limited by historical constraints 3. Adaptations are often compromises 4. Change, natural selection and the environment interact

14. Homework Concept Checks 23.1 (pg. 458): Concept Checks 23.1 (pg. 458): 1. What did Mendel’s findings about genetics add to Darwin’s theory of evolution by natural selection? 2. Suppose a population or organisms with 500 gene loci is fixed at half of these loci. How many alleles are found in its gene pool? Explain. 3. Which parts of the Hardy-Weinberg equation (p 2 +2pq + q 2 = 1) correspond to the frequency of individuals that have at least one PKU allele?

15. Homework Concept Checks 23.2 (pg. 460): Concept Checks 23.2 (pg. 460): 1. Of all the mutations that occur, why do only a small fraction become widespread in a gene pool? 2. How does sexual recombination produce variation?

16. Homework Concept Checks 23.3 (pg. 462): Concept Checks 23.3 (pg. 462): 1. In what sense is natural selection more “predictable” than genetic drift? 2. Distinguish genetic drift and gene flow in terms of (a) how they occur and (b) their implications for future genetic variation in a population.

17. Homework Concept Checks 23.4 (pg. 470): Concept Checks 23.4 (pg. 470): 1. Does nucleotide variability in a population always correspond to phenotypic polymorphism? Why or why not? 2. What is the relative fitness of a sterile mule? Explain. 3. How does sexual selection lead to sexual dimorphism? 4. Explain what is meant by the “reproductive handicap” of sex.