17.1 Genes and Variation

1. 17.1 Genes and Variation

2. Remember: Genotype: exact set of alleles in an organism (genetics) (Aa) Phenotype: physical characteristics (appearance) (Red) Which does natural selection act on?

3. Natural selection acts on phenotype! Some phenotypes better suited to current environment, therefore have greater fitness. Nat Selection -> phenotype -> genotype

4. Organisms with a higher fitness pass on more of their genes to the next generation of the species.

5. Gene pool - all alleles present in an entire population of an organism

7. What’s wrong with the reasoning here?

8. Allele frequency - percentage of certain allele in the gene pool.

9. Need to know genotype to see allele frequency

10. Evolution = change in frequency of alleles in a population over time

11. Individuals do not evolve in their lifetime. (you keep same alleles) • Populations evolve through MANY generations. (allele frequencies change)

12. STOP DAY 1

13. Input - 4/16/13 3 Sources of Genetic Variation

14. 1) Mutation - change in DNA may affect phenotype (can happen in germ line cells and affect offspring)

15. 2) Sexual Reproduction - creates new combinations of genetics in gametes

16. 3) Lateral Gene Transfer - swapping of genetic material from one organism to another (usually prokaryotes)

17. Stop Day 2

18. Single gene traits - phenotype controlled by only one gene Ex) Bands in snails (BB - banded, bb - no bands Bb - )

20. Polygenic Trait - phenotype affected by multiple genes - More than two phenotypes possible

22. 17.2 Evolution as Genetic Change

23. Single Gene Traits - one phenotype has stronger fitness and certain allele increases frequency across generations • BB = black bb = red Bb = brown

24. Natural Selection on Polygenic Traits

25. 1) Directional Selection - one end of curve has greater fitness, population shifts, increasing that end

27. 2) Stabilizing Selection - indiv. in middle have greater fitness

29. 3) Disruptive Selection - indiv on both outer ends have greater fitness

33. Disruptive Selection can lead to Speciation - 2 new species!

34. Stop Day 3

35. 17.2 Other Factors driving Evolution Genetic Drift - change in allele frequency over time (brought about by chance, not selection)

36. Genetic Drift - some indiv. in a population happen to have more offspring - the alleles in those organisms become more common in the gene pool

37. Genetic Drift - some indiv. in a pop. have less offspring - the alleles in those organism become less common in the gene pool

38. Genetic Bottleneck - reduction of population

39. Genetic Bottleneck - may drastically alter allele frequency

41. Toba Supervolcano • 70,000 YA - may have reduced human population to 10,000 (bottleneck)

43. Founder Effect - when only a few individuals colonize a new habitat

44. Founder Effect - reduces gene pool in new population • Ex) Dutch that colonized South Africa have high rates of Huntington’s Disease

45. Genetic Equilibrium (balance) - pop. is not evolving, allele frequency is unchanging

46. Genetic Equilibrium requires: • Large population size • Random mating - no natural or artificial selection • No immigration or emigration • No mutations Are humans in genetic equilibrium?