Biology 212 Chapter 23 The Evolution of Populations

1. Biology 212 Chapter 23The Evolution of Populations

2. You will be able to… • Explain terms gene pooland genotype / phenotype frequency • Describe the purpose of the • Hardy-Weinberg principle • Calculate evolutionary D using • H-W principle’s equation • Elaborate on factors that cause genetic • variations in populations: Natural selection, • genetic drift, & gene flow

3. Quick review of terms used in genetics: • Allele: a variation of a gene • e.g. tall pea plant / short pea plant • Phenotype: How alleles express themselves • (physically, chemically, behaviorally) • Genotype: combination of alleles • e.g. dominant and / or recessive arrangements

4. Quick review of terms used in genetics: • Genotype: • Homozygous recessive: • 2 recessive alleles; one from each parent • e.g. aa • Homozygous dominant: • 2 dominant alleles; one from each parent • e.g. AA • Heterozygous (hybrid): • Mixed alleles – 1 dominant / 1 recessive • e.g. Aa

5. Population’s gene pool • Allalleles for all loci present in a population • Large gene pool = large variety • Diploid organisms have a maximum of • two different alleles at each gene locus.

6. Individualshave a small fraction of allele variety present in a population’s gene pool. e.g. Hair color: black, brown, blonde, red alleles One person only 2 combos possible.

7. One definition of Evolution is: D in frequencies of allelesin gene pool of a population. • Evolution involves individuals’ genotypes, but actual D observed at _________________ level many generations. • Observe allele frequencies & how they vary in response to __________________ ______________________________

8. Genotypefrequenciesfor all 1000 individualsof a hypothetical population 49% 42% 9% 100% Note: Heterozygous (Aa) genotype is a separate group

9. Phenotypefrequencies for all 1000 individualsof a hypothetical population 91% 9% 100% Note: Heterozygous genotype (Aa) will count as ________________________

10. 490 AA = 980 dominant A alleles + 420 Aa = 420 dominant A alleles Total = 1400 A alleles in the population of 1,000 individuals.

11. 420 Aa = 420 recessive a alleles + 90 aa = 180 recessive a alleles Total = 600 a alleles Note:

12. Allele frequencies for all 1000 individualsof a hypothetical population 70% 30% 100% No matter # of individuals, Frequency still has to add up to

13. Hardy-Weinberg Principle • Explains stability of successive • generations’ gene pool frequencies • in populations at genetic equilibrium Essential to understanding mechanisms of evolutionary change

14. 1. Random mating • 2. No net mutations Genetic equilibrium requires: • 3. Large population size • 4. No migration in or out (no gene flow) 5. No natural selection 6. Everyone breeds and produces same # of offspring

15. Hardy-Weinberg principle: • If a population is large, process of inheritancealone doesn’t cause D’s in allele frequencies • Populations can be in Hardy-Weinberg equilibrium for some loci, and show evolution in other loci.

16. p = frequency of dominant allele Hardy-Weinberg equation: • q = frequency of recessive allele • p + q = 1 • if you know q,

17. An equation used to: discover probable genotype frequencies in a population track allele frequency changes from one generation to another Hardy-Weinberg equation:

18. p2 + 2pq + q2 = 1 Genotype frequencies of a population are described by the relationship: • p2 is frequency of __________________ ______________ genotype • 2pq is frequency of ________________ __________ genotype q2 is frequency of ___________________ ____________ genotype

19. Comparing one generation to next determines if evolution occurred, in what direction, and rate for the selected trait Segregation of alleles and random fertilization

20. Rule of Multiplication for Probability • p2: probability of two of same dominant alleles occurring is p x p • q2: probability of two of same recessive alleles occurring is q x q • 2pq : probability of one p and one q allele occurring is p x q and q x p • (two different possible parental combos)

21. Genotype and allele frequencies

22. Microevolution: Inter-generational changes in genotype (allele) frequencies within a population. • Often involves relatively small or • minor changes, • usually over a few generations (small time increments).

23. Changes in allele frequencies of a population caused by microevolutionary processes:

24. Nonrandom mating: Inbreeding (also self-fertilization) • Inbreeding depression: reduces fitness • Assortative mating: • select similar phenotypes for mating

25. Assortative Mating

26. Nonrandom mating: • Both of these increase frequencyof homozygousgenotypes:

27. Mutation

28. Mutation DNA structure altered by radiation, chemicals, viruses, “jumping genes” (transposons) or errors in replication _____________ genetic variability Which is then acted upon by _________________________ forces

29. RandomD in allele frequencies of a small population: Genetic drift

30. Decreasesgenetic variation within a population • D’s it causes are due to _____________ • not adaptive Genetic drift

31. Genetic drift Decreases variety in a population • Bottleneck: • sudden decrease in population size caused by adverse environmental factors. • Founder effect: • small population colonizes a new area

32. Founder effect: Lake Maracaibo region and Huntington's disease Maria Concepción Soto arrived in 19th century Had unusually large # of descendants “Founder" of population of ~ 20,000 people Huntington’s gene

33. Old Order Amish people of Lancaster County, Pennsylvania e.g. Dwarfism, Ellis-van Creveld syndrome, microcephalism, and polydactylism

34. Founder Effect: Galapagos finches The splitting of a population followed by subsequent evolution is known as _______________ ___________

35. Galapagos finches • Molecular analysis shows: • Galapagos finches are _____________________ • Founding species is a warbler finch • (Certhideaolivacea) found on S. American mainland.

36. Bottlenecking Cheetahs: almost genetically identical Drastic reduction during ice age Reduced again: modern hunting Northern elephant seals: Reduced to 20 individuals Today population > 30,000

37. Gene flow • Movement of alleles caused by _______________________ (not seasonal) btwn populations • Causes D’s in allele frequencies • _________________________ • Introduces new alleles into a population without

38. Natural selection • Causes D’s in allele frequencies • leading to adaptation • Operates on an organism’s

39. Natural selection • D’s genetic composition of a population • Generally most rapid & dramatic evolution is • due to

40. Stabilizing • Favors _____________ – population • Well adapted to an environment • Directional: shifts phenotype • Favors • Disruptive (rare) • Favors Modes of selection

41. (a) No selection (b) Stabilizing selection

42. Extremes are favored Shifts to one end of variation (d) Disruptive selection (c) Directional selection

43. Stabilizing selection e.g. Siberian Husky is a medium-sized, but strong, snow dog. Human baby head size. Why?

44. Arctic critters: white coat favored by the snowy environment

45. Disruptive selection:Drastically alters environmental conditions Extreme traits may be favored over average Giant asteroid collision Indian ocean tsunami

46. Disruptive selection Black-bellied seed cracker finches: Small billed or Large billed birds.

47. Genetic variation in populations: • Mutation (genetic mechanism unknown to Darwin) • Sexual reproduction New phenotypes develop that natural selection can then act upon

48. Genetic polymorphism: Methods of evaluating genetic variation: • Balanced polymorphism:

49. Neutral variation: Methods of evaluating genetic variation: • Geographic variation:

50. Genetic polymorphism:source of external / internal phenotype variation