1. Population Genetics

2. u The study of genetic variation in populations.

3. Population u A localized group of individuals of the same species.

4. Species u A group of similar organisms. u A group of populations that could interbreed.

5. Gene Pool u The total aggregate of genes in a population. u If evolution is occurring, then changes must occur in the gene pool of the population over time.

6. Microevolution u Changes in the relative frequencies of alleles in the gene pool.

7. Hardy-Weinberg Theorem u Developed in 1908. u Mathematical model of gene pool changes over time.

8. Basic Equation u p + q = 1 u p = % dominant allele u q = % recessive allele

9. Expanded Equation u p + q = 1 u (p + q) 2 = (1) 2 u p 2 + 2pq + q 2 = 1

10. Genotypes u p 2 = Homozygous Dominants 2pq = Heterozygous q 2 = Homozygous Recessives

11. Example Calculation u Let’s look at a population where: u A = red flowers u a = white flowers

13. Starting Population u N = 500 u Red = 480 (320 AA+ 160 Aa) u White = 20 u Total Genes = 2 x 500 = 1000

14. Dominant Allele u A = (320 x 2) + (160 x 1) = 800 = 800/1000 A = 80%

15. Recessive Allele u a = (160 x 1) + (20 x 2) = 200/1000 =.20 a = 20%

16. A and a in HW equation u Cross: Aa X Aa u Result = AA + 2Aa + aa u Remember: A = p, a = q

17. Substitute the values for A and a u p 2 + 2pq + q 2 = 1 (.8) 2 + 2(.8)(.2) + (.2) 2 = 1.64 +.32 +.04 = 1

18. Dominant Allele u A = p 2 + pq =.64 +.16 =.80 = 80%

19. Recessive Allele u a = pq + q 2 =.16 +.04 =.20 = 20%

20. Result u Gene pool is in a state of equilibrium and has not changed because of sexual reproduction. u No Evolution has occurred.

21. Importance of Hardy-Weinberg u Yardstick to measure rates of evolution. u Predicts that gene frequencies should NOT change over time as long as the HW assumptions hold. u Way to calculate gene frequencies through time.

22. Example u What is the frequency of the PKU allele? u PKU is expressed only if the individual is homozygous recessive (aa).

23. PKU Frequency u PKU is found at the rate of 1/10,000 births. u PKU = aa = q 2 q 2 =.0001 q =.01

24. Dominant Allele u p + q = 1 p = 1- q p = 1-.01 p =.99

25. Expanded Equation u p 2 + 2pq + q 2 = 1 (.99) 2 + 2(.99x.01) + (.01) 2 = 1.9801 +.0198 +.0001 = 1

26. Final Results u Normals (AA) = 98.01% u Carriers (Aa) = 1.98% u PKU (aa) =.01%

27. AP Problems Using Hardy-Weinberg u Solve for q 2 (% of total). u Solve for q (equation). u Solve for p (1- q). u H-W is always on the national AP Bio exam (but no calculators are allowed).

28. Hardy-Weinberg Assumptions 1. Large Population 2. Isolation 3. No Net Mutations 4. Random Mating 5. No Natural Selection

29. If H-W assumptions hold true: u The gene frequencies will not change over time. u Evolution will not occur. u But, how likely will natural populations hold to the H-W assumptions?

30. Microevolution u Caused by violations of the 5 H-W assumptions.

31. Causes of Microevolution 1. Genetic Drift 2. Gene Flow 3. Mutations 4. Nonrandom Mating 5. Natural Selection

32. Genetic Drift u Changes in the gene pool of a small population by chance. u Types: u 1. Bottleneck Effect u 2. Founder's Effect

33. By Chance

34. Bottleneck Effect u Loss of most of the population by disasters. u Surviving population may have a different gene pool than the original population.

36. Result u Some alleles lost. u Other alleles are over- represented. u Genetic variation usually lost.

37. Importance u Reduction of population size may reduce gene pool for evolution to work with. u Ex: Cheetahs

38. Founder's Effect u Genetic drift in a new colony that separates from a parent population. u Ex: Old-Order Amish

39. Result u Genetic variation reduced. u Some alleles increase in frequency while others are lost (as compared to the parent population).

40. Importance u Very common in islands and other groups that don't interbreed.

41. Gene Flow u Movement of genes in/out of a population. u Ex: u Immigration u Emigration

42. Result u Changes in gene frequencies.

43. Mutations u Inherited changes in a gene.

44. Result u May change gene frequencies (small population). u Source of new alleles for selection. u Often lost by genetic drift.

45. Nonrandom Mating u Failure to choose mates at random from the population.

46. Causes u Inbreeding within the same “neighborhood”. u Assortative mating (like with like).

47. Result u Increases the number of homozygous loci. u Does not in itself alter the overall gene frequencies in the population.

48. Natural Selection u Differential success in survival and reproduction. u Result - Shifts in gene frequencies.

49. Comment u As the Environment changes, so does Natural Selection and Gene Frequencies.

50. Result u If the environment is "patchy", the population may have many different local populations.

51. Genetic Basis of Variation 1. Discrete Characters – Mendelian traits with clear phenotypes. 2. Quantitative Characters – Multigene traits with overlapping phenotypes.

52. Polymorphism u The existence of several contrasting forms of the species in a population. u Usually inherited as Discrete Characteristics.

53. Examples Garter SnakesGaillardia

54. Human Example u ABO Blood Groups u Morphs = A, B, AB, O

55. Other examples

56. Quantitative Characters u Allow continuous variation in the population. u Result – u Geographical Variation u Clines: a change along a geographical axis

57. Yarrow and Altitude

58. Sources of Genetic Variation u Mutations. u Recombination though sexual reproduction. u Crossing-over u Random fertilization

59. Preserving Genetic Variation 1. Diploidy - preserves recessives as heterozygotes. 2. Balanced Polymorphisms - preservation of diversity by natural selection.

60. Example u Heterozygote Advantage - When the heterozygote or hybrid survives better than the homozygotes. Also called Hybrid vigor.

61. Result u Can't bred "true“ and the diversity of the population is maintained. u Ex – Sickle Cell Anemia

62. Comment u Population geneticists believe that ALL genes that persist in a population must have had a selective advantage at one time. u Ex – Sickle Cell and Malaria, Tay-Sachs and Tuberculosis

64. Fitness - Darwinian u The relative contribution an individual makes to the gene pool of the next generation.

65. Relative Fitness u Contribution of one genotype to the next generation compared to other genotypes.

66. Rate of Selection u Differs between dominant and recessive alleles. u Selection pressure by the environment.

67. Modes of Natural Selection 1. Stabilizing 2. Directional 3. Diversifying 4. Sexual

68. Stabilizing u Selection toward the average and against the extremes. u Ex: birth weight in humans

69. Directional Selection u Selection toward one extreme. u Ex: running speeds in race animals. u Ex. Galapagos Finch beak size and food source.

71. Diversifying u Selection toward both extremes and against the norm. u Ex: bill size in birds

73. Comment u Diversifying Selection - can split a species into several new species if it continues for a long enough period of time and the populations don’t interbreed.

75. Sexual Mate selection u May not be adaptive to the environment, but increases reproduction success of the individual.

76. Result u Sexual dimorphism. u Secondary sexual features for attracting mates.

77. Comments u Females may drive sexual selection and dimorphism since they often "choose" the mate.

78. The Origin of Species

79. Biological Species u A group of organisms that could interbreed in nature and produce fertile offspring.

80. Key Points u Could interbreed. u Fertile offspring.

81. Speciation Requires: 1. Variation in the population. 2. Selection. 3. Isolation.

82. Reproductive Barriers u Serve to isolate a populations from other gene pools. u Create and maintain “species”.

83. Modes of Speciation 1. Allopatric Speciation 2. Sympatric Speciation Both work through a block of gene flow between two populations.

85. Allopatric Speciation u Allopatric = other homeland u Ancestral population split by a geographical feature. u Comment – the size of the geographical feature may be very large or small.

86. Example u Pupfish populations in Death Valley. u Generally happens when a specie’s range shrinks for some reason.

87. Another Example

88. Conditions Favoring Allopatric Speciation 1. Founder's Effect - with the peripheral isolate. 2. Genetic Drift – gives the isolate population variation as compared to the original population.

89. Conditions Favoring Allopatric Speciation 3. Selection pressure on the isolate differs from the parent population.

90. Result u Gene pool of isolate changes from the parent population. u New Species can form.

91. Comment u Populations separated by geographical barriers may not evolve much. u Ex - Pacific and Atlantic Ocean populations separated by the Panama Isthmus.

92. Examples u Fish - 72 identical kinds. u Crabs - 25 identical kinds. u Echinoderms - 25 identical kinds.

93. Adaptive Radiation u Rapid emergence of several species from a common ancestor. u Common in island and mountain top populations or other “empty” environments. u Ex – Galapagos Finches

94. Mechanism u Resources are temporarily infinite. u Most offspring survive. u Result - little Natural Selection and the gene pool can become very diverse.

95. When the Environment Saturates u Natural Selection resumes. u New species form rapidly if isolation mechanisms work.

96. Sympatric Speciation u Sympatric = same homeland u New species arise within the range of parent populations. u Can occur In a single generation.

98. Plants u Polyploids may cause new species because the change in chromosome number creates postzygotic barriers.

99. Polyploid Types 1. Autopolyploid - when a species doubles its chromosome number from 2N to 4N. 2. Allopolyploid - formed as a polyploid hybrid between two species. u Ex: wheat

100. Autopolyploid

101. Allopolyploid

102. Animals u Don't form polyploids and will use other mechanisms.

103. Gradualism Evolution u Darwinian style evolution. u Small gradual changes over long periods time.

104. Gradualism Predicts: u Long periods of time are needed for evolution. u Fossils should show continuous links.

105. Problem u Gradualism doesn’t fit the fossil record very well. (too many “gaps”).

106. Punctuated Evolution u New theory on the “pacing” of evolution. u Elridge and Gould – 1972.

107. Punctuated Equilibrium u Evolution has two speeds of change: u Gradualism or slow change u Rapid bursts of speciation

108. Predictions u Speciation can occur over a very short period of time (1 to 1000 generations). u Fossil record will have gaps or missing links.

110. Predictions u New species will appear in the fossil record without connecting links or intermediate forms. u Established species will show gradual changes over long periods of time.

111. Possible Mechanism u Adaptive Radiation, especially after mass extinction events allow new species to originate. u Saturated environments favor gradual changes in the current species.

112. Comment u Punctuated Equilibrium is the newest ”Evolution Theory”. u Best explanation of fossil record evidence to date.

113. Evolutionary Trends u Evolution is not goal oriented. It does not produce “perfect” species.

115. Future of Evolution ? u Look for new theories and ideas to be developed, especially from new fossil finds and from molecular (DNA) evidence.