Population genetics is the study of genetic variation within populations. A population's gene pool contains all the alleles of all individuals. Under Hardy-Weinberg equilibrium, allele frequencies remain constant between generations if there is no mutation, migration, genetic drift, or natural selection. Five agents cause evolution: mutation, gene flow, genetic drift, nonrandom mating, and natural selection, which is the only mechanism that leads to adaptation. Natural selection maintains genetic variation and can preserve polymorphisms through mechanisms like heterozygote advantage.

1. Population Genetics

6. Modern Evolutionary Thought

11. Allele Frequencies Define Gene Pools As there are 1000 copies of the genes for color, the allele frequencies are (in both males and females): 320 x 2 (RR) + 160 x 1 (Rr) = 800 R; 800/1000 = 0.8 (80%) R 160 x 1 (Rr) + 20 x 2 (rr) = 200 r; 200/1000 = 0.2 (20%) r 500 flowering plants 480 red flowers 20 white flowers 320 RR 160 Rr 20 rr

19. Hardy-Weinberg Equilibrium The gene pool of a non-evolving population remains constant over multiple generations; i.e. , the allele frequency does not change over generations of time. The Hardy-Weinberg Equation: 1.0 = p 2 + 2 pq + q 2 where p 2 = frequency of AA genotype; 2 pq = frequency of Aa plus aA genotype; q 2 = frequency of aa genotype

26. *Yes, I realize that this is not really a cheetah.

27. 2) Natural selection As previously stated, differential success in reproduction based on heritable traits results in selected alleles being passed to relatively more offspring (Darwinian inheritance). The only agent that results in adaptation to environment. 3) Gene flow -is genetic exchange due to the migration of fertile individuals or gametes between populations.

29. 4) Mutation Mutation is a change in an organism’s DNA and is represented by changing alleles. Mutations can be transmitted in gametes to offspring, and immediately affect the composition of the gene pool. The original source of variation.

30. Genetic Variation, the Substrate for Natural Selection Genetic (heritable) variation within and between populations: exists both as what we can see ( e.g. , eye color) and what we cannot see ( e.g. , blood type). Not all variation is heritable. Environment also can alter an individual’s phenotype [ e.g. , the hydrangea we saw before, and… … Map butterflies (color changes are due to seasonal difference in hormones)].

32. Variation within populations Most variations occur as quantitative characters ( e.g. , height); i.e. , variation along a continuum, usually indicating polygenic inheritance. Few variations are discrete ( e.g. , red vs . white flower color). Polymorphism is the existence of two or more forms of a character, in high frequencies, within a population. Applies only to discrete characters.

33. Variation between populations Geographic variations are differences between gene pools due to differences in environmental factors. Natural selection may contribute to geographic variation. It often occurs when populations are located in different areas, but may also occur in populations with isolated individuals.

34. Geographic variation between isolated populations of house mice. Normally house mice are 2n = 40. However, chromosomes fused in the mice in the example, so that the diploid number has gone down.

35. Cline , a type of geographic variation, is a graded variation in individuals that correspond to gradual changes in the environment. Example: Body size of North American birds tends to increase with increasing latitude. Can you think of a reason for the birds to evolve differently? Example: Height variation in yarrow along an altitudinal gradient. Can you think of a reason for the plants to evolve differently?

37. Mutation and sexual recombination generate genetic variation a. New alleles originate only by mutations (heritable only in gametes; many kinds of mutations; mutations in functional gene products most important). - In stable environments, mutations often result in little or no benefit to an organism, or are often harmful. - Mutations are more beneficial (rare) in changing environments. (Example: HIV resistance to antiviral drugs.) b. Sexual recombination is the source of most genetic differences between individuals in a population. - Vast numbers of recombination possibilities result in varying genetic make-up.

38. Diploidy and balanced polymorphism preserve variation a. Diploidy often hides genetic variation from selection in the form of recessive alleles. Dominant alleles “hide” recessive alleles in heterozygotes. b. Balanced polymorphism is the ability of natural selection to maintain stable frequencies of at least two phenotypes. Heterozygote advantage is one example of a balanced polymorphism, where the heterozygote has greater survival and reproductive success than either homozygote (Example: Sickle cell anemia where heterozygotes are resistant to malaria).

40. Frequency-dependent selection = survival of one phenotype declines if that form becomes too common. (Example: Parasite-Host relationship. Co-evolution occurs, so that if the host becomes resistant, the parasite changes to infect the new host. Over the time, the resistant phenotype declines and a new resistant phenotype emerges.)

43. Neutral variation is genetic variation that results in no competitive advantage to any individual. - Example: human fingerprints.

44. A Closer Look: Natural Selection as the Mechanism of Adaptive Evolution Evolutionary fitness - Not direct competition, but instead the difference in reproductive success that is due to many variables. Natural Selection can be defined in two ways: a. Darwinian fitness - Contribution of an individual to the gene pool, relative to the contributions of other individuals. And,

46. Directional selection

47. Diversifying selection favors extreme over intermediate phenotypes. - Occurs when environmental change favors an extreme phenotype. Stabilizing selection favors intermediate over extreme phenotypes. - Reduces variation and maintains the current average. - Example = human birth weights.

48. Diversifying selection

51. All asexual individuals are female (blue). With sex, offspring = half female/half male. Because males don’t reproduce, the overall output is lower for sexual reproduction.

55. Natural selection does not produce perfect organisms a. Evolution is limited by historical constraints ( e.g. , humans have back problems because our ancestors were 4-legged). b. Adaptations are compromises. (Humans are athletic due to flexible limbs, which often dislocate or suffer torn ligaments.) c. Not all evolution is adaptive. Chance probably plays a huge role in evolution and not all changes are for the best. d. Selection edits existing variations. New alleles cannot arise as needed, but most develop from what already is present.

56. Genes Within Populations Chapter 21

61. Hardy-Weinberg Equilibrium Population of cats n=100 16 white and 84 black bb = white B_ = black Can we figure out the allelic frequencies of individuals BB and Bb?

65. Hardy-Weinberg Equilibrium

69. Genetic Drift - Bottleneck Effect

76. Sickle Cell and Malaria

78. Kinds of Selection

80. Evolution of Coloration in Guppies

82. Evolutionary Change in Spot Number

96. for a population with genotypes: 100 GG 160 Gg 140 gg Genotype frequencies Phenotype frequencies Allele frequencies calculate:

97. for a population with genotypes: 100 GG 160 Gg 140 gg Genotype frequencies Phenotype frequencies Allele frequencies 100/400 = 0.25 GG 160/400 = 0.40 Gg 140/400 = 0.35 gg 260/400 = 0.65 green 140/400 = 0.35 brown 360/800 = 0.45 G 440/800 = 0.55 g calculate: 0.65 260

98. another way to calculate allele frequencies: 100 GG 160 Gg 140 gg Genotype frequencies Allele frequencies 0.25 GG 0.40 Gg 0.35 gg 360/800 = 0.45 G 440/800 = 0.55 g OR [0.25 + (0.40)/2] = 0.45 [0.35 + (0.40)/2] = 0.65 0.25 0.40/2 = 0.20 0.40/2 = 0.20 0.35 G g G g

100. Genetic variation in space and time Frequency of Mdh-1 alleles in snail colonies in two city blocks

101. Changes in frequency of allele F at the Lap locus in prairie vole populations over 20 generations Genetic variation in space and time

103. Why is genetic variation important? variation no variation EXTINCTION!! global warming survival

104. Why is genetic variation important? variation no variation north south north south

105. Why is genetic variation important? variation no variation divergence NO DIVERGENCE!! north south north south

106. Natural selection Resistance to antibacterial soap Generation 1: 1.00 not resistant 0.00 resistant

107. Natural selection Generation 1: 1.00 not resistant 0.00 resistant Resistance to antibacterial soap

108. Natural selection Resistance to antibacterial soap mutation! Generation 1: 1.00 not resistant 0.00 resistant Generation 2: 0.96 not resistant 0.04 resistant

109. Natural selection Resistance to antibacterial soap Generation 1: 1.00 not resistant 0.00 resistant Generation 2: 0.96 not resistant 0.04 resistant Generation 3: 0.76 not resistant 0.24 resistant

110. Natural selection Resistance to antibacterial soap Generation 1: 1.00 not resistant 0.00 resistant Generation 2: 0.96 not resistant 0.04 resistant Generation 3: 0.76 not resistant 0.24 resistant Generation 4: 0.12 not resistant 0.88 resistant

111. Natural selection can cause populations to diverge divergence north south

112. Selection on sickle-cell allele aa – abnormal ß hemoglobin sickle-cell anemia very low fitness intermed. fitness high fitness Selection favors heterozygotes ( Aa ). Both alleles maintained in population ( a at low level). Aa – both ß hemoglobins resistant to malaria AA – normal ß hemoglobin vulnerable to malaria

114. Genetic drift 8 RR 8 rr Before: After: 2 RR 6 rr 0.50 R 0.50 r 0.25 R 0.75 r

117. AA x AA AA aa x aa aa genotype frequencies: AA = 0.8 x 0.8 = 0.64 Aa = 2(0.8 x0.2) = 0.32 aa = 0.2 x 0.2 = 0.04 allele frequencies: A = 0.8 A = 0.2 A A A A A A A A a a AA 0.8 x 0.8 Aa 0.8 x 0.2 aA 0.2 x 0.8 A 0.8 A 0.8 a 0.2 a 0.2 aa 0.2 x 0.2

125. Expected genotypic, phenotypic and allele frequencies in the offspring?