Genetic Variation (a) (b) Figure 23.2 Nonheritable variation

Ldh-B b allele frequency Cline 1.0 0.8 0.6 Ldh-B b allele frequency 0.4 0.2 Figure 23.4 A cline determined by temperature 46 44 42 40 38 36 34 32 30 Latitude (°N) Maine Cold (6°C) Georgia Warm (21°C)

Genetic Drift Generation 1 Generation 2 Generation 3 CR CR CR CR CW CW CR CR CR CR CR CW CR CW CR CR CR CR CW CW CR CR CR CR CW CW CR CR CR CR CR CW CR CW CR CR CR CR CR CR CR CR CR CW CW CW CR CR Figure 23.8 Genetic drift CR CR CR CR CR CR CR CW CR CW CR CW Generation 1 Generation 2 Generation 3 p (frequency of CR) = 0.7 p = 0.5 p = 1.0 q (frequency of CW ) = 0.3 q = 0.5 q = 0.0

Genetic Drift: The BottleNeck Effect Figure 23.9 The bottleneck effect Original population Bottlenecking event Surviving population

Gene Flow Figure 23.11 Gene flow and human evolution

Natural Selection Original population Frequency of individuals Phenotypes (fur color) Original population Evolved population Figure 23.13 Modes of selection (a) Directional selection (b) Disruptive selection (c) Stabilizing selection

Natural Selection - Adaptive Evolution (a) Color-changing ability in cuttlefish Movable bones Figure 23.14 Examples of adaptations (b) Movable jaw bones in snakes

Sexual Selection Figure 23.15 Sexual dimorphism and sexual selection

Heterozygote Advantage Frequencies of the sickle-cell allele 0–2.5% Figure 23.17 Mapping malaria and the sickle-cell allele 2.5–5.0% 5.0–7.5% Distribution of malaria caused by Plasmodium falciparum (a parasitic unicellular eukaryote) 7.5–10.0% 10.0–12.5% >12.5%

“left-mouthed” individuals Frequency Dependent Selection “Right-mouthed” 1.0 “Left-mouthed” “left-mouthed” individuals Frequency of 0.5 Figure 23.18 Frequency-dependent selection in scale-eating fish (Perissodus microlepis) 1981 ’82 ’83 ’84 ’85 ’86 ’87 ’88 ’89 ’90 Sample year

You should now be able to: Explain why the majority of point mutations are harmless. Explain how sexual recombination generates genetic variability. Define the terms population, species, gene pool, relative fitness, and neutral variation. List the five conditions of Hardy-Weinberg equilibrium.

Apply the Hardy-Weinberg equation to a population genetics problem. Explain why natural selection is the only mechanism that consistently produces adaptive change. Explain the role of population size in genetic drift.

Distinguish among the following sets of terms: directional, disruptive, and stabilizing selection; intrasexual and intersexual selection. List four reasons why natural selection cannot produce perfect organisms.