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

2. 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)

3. 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

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

5. Gene Flow
Figure Gene flow and human evolution

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

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

8. Sexual Selection
Figure Sexual dimorphism and sexual selection

9. Heterozygote Advantage
Frequencies of the
sickle-cell allele
0–2.5%
Figure 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%

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

11. 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.

12. 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.

13. 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.