1. CHAPTER 13 How Populations Evolve
Modules – 13.22

2. 13.13 Variation is extensive in most populations
VARIATION AND NATURAL SELECTION
Variation is extensive in most populations
Phenotypic variation may be environmental or genetic in origin
But only genetic changes result in evolutionary adaptation

3. Many populations exhibit polymorphism and geographic variation
Figure 13.13

4. 13.14 Connection: Mutation and sexual recombination generate variation
Parents A1 A1 A2 A3
MEIOSIS A1 A2 A3
Gametes
FERTILIZATION
Offspring, with new combinations of alleles A1 A2 A1 A3
and
Figure 13.14

5. 13.15 Overview: How natural selection affects variation
Natural selection tends to reduce variability in populations
The diploid condition preserves variation by “hiding” recessive alleles
Balanced polymorphism may result from the heterozygote advantage

6. 13.16 Not all genetic variation may be subject to natural selection
Some variations may be neutral, providing no apparent advantage or disadvantage
Example: human fingerprints
Figure 13.16

7. 13.17 Connection: Endangered species often have reduced variation
Low genetic variability may reduce the capacity of endangered species to survive as humans continue to alter the environment
Studies have shown that cheetah populations exhibit extreme genetic uniformity
Thus they may have a reduced capacity to adapt to environmental challenges
Figure 13.17

8. 13.18 The perpetuation of genes defines evolutionary fitness
An individual’s Darwinian fitness is the contribution it makes to the gene pool of the next generation relative to the contribution made by other individuals
Production of fertile offspring is the only score that counts in natural selection

9. 13.19 There are three general outcomes of natural selection
Original population
Frequency of individuals
Phenotypes (fur color)
Original population
Evolved population
Stabilizing selection
Directional selection
Diversifying selection
Figure 13.19

10. 13.20 Sexual selection may produce sexual dimorphism
Sexual selection leads to the evolution of secondary sexual characteristics
These may give individuals an advantage in mating
Figure 13.20A, B

11. 13.21 Natural selection cannot fashion perfect organisms
This is due to:
historical constraints
adaptive compromises
chance events
availability of variations

12. Connection: The evolution of antibiotic resistance in bacteria is a serious public health concern
The excessive use of antibiotics is leading to the evolution of antibiotic-resistant bacteria
Example: Mycobacterium tuberculosis
Figure 13.22