1. Ch 16 Evolution of Populations

2. 16-2 Evolution as Genetic Change
Population Genetics
Hardy-Weinberg Principle: When allele frequencies remain constant, a population is in genetic equilibrium.
p² + 2pq + q² = 1

3. 16-2 Evolution as Genetic Change
Hardy-Weinberg allows us to determine equilibrium frequencies of each genotype in a population.
p² + 2pq + q² = 1 or
AA + 2Aa + aa = 1
q² = 0.33
q = 0.57
p = 1 – q = 0.43
What is the frequency of the heterozygote (Aa)?

4. 16-2 Evolution as Genetic Change

5. Genetic Drift Change in allele frequencies due to chance.
More pronounced in smaller populations where the chance of losing an allele is greater.

6. Founder Effect
Small sample of a population settles in a location separated from the rest of the population.
Alleles that were uncommon in the original population may be common in the new population.

7. Bottleneck
When a population declines to very low number and then rebounds.

8. Gene Flow Increases genetic variation within a population.
Reduces differences between populations.

9. Nonrandom Mating
Promotes inbreeding and could lead to a favoring of homozygous individuals.

10. Natural Selection
Selects individuals best adapted for survival and reproduction.

11. Stabilizing Selection
Eliminates extreme expression of a trait when average expression leads to higher fitness.

12. Directional Selection
Makes an organism more fit.

13. Disruptive Selection
Splits a population into two groups.

14. 16-3 The Process of Speciation
Sexual selection- Operates in populations where males and females differ significantly in appearance.
Qualities of sexual attractiveness appear to be opposite of qualities that might enhance survival.
What do YOU look for in a mate?

15. Prezygotic Isolation
Prevents reproduction by making fertilization unlikely.
Prevents genotypes from entering a population’s gene pool through geographic, ecological, behavioral, or other differences.
Western Meadowlark

16. Postzygotic Isolation
Fertilization occurs but hybrid offspring can’t develop or reproduce.

17. Allopatric Speciation
Physical barrier separates a population into two or more populations.

18. Sympatric Speciation
Species evolve into new species without physical barrier.
Both species live side by side during speciation.

19. Adaptive Radiation
Can occur quickly when a species gives rise to many different species in response to a new habitat or ecological opportunity.
Follows large-scale extinction events.

20. Coevolution
Evolution of one species affects evolution of a closely related species.
Mutualism
Coevolutionary arms race.

21. Convergent Evolution
Unrelated species in different parts of the world evolve similar traits.