1. Chapter 23 Notes:
Population Genetics

2. DEFINITIONS
POPULATION: a localized group of individuals belonging to the same species
SPECIES: a group of populations whose individuals have the potential to interbreed and produce fertile offspring (viable)
GENE POOL: all alleles at all gene loci in all individuals in a population

3. We all belong to the same gene pool!!!
A population of flamingos
6 different species of flamingo

4. DEFINITIONS
Microevolution = studies how pop’s of organisms change from generation to generation and how new species originate
Macroevolution = studies changes in groups of related species over long periods of geologic time; determines evolutionary relationships among species

5. Causes of Microevolution:
1) Natural Selection
2) Genetic Drift reduces genetic diversity (changes in the gene pool of a small population due to chance)
Examples:
-Bottleneck Effect: results from drastic decrease in population size
-Founder Effect: few individuals in a population colonize a new habitat

6. Bottleneck Effect

8. 3) Gene Flow (migration of fertile individuals between populations)
4) Mutation (introduces new alleles into a population)
5) Nonrandom Mating (individuals choose mates based upon their traits)

9. Ways Natural Selection Acts on a Population:
1) Stabilizing Selection: eliminates individuals with extreme or unusual traits; existing population frequencies of common traits are maintained

10. *Example of Stabilizing Selection in humans:
*human babies most commonly weigh 3-4 kg; babies much smaller or larger have higher infant mortality rates.

11. -insecticide resistance -peppered moth
2) Directional Selection: favors traits at one extreme of a range of traits; common during periods of environmental change
Examples:
-insecticide resistance
-peppered moth
(Industrial Melanism)

12. Peppered Moth (Industrial Melanism) example:
100 years after the first dark moth was discovered in 1848, 90% of moths were dark;
the light variety continued to dominate in unpolluted areas outside of London.

13. 3) Diversifying (a.k.a. Disruptive) Selection: occurs when environment favors extreme or unusual traits while selecting against common traits

14. 4) Sexual Selection: differential mating of males in a population; leads to sexual dimorphisms
-females tend to increase their fitness by increasing the quality of their offspring by choosing superior male mates (and are therefore “choosier” or more selective when finding a mate)

15. Sexual Selection (cont.)
-males increase their fitness by maximizing the quantity of offspring produced
**as a result, in vertebrate species,
the male is typically the
“showier” sex
-colorful plumage
-lion’s mane
-antlers