1. Gene flow is the movement of traits between populations.
Mechanism – Migration
Keeps neighboring populations similar.
Low gene flow = increased chance populations evolve into different species.

2. Gene Pool All genes in a population
Relative frequency = number of times an allele occurs in a gene pool

3. A normal distribution graphs as a bell-shaped curve.
most fall in the middle
decreases towards each end
Traits not undergoing natural selection have a normal distribution.

4. Normal Distribution in Humans
Most individuals lie in the middle and fewer individuals can be found at the ends.

5. Directional selection favors phenotypes (physical traits) at one extreme.

6. Directional Selection in Humans
More darker skinned individuals closer to equator.

7. Stabilizing selection favors the intermediate phenotype.
A birthweight of 7-8 lbs. is favored.
Heavier and lighter birthweights are selected against.

8. Male – more masculine favored. Female – more feminine favored.
Disruptive selection favors both extreme phenotypes.
Male – more masculine favored.
Female – more feminine favored.

9. Genetic drift
Random change in allele frequencies that occur in small populations.
Founder effect – migration of individuals from a population

10. Speciation Formation of new species
Reproductive isolation – two populations cannot interbreed and produce fertile offspring

11. Mechanisms Leading to Reproductive Isolation
Behavioral Isolation – differences in courtship rituals
Geographic Isolation – natural barrier
lake or mountain
Temporal Isolation – time differences in breeding

12. Behavioral, geographic or temporal?

13. Behavioral, geographic or temporal?

14. Behavioral, geographic or temporal?