1. 23.3 Genetic Drift

2. Genetic Drift
In a population individuals may pass a certain allele on to their offspring more by random chance.
Over time the frequency of an allele becomes less common.

4. Genetic Drift and the Bottleneck effect
A change in an allele frequency that dramatically changes a population. Often occurs in a severe selective pressure, like a disease.

5. Genetic Drift and the Founder effect
When a small population breaks off of another larger population by means of migration or separation; this is called the founder effect.

6. Case study of the Prairie chicken
Page 489.

7. Key Points of Genetic Drift
Genetic drift is significant in small populations.
Genetic Drift can cause allele frequencies to shift at random.
Genetic Drift can lead to a loss of genetic variation within a population.
Genetic Drift can cause harmful alleles to become fixed.

8. Gene Flow
Another important evolutionary force is gene flow, or the flow of alleles in and out of a population resulting from the migration of individuals or gametes.
While some populations are fairly stable, others experience more flux. Many plants, for example, send their seeds far and wide, by wind or in the guts of animals; these seeds may introduce alleles common in the source population to a new population in which they are rare.