Populations evolve because allele frequencies change

1
Populations evolve because allele frequencies
change

• Things that change allele frequencies
• Mutations
• Gene flow
• Random mating
• Genetic drift
• Natural selection

2
Gene Flow

• Migration of fertile individuals or gametes
  between populations
• Reduces differences between populations

3
Genetic Drift
Change in allele frequency due to chance.
Happens in small populations.
4
Bottleneck Effect (Genetic Drift)
5
Preserving Variation

• Why are unfavorable alleles not eliminated from
  population?
• Diploidy
• Heterozygote advantage
• Ex sickle-cell allele and malaria

6
Natural Selection

• Darwinian fitness contribution an individual
  makes to the gene pool of the next generation
  relative to the contributions of others
• Modes of selection
• Directional
• Diversifying
• Stabilizing

7
Modes of Selection
8
Directional Selection
9
Diversifying Selection