1. Gene Action Fitness Relationship A1A1 A1A2 A2A2 1 + s 1 + s 1
Dominance
A1A1 A1A2 A2A2
1 + s
Recessivity
A1A1 A1A2 A2A2
1 + s t
Overdominance
A1A1 A1A2 A2A2
1 + s t
Underdominance

2. Dominance
Genotype A1A1 A1A2 A2A2
Fitness 1 + s s
S = 0.01 A1

3. Recessive
Genotype A1A1 A1A2 A2A2
Fitness 1 + s
S = 0.01 A1

4. Evolution in lab
populations of
flour beetles
support theoretical
predictions.
Dawson (1970)

5. Overdominance/Heterozygote Superiority
Genotype A1A1 A1A2 A2A2
Fitness 1 + s t
S = t =
Stable equilibrium
is reached A1
Genetic diversity
is maintained

6. Viable allele did not fix in the population
Mukai and Burdick 1958

7. Underdominance
Genotype A1A1 A1A2 A2A2
Fitness 1 + s t
S = t = 0.02
Unstable equilibrium A1
A1 maybe fixed or
lost from the
population

8. Frequency-Dependent Selection
Allele frequencies in a population remain near an equilibrium
because selection favors the rarer allele.
As a result, both alleles are maintained in the population.

9. Frequency-Dependent Selection
Perissodus

10. Incorporating Mutation
Mutation alone is a weak
evolutionary force

11. However, mutation and selection acting in concert
are a powerful evolutionary force