Example: Inheritance of sickle cell hemoglobin in West Africa, where the sickle cell trait offers survival benefit because of the prevalence of malaria.
|
Genotype
|
Fitness
|
|
Heterozygote
|
1
|
|
Homozygote Allele 1
|
1 – s
|
|
Homozygote Allele 2
|
1 - t
|
where:
• "s" and "t" are the relative benefit of being heterozygous vs each homozygote state. Each is a decimal fraction from 0 to 1. Both "s" and "t" must be positive numbers.
• A value for "s" or "t" of 1 indicates a lethal condition with death prior to reproduction.
frequency of allele 1 at equilibrium =
= t / (s + t)
frequency of allele 2 at equilibrium =
= s / (s + t)
Using the Hardy-Weinberg equation:
frequency of heterozygote state =
= 2 * (frequency of allele 1) * (frequency of allele 2)
frequency of homozygote allele 1 state =
= ((frequency of allele 1) ^ 2)
frequency of homozygote allele 2 state =
= ((frequency of allele 2) ^ 2)
