AGB 121: Principles of Animal Genetics and Population Genetics (2+1)

GENE FREQUENCY

• Standard usage in population genetics uses the term gene frequency for what is actually allele frequency.
• Gene or allele frequency is the proportion of one allele relative to all alleles at the locus in the population.

• Gene frequency is usually expressed as a proportion or a percentage.
• The frequency of a phenotype in a population depends on the frequency of the allele controlling it.
• Frequently used over genotypic frequencies in calculations because
  • Genotypes break down to alleles when gametes are formed
  • Alleles (not genotypes) are passed on to progeny

• If f(AA), f(Aa), and f(aa) are the frequencies of the three genotypes at a locus with two alleles “A” and “a”

  The frequency of the A-allele

  • f(A) = p

The frequency of the a-allele

• f(a) = q

f(A) + f(a) = p + q = 1

• Calculation from observed number of individuals with each genotype