Allele Frequency Formula
Calculate the frequency of specific alleles in a population from genotype counts.
Essential for population genetics.
The Formula
p = (2 × AA + Aa) / (2 × total individuals)
Allele frequency measures how common a particular allele is within a population. It is calculated by counting alleles across all individuals in the sample.
Variables
| Symbol | Meaning |
|---|---|
| p | Frequency of allele A (dominant) |
| q | Frequency of allele a (recessive), where q = 1 - p |
| AA | Number of homozygous dominant individuals |
| Aa | Number of heterozygous individuals |
| aa | Number of homozygous recessive individuals |
Example 1
In a sample of 200 people: 98 AA, 84 Aa, 18 aa. Find allele frequencies.
Total alleles = 2 × 200 = 400
A alleles = 2(98) + 84 = 196 + 84 = 280
p = 280 / 400 = 0.70
q = 1 - 0.70 = 0.30
Allele A frequency = 0.70, Allele a frequency = 0.30
Example 2
In 50 plants: 10 RR, 25 Rr, 15 rr. Find allele frequencies.
Total alleles = 2 × 50 = 100
R alleles = 2(10) + 25 = 45
p = 45 / 100 = 0.45
R frequency = 0.45, r frequency = 0.55
When to Use It
Use the allele frequency formula when:
- Analyzing genetic diversity within a population
- Setting up Hardy-Weinberg calculations
- Tracking allele frequency changes over generations
- Studying evolutionary pressures on specific traits