Q.26 A population has 600 individuals, 150 of genotype AA, 300 of genotype Aa and 150 of genotype aa. What is
the frequency of allele A?
1. 0.5
2. 0.4
3. 0.35
4.0.6
Allele A Frequency in Population: 0.5 Calculation
In this population of 600 individuals, allele A frequency is calculated directly from genotype counts using standard population genetics formulas. The correct answer is 1. 0.5.
Step-by-Step Calculation
Total alleles = 600 individuals × 2 = 1200 alleles. A alleles from AA = 150 × 2 = 300; from Aa = 300 × 1 = 300; total A = 600. Frequency p = 600/1200 = 0.5. (Verifies Hardy-Weinberg: p²=0.25, 2pq=0.5, q²=0.25 matching 150:300:150 ratio).
Option Explanations
1. 0.5 (Correct)
Direct count: 600 A alleles / 1200 total alleles = 0.50, or p = √(AA frequency) = √0.25 = 0.5 under equilibrium.
2. 0.4 (Incorrect)
This might approximate recessive aa frequency (150/600=0.25, √0.25=0.5 for q, but p=0.6 misassigned); ignores heterozygote contribution.
3. 0.35 (Incorrect)
Possible averaging error like (0.25 AA + 0.5 Aa)/2 = 0.375 rounded down; overlooks double-counting rule for diploids.
4. 0.6 (Incorrect)
Equals heterozygote frequency (300/600=0.5) mistakenly taken as allele frequency, or q value (aa-derived) confused for p.
