Hardy – Weinberg Equilibrium Graph
Principle: If p is the frequency of A allele and q is the frequency of a allele then the expected
genotype frequencies under random mating are p2 for the AA homozygotes, q2 for the aa
homozygotes and 2pq for the heterozygotes.
Calculation: If we take 10 random values of p, then we can calculate q from the equation
p + q = 1. Now from the value of p and q we can assess p2, q2 and 2pq. We can plot a
graph where the horizontal axis shows the two allele frequencies p and q and the vertical axis
shows the expected genotype frequencies.
p
q
p2
2pq
q2
0
0.12
0.22
0.32
0.42
0.5
0.62
0.72
0.82
0.92
1
1
0.88
0.78
0.68
0.58
0.5
0.38
0.28
0.18
0.08
0
0
0.01
0.05
0.10
0.18
0.25
0.38
0.52
0.67
0.85
1
0
0.21
0.34
0.44
0.49
0.50
0.47
0.40
0.30
0.15
0
1
0.77
0.61
0.46
0.34
0.25
0.14
0.08
0.03
0.01
0
Table 1 Value of p, q, p2, q2 and 2pq
p2
2pq
q^2
1.2
Genotype Frequency
1
0.8
0.6
0.4
0.2
0
0
0.12
0.22
0.32
0.42
0.5
0.62
0.72
0.82
0.92
1
Gene frequency of A
Figure 1 : Hardy-Weinberg frequencies of genotype AA, Aa and aa in relation to the frequency of the gene A (p)
Interpretation: The graph shows the proportions of the three genotypes at different frequencies
of the gene A; heterozygotes are most frequent when the gene frequency is 0.5.
Kalpesh Jas
Sem – VI
B.Sc. Zoology (Honours)