Cod fish have two forms of hemoglobin determined by alleles

Cod fish have two forms of hemoglobin determined by alleles ‘m’ and ‘r’ at one locus. A sample of cod taken off the Norwegian coast had the following frequencies of the three genotypes:

mm

mr

rr

Total

130

763

1698

2591

A1. What are the allelic frequencies of ‘m’ and ‘r’?

A2. Are these frequencies compatible with the sample having been drawn from a random-breeding population?

Solution

1. The allelic frequency for m, (Freq m) = [130 + 0.5(763)] / 2591 = 0.1974

The allelic frequency for r, (Freq r) = [1698 + 0.5(763) ] / 2591 = 0.8023

2. If drawn from a random-breeding population the genotype would be in Hardy-Weinberg proportions and would be:

F(mm)= p² = 0.1974= 0.0390, F (mr) = 2pq = 2 (0.1974)(0.8026) = 0.3169 and F(rr)= q² = 0.8026 = 0.6442

And the expected number of individuals in each group would be :

Number (mm)= (0.0390)(2591)= 101

Number (mr)= (0.3169)(2591)= 821

Number(rr)= (0.6442)(2591)= 1669

The actual numbers found in each group were 130, 763 and 1698. There are considerably fewer heterozygotes and more homozygotes than would occur with Hardy-Weinberg equilibrium.