Question

The snow goose (chen caerulescens) has both a blue and a white morph. inheritance is mendelian: bb and bb individuals are blue, while bb individuals are white. if 23 geese in a population of 142 are white, and 119 are blue, how many of the blue geese would you expect to be carriers of the b allele (i.e., bb heterozygotes)

Answer 1

We solve the problem using the Hardy-Wineberg equation.

Let us start with the homozygous recessive number of white trait,

∴ q² =  $\frac{23}{142}$ = 0.16

We have the frequency for white trait as q = 0.4

Solving for the frequency of blue trait by using the fact that,

p + q = 1

∴ p = 1 - q = 1 - 0.4 = 0.6

Now we can calculate 2pq in p² + 2pq + q², which is the frequency for heterozygous blue trait,

∴ 2pq = 2 x 0.6 x 0.4 = 0.48

And the homozygous blue trait is given by the expression,

∴ p² = 0.6² = 0.36

Hence, the carriers for the trait of blue are, 0.48 + 0.36 = 0.84, or 84% of 142.

∴ 84% of 142 = $\frac{84 \times 142}{100} = 119$

Answer is 119.