Question

For a sex-linked gene at which there are two alleles, A1 and A2, in a population and for which the frequency of A1 is 0.9 in females and 0.3 in males, what will be the frequency of the A1 allele in the male offspring (sons) after one generation of random mating?

Answer 1

The pattern of transmission of X linked genes is different from the transmission of autosomal genes because males are hemizygous. Males get their X chromosome from their mother and they transmit their X chromosome only to their daughters.
For X linked genes with two alleles, A1 and A2 females have three possible phenotypes. They are A1A1, A1A2 and A2A2.
Since, males are hemizygous. They have only two possible phenotypes. A1Y and A2Y.
Therefore p and q of males can be easily estimated as p= f(A1Y) and q = f(A2Y)
As per Hardy Weinberg equilibrium, allele frequencies in males and females remain same as long as random mating takes place.
Random mating for one generation produces genotype frequencies that can be predicted from allele frequencies.
Allele frequencies in males and females are stable as long as random mating takes place. Due to sex-dependent differences in transmission of X- linked genes, the male frequencies will be the same as the female frequencies in previous generation.