Glucose-6-phosphate dehydrogenase (G6PD) deficiency is inherited as an X-linked recessive gene in humans. A woman whose father suffered from G6PD marries a normal man. What proportion of their sons is expected to have G6PD? Enter your answer as a fraction.

Let us assume that the presence of "g" allele on the X chromosome causes the disease. An X linked recessive disease is passed from an affected male to his daughters. A female with one copy of "g" allele on her X chromosome would serve as carrier for the disease while the female with two copies of "g" alleles would be affected with the disease.

A male with one copy of the "g" allele on his X chromosome would be affected with the disease. This is due to the fact that human males are hemizygous for X linked genes.

Given that the female had the affected father, the genotype of the female would be "X^gX". The genotype of the normal man would be "XY". A cross between carrier female and normal male would give 1/2 affected sons.