Question

Glucose-6-phosphate dehydrogenase deficiency (G6PD) is inherited as an X-linked recessive allele in humans. A woman whose father suffered from G6PD marries a man who has the disease.
(a) What proportion of their sons is expected to be G6PD?
(b) If the husband were G6PD deficient would you change your answer in part (a)?
(a) zero; (b) no
(a) 1/2; (b) yes
(a) 2/3; (b) no
(a) 100%; (b) no
(a) 1/2; (b) no

Answer 1

Answer:

(a) 1/2; (b) no

Explanation:

Glucose-6-phosphate dehydrogenase deficiency (G6PD) is an X-linked recessive disorder and the woman's father was diseased so it means that woman is a carrier of the allele but has normal phenotype. It means that she will have XXᵇ genotype.

In contrast to this, her husband is diseased so his genotype will be XᵇY.

The Punnett square diagram related to the cross is attached.

(a) Proportion of their sons expected to be G6PD is 1/2:

They both may give birth to 4 progeny with genotypes XXᵇ, XᵇXᵇ, XY and XᵇY. It means they both may have 2 sons out of which one with genotype XᵇY will be diseased while the one with genotype XY will be healthy. So the proportion of their sons having G6PD is 1/2 or 50%.

(b) If the husband were G6PD deficient, the answer will not change.

The reason behind this is that this disease is caused by an allele located in X chromosome. But father contributes only Y chromosome to his son not X chromosome. The X chromosome will affect the genotype of his daughter not son that is why answer will not change. It means they will still have 1/2 of their sons diseased.