Question

For an autosomal recessive trait, if a normal male and an affected female have a daughter with the dominant phenotype, what are the possible genotypes of both parents? If their daughter with the dominant phenotype goes on to have children with a carrier male, what is the probability that they will produce a child that is a female carrier?

Answer 1

Answer:

The possible genotype of the normal male: AA or Aa

The genotype of affected female: "aa"

The probability of having a carrier girl child= 1/4

Explanation:

The given trait is autosomal recessive. Let's assume that the recessive allele "a" is responsible for the trait while the dominant allele "A" gives the dominant phenotype. The genotype of the normal male can be AA or Aa while that of the affected female would be "aa"

Their daughter has dominant phenotype and therefore, would be heterozygous for the trait with "Aa" genotype. A cross between carrier daughter "Aa" and her carrier male "Aa" would give progeny in following ratio= 1/4 AA: 1/2 Aa: 1/4 aa. Therefore, they have 1/2 probability of having a carrier child.

The probability of having a girl child is always 1/2.

So, the total probability of having a carrier girl child would be 1/2 Aa x 1/2 XX = 1/4