Retinitis pigmentosa, a form of blindness in humans, may be caused by a dominant autosomal gene,...

Retinitis pigmentosa, a form of blindness in humans, may be caused by a dominant autosomal gene, R, or a recessive autosomal gene, a. Thus only A_ rr individuals have normal sight. An afflicted man whose parents are both normal marries a woman of genotype AaRr.

(A) What is the genotype of the afflicted man?

(B) What proportion of the children are expected to suffer from this affliction if R and A map to different chromosomes?

Solutions

Expert Solution

Given that, there are two genes which control retinitis pigmentosa. It can be caused by dominant R allele, or recessive "a" allele.

This means only A_rr are unaffected, whereas aaR_ , A_R_ and aarr are affected.

The man is afflicted, and both of his parents were normal, A_rr. This means, the man will definitely inherit r allele from both parents, and thus it would be rr for the second gene. Thus, the only possible genotype of man is aarr. (Since affected ones cannot have dominant A allele, so the ma must be aa for the first gene).

The cross can be shown as :

(Man) aarr × AaRr (female)

Gamete from man : ar

Gametes from female : AR, Ar, aR and ar.

	ar
AR	AaRr (affected, due to R allele)
Ar	Aarr (normal)
aR	aaRr (affected, due to aa genotype)
ar	aarr (affected, due to aa genotype).

Thus, 3/4th children will be affected in this case.

Answer A: Genotype of man will be aarr.

Answer B: Proportion of children expected to suffer : 3/4 th or 75% or 0.75.

(kindly upvote if the answer was helpful).

gladiator answered 1 year ago

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