Question

In: Biology

Albinism is a rare autosomal recessive trait in which there is a complete absence of melanin...

Albinism is a rare autosomal recessive trait in which there is a complete absence of melanin pigment in the skin, eyes, and hair. A normally pigmented woman whose parents are normal has a brother who is albino. She marries a normally pigmented man whose grandfather was albino. What is the probability their first child will be albino?

I would like to see the problem worked out. Dont understand why it is 1/12. Thank you in advance

Expert Solution

Albinism is an autosomal recessive trait, let the alleles be A- normal and a- recessive.

Both parents of the woman are phenotypically normal, but they have one affected progeny, this shows both parents are heterozygous, and the woman is phenotypically normal.

Aa * Aa

	A	a
A	AA ( normal)	Aa ( normal)
a	Aa (normal)	aa ( albino)

probability that the woman is a carrier= number of carriers/number of phenotypically normal progenies

= 2/3

Man`s grandfather is affected, grandfather's genotype is aa, let grandmother be normal and her genotype is AA.

aa * AA

Aa

so the man`s one parent is Aa, let the other parent be AA

Aa * AA

	A	a
A	AA ( normal)	Aa ( normal)

Probability that the man is Aa= number of Aa/total number of progenies

=1/2

probability of getting aa progeny for Aa woman and Aa man= probability of getting aa progeny for Aa and Aa=number of aa/total number=1/4

( from first punnet square)

so probability of getting albino progeny for this man and woman= probability that woman is a carrier probability that man is the carrier probability of getting aa progeny for Aa woman and Aa man = 2/31/21/4=1/12

gladiator answered 2 years ago

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