Albinism, lack of pigmentation in humans, is an autosomal recessive disorder. A

Question

Albinism, lack of pigmentation in humans, is an autosomal recessive disorder. A normally pigmented woman who has an albino uncle wishes to marry a phenotypically normal man whose sister is an albino. (Assume that these are the only individuals known to be albino in the two families) What is the probability that the couple's first child is an albino? Unless there is evidence to the contrary, all individuals marrying into the family are assumed to be homozygous. 1/6 1/9 rect Answer 1/18 1/36 ou none of these choices 1/1pts Question 39 The following pedigree shows the inheritance of black hair in guinea pigs.

Explanation / Answer

Albinism is due to an autosomal gene and is expressed in homozygous condition. As such, the problem shall be solved on Mendel’s principles of Dominance and Segregation.

Since both man and woman now have normal pigmentation but one of their close relatives was albino, the genotype of the two individuals shall be heterozygous “Aa” (if we denote albinism with “a” and normal pigmentation with “A”).The chance of having the child albino is-

Aa x Aa

25 % or 1/4 is the probability that their first child will be albino.

Also if both the parents are normal looking and if they have AA genotypes-

0% PROBABILITY OF HAVING AN ALBINO CHILD.

Now if one parent is normal looking but is a carrier then he or she will be heterozygous i.e Aa and if other is perfectly normal then he or she will have AA genotype.

AA X Aa

50% will be normal and 50% will be the carrier.

Thus the probability of having an albino child is only 25% only when both the parents are the carrier.

A a A AA Aa a Aa aa

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