7a. Albinism is caused by an autosomal recessive allele that interferes with ski

Question

7a. Albinism is caused by an autosomal recessive allele that interferes with skin pigmentation in mammals. Two normally pigmented parents have an albino girl. What is the probability that their next child will be a boy with albinism? Explain your reasoning.

b. Albinism is caused by an autosomal recessive allele that interferes with skin pigmentation in mammals. Two normally pigmented parents have an albino girl. What is the probability that their first male child will be albino? Explain your reasoning.

Then explain why this answer (7b) is different from that of question 7a.

Explanation / Answer

WT allele = A = Dominant
Mutant allele = a = Recessive
Since it is a recessive mutation, only aa individuals exhibit mutant phenotype.

7a.
Parental cross: Aa X Aa
Progeny: AA Aa Aa aa
Only one out of four individuals exhibit mutant phenotype.
The probability of acquiring mutant alleles does not change with the number of kids as each is an independent event.

The probability for the child to be a boy = 1/2
The probability for the child to be affected = 1/4
The probability for a boy child to be affected = 1/2 X 1/4 = 0.125 = 12.5%

7b.
The probability for the child to be a boy = 1/2
The probability for the child to be affected = 1/4
The probability for a boy to be affected = 1/2 X 1/4 = 0.125 = 12.5%
The probability for the first boy to be affected = 1/2 X 1/4 X 1/4 = 0.03125 = 3.125%

The first male child can be affected or unaffected.
The probability for him to be affected is 1/4.

Related Questions

Navigate

• Browse (All)
• Browse 7
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.