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What is the genotype of the only child of the third mating from the left in the third generation?





A. Aa
B. AA
C. A?
D. Aa

This question is part of Pedigree Chart Reading
Asked by Despinoza, Last updated: Mar 28, 2020

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4 Answers

John Adney

John Adney

Answered Jun 29, 2017

No, the answer is Aa.

We know that the father of this child is "aa" because they're affected. The mother is not affected and therefore must be "AA" or "Aa"

If you do "AA (mother) x aa (father)" then all of the offspring will be heterozygous "Aa"

If you do "Aa (mother) x aa (father)" then 50% of the offspring will be affected "aa" and 50% will be heterozygous "Aa".

Since the only child is unaffected, it can't be "aa", and therefore must be heterozygous "Aa"

 

John Adney

John Adney

Answered Jun 09, 2017

This answer is wrong. As the child has 1 affected parent they must have inherited at least one a allele from this parent as the parent has to be homozygous. As the child is unaffected they must also have an A allele or they would be affected. The correct answer should be Aa not A?.
 

John Adney

John Adney

Answered May 01, 2017

Why is it A? I also have a few other questions.
 

John Smith

John Smith

Answered Apr 12, 2017

A?
 

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