Question

Given pedigree shows the inheritance of an autosomal recessive gene (A/a). What is the genotype of 1 and 2 parents?

• A. AA, aa
• B. aa, AA
• C. Aa, aa
• D. Aa, Aa

Answer 1

The correct option is C Aa, aa

Given: A/a is an autosomal recessive gene.
Suppose ‘A’ is dominant allele and ‘a’ recessive allele.
2 represents female affected and so her genotype will be aa. Since 2 has genotype aa, her parents will have the recessive allele 'a' in their genotypes. However, her father is affected which means his genotype is aa. Her mother is unaffected but should has 'a' allele and so her genotype will be Aa. Hence, the parents genotype will be Aa and aa. The cross is given below:

$\begin{array}{ccc}& \text{A}& \text{a}\\ \text{a}& \text{Aa}& \text{aa}\\ \text{a}& \text{Aa}& \text{aa}\end{array}$