Question

Given pedigree shows the inheritance of an autosomal recessive gene A/a. What will be the genotypes 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: Inheritance of an autosomal recessive gene A/a.

Suppose ‘A’ is dominant allele and ‘a’ is recessive allele. The parents of the 1st generation (A and B) produce all normal children even though parent B is affected (aa). This means all the children of 1st generation have Aa genotype. One of the children of 1st generation crosses with an affected one (aa) which produces three children with affected one (2). Hence, the genotypes of 1 and 2 parents are aa and Aa. The cross is given below:

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

1 represents Aa (female unaffected) and 2 represents aa (female affected).