Question

Work out a cross to explain how normal parents may have a sickle-cell anaemic child.

Hint:

Sickle-cell anaemia is an autosomal recessive disorder. Carriers are usually asymptomatic but can pass the defective allele to offspring.

Answer 1

Parental genotype: Both parents are carriers (\(Hb^A Hb^S\)). 
Punnett Square: \[ \begin{array}{c|c|c} & Hb^A & Hb^S \\ \hline Hb^A & Hb^A Hb^A & Hb^A Hb^S \\ \hline Hb^S & Hb^A Hb^S & Hb^S Hb^S \\ \end{array} \] Results: 25% normal (\(Hb^A Hb^A\)). 50% carriers (\(Hb^A Hb^S\)). 25% sickle-cell anaemic (\(Hb^S Hb^S\)).