Question

If both parents are carriers for thalassemia, which is an autosomal recessive disorder, what are the chances of pregnancy resulting in an affected child?

• A. No chance
• B. 50%
• C. 25%
• D. 100%

Answer 1

Answer: (C)

25%

Thalassemia-autosomal-linked resessive
AA-Normal
Aa-Carrier
aa-Disease
$Affected=\frac{1}{4}=$25%

An autosomal recessive disorder like thalassemia is caused by abnormalities in both members of a pair of genes. Both parents may carry a single dose of the gene on one chromosome but have a normal gene on the other chromosome, which prevents the appearance of the disease in the carrier parent. A child must get one abnormal gene from each parent in order to be affected by the disease. Parents who are both carriers of an autosomal recessive disorder have a 25% risk of producing an offspring affected by the disease and a 50% risk of producing normal-appearing carriers.