Single Choice

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

ANo chance
B0.5
C0.25
Correct Answer
D1

Solution

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

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