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

Explanation

Thalassemia is an autosomal recessive disorder, meaning an affected child must inherit two recessive alleles (tt), one from each parent. If both parents are carriers (Tt), they have a 25% chance of producing a child with two recessive alleles (tt) and thus affected by thalassemia. The Punnett square for Tt x Tt yields the genotypic ratio: 1 TT : 2 Tt : 1 tt, where only the tt genotype results in an affected child. Therefore, the chance of an affected child is 25%. Option A is correct. Other options provide incorrect probabilities for carriers or unaffected children.