If both parents are carriers for an autosomal recessive trait, what is the probability that the child will be a carrier?

If both parents are carriers for an autosomal recessive trait, what is the probability that the child will be a carrier?

• A. 50%
• B. 25%
• C. 75%
• D. 0%

Answer: (A)

Understanding autosomal recessive inheritance helps here: a child must inherit two copies of the recessive allele to show the trait, while inheriting just one recessive allele makes them a carrier. If both parents are carriers, each parent can pass either the dominant allele or the recessive allele to their offspring. Crossing Aa with Aa yields four equally likely genotype combinations: AA, Aa, Aa, and aa. Among these, two are carriers (Aa), so the probability the child is a carrier is 1 out of 2, or 50%. There’s also a 25% chance the child will be affected (aa) and a 25% chance to be a non-carrier (AA).

Understanding autosomal recessive inheritance helps here: a child must inherit two copies of the recessive allele to show the trait, while inheriting just one recessive allele makes them a carrier. If both parents are carriers, each parent can pass either the dominant allele or the recessive allele to their offspring. Crossing Aa with Aa yields four equally likely genotype combinations: AA, Aa, Aa, and aa. Among these, two are carriers (Aa), so the probability the child is a carrier is 1 out of 2, or 50%. There’s also a 25% chance the child will be affected (aa) and a 25% chance to be a non-carrier (AA).