Question

Jerry is six years old. His sister Hanah has the autosomal recessive condition neuronalceroid lipofuscinosis that affects learning and coordination. Their parents are healthy.Given that Jerry has a normal phenotype and is not affected by the disorder, theprobability that Jerry is a homozygote for the wild type allele of the gene that causes thecondition is

A)1/3.
B)1/8.
C)1/4.
D)2/3.

Answer 1

The probability that Jerry is a homozygote for the wild-type allele is 1/3, based on his parents' carrier status and the autosomal recessive inheritance pattern of his sister's condition.

Step-by-step explanation:

The question is asking for the probability that Jerry, whose sister has an autosomal recessive condition, is a homozygote for the normal, or wild type, allele. Since both parents are healthy but have produced a child with the condition, they are both likely carriers (heterozygous) for the mutated allele. Using a Punnett square to find the probabilities of offspring genotypes with two carrier parents, we can determine that there is a 25% chance they will have a child who is homozygous affected (aa), a 50% chance they will have a carrier child (Aa), and a 25% chance they will have a child who is homozygous for the wild type allele (AA).

Because Jerry is not affected by the disorder, we exclude the homozygous recessive condition (aa). This leaves us with the possibility of Jerry being a carrier or homozygous for the wild-type allele. Using the probabilities of carrier or non-carrier from the Punnett square (3 out of 4 chance of one), the probability that Jerry is a homozygote for the wild-type allele (given that he is unaffected) is 1/3.