# A man, Penoy, whose sister died in early childhood from a recessive lethal disease marries a woman Esmae, who has the same family history. Because Penoy has survived beyond childhood, he does not have the disease, but he may be a carrier (i.e. heterozygous, as may also be the case with Esmae). What is the probability that their first child will suffer from the disease? [Hint: first calculate the probability that Penoy is heterozygous; then determine the probability that both parents are carriers. Remember that he has survived to adulthood when calculating this probability].

Question

A man, Penoy, whose sister died in early childhood from a recessive lethal disease marries a woman Esmae, who has the same family history. Because Penoy has survived beyond childhood, he does not have the disease, but he may be a carrier (i.e. heterozygous, as may also be the case with Esmae). What is the probability that their first child will suffer from the disease? [Hint: first calculate the probability that Penoy is heterozygous; then determine the probability that both parents are carriers. Remember that he has survived to adulthood when calculating this probability].

Step 1

In the given scenario, as the male survived beyond childhood but is a carrier of the disease, it could be possible that it is an autosomal recessive disease. So, as per the question, there can be two scenarios:

Case 1: The man is the carrier (XaY) and the woman is unaffected (XX). In this case, XaX, XaX, XY, XY are the possible genotypic combinations. So, the female offsprings will be carriers of the disease while the male offsprings will remain unaffected. Hence, the probability of the first child to be affected is 0.

Case...

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