Cationic trypsinogen is an enzyme made in the pancreas that helps to digest food

Question

Cationic trypsinogen is an enzyme made in the pancreas that helps to digest food. It is encoded for by the PRSS1 gene.

Individuals with a disorder called hereditary pancreatitis have mutations in the PRSS1 gene, which result in inflammation of the pancreas, possibly leading to permanent tissue damage. The disorder is inherited in an autosomal dominant fashion.

QUESTION:

If a man who is heterozygous for a PRSS1 Ala16Val mutation mates with a woman who is homozygous for normal cationic trypsinogen, what is the probability that their offspring will have hereditary pancreatitis?

Explanation / Answer

Since the mutation shows dominant inheritance, the probaility of inheritance is 0.5 or 50%.

The information missing is about the penetrance of the mutant allele. The information in the text gives that the mutation shows 60% penetrance. With this penetrance, the probability of inheritance is 0.5 x 0.6 = 0.3 or 30%.

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