Cationic trypsinogen is an enzyme made in the pancreas that

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.Studies of large human populations have determined that the penetrance of a particular PRSS1 mutation, Arg122His, is 86%. What does this means for individuals with the predisposing genotype?

They have an 86% chance of showing the associated phenotype.

They have an 14% chance of showing the associated phenotype.

They will express 86% of the associated phenotypes.

They will express 14% of the associated phenotypes.

Solution

Answer: a. They have an 86% chance of showing associated phenotype.

We should try to understand the term \'penetrance\' for answering the above question. Penetrance in genetics refers to the proportion/percentage of offspring ( possessing a specific genotype) which displays that particular phenotype corresponding to that/ expected of that particular genotype. For example, If only 70% of offspring of a specific genotype show the expected specific phenotype, then the particular gene is said to be 70% penetrant.

In the above question, the penetrance of a particular PRSS1 mutation, Arg122His, is 86% So we can conclude that individuals with the predisposing genotype have an 86% chance of showing the associated phenotype.

Note: Penetrance is different from expressivity. Penetrance tells us the extent up to which the gene is phenotypically expressed in a population whereas the expressivity corresponds to the degree of expression which varies between individuals. [That is why option c and d are wrong.]