A polydactyly allele shows  60% penetrance and  variable expressivity. What would you expect to observe in a family carrying this allele?

A polydactyly allele shows 60% penetrance and variable expressivity. What would you expect to observe in a family carrying this allele?

60% of carriers show the trait, and among those who show it, severity varies.

100% of carriers show the trait but with 60% maximum severity.

40% of carriers express the trait to the same degree in an identical manner.

100% of carriers show the trait but the severity varies in only 40% of carriers.

Correct option is A

Correct Answer: (a)
Explanation: Penetrance refers to the proportion of individuals carrying a particular allele who actually express the associated phenotype. A penetrance of 60% means only 60% of carriers will display polydactyly. Variable expressivity indicates that among those who do express the trait, the severity or form of the phenotype differs between individuals. Therefore, the correct expectation is that 60% of carriers show the trait with varying severity.
Information Booster
· Penetrance is an all-or-none concept describing whether a trait is expressed.
· Expressivity describes the degree or intensity of phenotypic expression.
· Variable expressivity results in differences in severity among affected individuals.
· Many autosomal dominant disorders show incomplete penetrance.
· Environmental factors and modifier genes can influence expressivity.
Additional Knowledge
Incomplete penetrance can cause a trait to appear to “skip” generations, even though the allele is present. Variable expressivity explains why individuals with the same genotype may exhibit mild to severe forms of the same condition. Polydactyly is a classic example used to illustrate both these genetic concepts in human pedigrees.