Question

Out of a pair of monozygotic twins, one develops hare lip and the other does not. This can be an example of the genetic phenomenon of:

• A. Pleiotropy
• B. Incomplete penetrance
• C. Variable expressivity
• D. Incomplete dominance

Answer 1

Answer: (B)

Incomplete penetrance

Pleiotropy is a phenomenon where a single gene controls multiple traits that seems to be unrelated.
Penetrance refers to the proportion of people with a particular genetic change who exhibit signs and symptoms of a genetic disorder. If some people with the mutation do not develop features of the disorder, the condition is said to have incomplete penetrance. As both monozygotic have identical genetic material, only one of them developing harelip is an example of incomplete penetrance.

Variable expressivity describes the phenomenon of differing phenotype among individuals carrying the same genotype.

Incomplete dominance refers to the phenomenon when a dominant allele fails to express itself completely in the heterozygous condition.

So, the correct option is ' Incomplete penetrance'.