Question

Neurofibromatosis is caused by an autosomal dominant allele, N, and is commonly seen in families. The symptoms range from small cafe-au-lait (brownish) spots to larger spots to cutaneous, subcutaneous and plexiform neurofibromas - tumors that are found within the nervous system. Individuals with mild forms of the disease can have just the brownish spots. Individuals with severe forms of the disease can have significant growths and malformations. Every heterozygote (N/+) has some symptom, but only a few percent of individuals have significant growths and malformations. What genetic terms should be used to describe this condition?

A.It is incompletely penetrant and shows full expressivity.

B.It shows full penetrance and expressivity..

C.It is incompletely penetrant and shows variable expressivity.

D.It is fully penetrant and shows variable expressivity..

Answer 1

Complete penetrance means, every individual having the gene will express. Incomplete penetrance is when the trait is not expressed in all individuals even though they have the gene.

Expressivity is variability in the expression of the trait, when an allele is penetrant.

In this case every heterozygous individual has some symptom or the other. Meaning penetrance is complete.

But expressivity is not complete. Because the expression is different in different individual , as some are showing mild symptoms and some show significant growth and malformations.