marfan quest -

[ArchivalUser]

mumbai

ok guys it seems there r different ans for this question ,what i feel is ,incomplete penetrance is right if we consider parents who r normal.
but if we consider sis having normal lens ,we can also tick variable expression.
and offcourse as allready said marfan is classic eg of pleiotrophy

[ArchivalUser]

DOC OJ

one more note however,review of the litt, will show that marfans syndrome does express variable expressivity but NOt
incomplete penetrance.This means another explanation should be found for the so called normal parents.

[ArchivalUser]

di

This is what Kaplan says,
incomplete penetrance is distinguished from variable expression in that the non penetrant gene has NO phenotypic expression at all. The penetrance of a disease causing mutation is quantified by estimating the propotion of obligate carriers who display the disease phenotype.