Several members of the Fitzsimmons family have polydactyly,and they differ in their numbers of extra fingers and toes.Yet,certain relatives who should have extra digits don't,such as Megan Fitzsimmons.She has two children,a son with two extra fingers and a daughter with an extra toe,and her father has an extra digit on each hand and foot.Polydactyly in this family is
A)variably expressive and incompletely penetrant.
B)invariably expressive and completely penetrant.
C)pleiotropic and a phenocopy.
D)dominant and recessive.

Question

Quizplus · Accepted Answer

The fact that some relatives with the polydactyly trait do not express it, such as Megan Fitzsimmons, suggests incomplete penetrance. The fact that different relatives have varying numbers of extra digits suggests variable expressivity. Therefore, the best choice is A, variably expressive and incompletely penetrant.

Several Members of the Fitzsimmons Family Have Polydactyly,and They Differ