A trait is caused by a rare dominant autosomal allele with full penetrance. Practically all individuals with the trait are heterozygous and result from matings between affected and normal individuals. What would be the expected concordance values for monozygotic and dizygotic twins?
A) 100% for both types of twins
B) 100% for monozygotic twins and 90% for dizygotic twins
C) about 90% for both types of twins
D) 100% for monozygotic twins and 50% for dizygotic twins
E) 75% for monozygotic twins and 25% for dizygotic twins

Question

Quizplus · Accepted Answer

Monozygotic twins share 100% of their genes, so if one twin has the trait, the other will too, resulting in 100% concordance. Dizygotic twins share about 50% of their genes, so the expected concordance is 50% for a dominant trait.

A Trait Is Caused by a Rare Dominant Autosomal Allele