What can be inferred about a genetic disorder that, when it occurs in monozygotic twins, affects one twin 80% of the time and affects both twins only 20% of the time?
A)Expression of homologous genes is influenced by the gender of the parent who contributed them.
B)Nongenetic factors can influence the expression of identical alleles.
C)The mutation occurred in a somatic cell rather than a germ cell.
D)Mutation repair is incompletely penetrant.

Question

Quizplus · Accepted Answer

When twins are monozygotic (identical), they share identical genomes at all loci. If one twin has a disease that is completely due to genetic variants, then the likelihood of the other twin having the same disease is 100%. If environment or nongenetic factors play a role, the likelihood of the second twin having the disease goes down, especially if the role of the environmental influence on the disorder is much stronger than the genetic influence.

What Can Be Inferred About a Genetic Disorder That, When