For a trait that is completely genetic, what would the concordance be for monozygotic twins?

For a trait that is completely genetic, what would the concordance be for monozygotic twins?

• A. 100%
• B. 50%
• C. 0%
• D. 25%

Answer: (A)

Concordance in twin studies is the probability that one twin has a trait given that the other twin has it. For identical twins who share all their genes, a trait that is completely genetic would be expressed in both twins, so the concordance is 100%. The idea is that if a trait is entirely determined by genetics, there’s no different environmental or developmental influence to cause one twin to express it and the other not. In contrast, traits with only partial genetic influence would show lower concordance in identical twins, and traits with no genetic influence would show little to no concordance. So 100% is the best answer.

Concordance in twin studies is the probability that one twin has a trait given that the other twin has it. For identical twins who share all their genes, a trait that is completely genetic would be expressed in both twins, so the concordance is 100%. The idea is that if a trait is entirely determined by genetics, there’s no different environmental or developmental influence to cause one twin to express it and the other not. In contrast, traits with only partial genetic influence would show lower concordance in identical twins, and traits with no genetic influence would show little to no concordance. So 100% is the best answer.