Consider a trait determined entirely by environmental risk factors for which the chance that a random individual is affected is 25%. What is the concordance between identical twins? What is the concordance between same-sex fraternal twins?
A)identical concordance = 1.0; fraternal concordance = 0.167
B)identical concordance = 0.167; fraternal concordance = 0.167
C)identical concordance = 0.167; fraternal concordance = 0.143
D)identical concordance = 0.143; fraternal concordance = 0.143
E)None of the answer options is correct.

Question

Quizplus · Accepted Answer

Since the trait is determined entirely by environmental factors, the concordance between identical twins would be the same as the concordance between any two individuals in the population, which is 25%. For same-sex fraternal twins, the concordance would be expected to be approximately half of the concordance for identical twins, which is 25% * 0.5 = 12.5%. However, fraternal twins share a greater proportion of their genes compared to non-twin siblings, so the concordance for same-sex fraternal twins might be slightly higher than 12.5%, but it will still be lower than the concordance for identical twins. The closest option is D, which has a concordance of 0.143 for both identical and same-sex fraternal twins (rounded to three decimal places).

Consider a Trait Determined Entirely by Environmental Risk Factors for Which