Consider a trait determined by a rare, simple Mendelian, autosomal dominant allele. What is the concordance between identical twins? Between same-sex fraternal twins?
A)identical concordance = 1; fraternal concordance = 0.071
B)identical concordance = 1; fraternal concordance = 0.143
C)identical concordance = 1; fraternal concordance = 0.250
D)identical concordance = 1; fraternal concordance = 0.333
E)identical concordance = 1; fraternal concordance = 0.500

Question

Quizplus · Accepted Answer

For a rare simple Mendelian autosomal dominant allele, the concordance between identical twins is 100% (1) because they share all of their DNA. The concordance between same-sex fraternal twins is 50% (0.5) because they share on average 50% of their DNA, but for a dominant trait the allele only needs to be present in one copy to be expressed. Therefore, the chance of both fraternal twins inheriting the allele and expressing the trait is 0.5 x 0.5 = 0.25 (25%), which gives a concordance rate of 0.25/0.75 = 0.333 or 33.3% (rounded to two decimal places).

Consider a Trait Determined by a Rare, Simple Mendelian, Autosomal