Question

One way to classify humans is by their blood type. There are over two dozen ways to group blood types. One of them is by the presence of the D antigen on the surface of blood cells. If an individual expresses the D antigen, they are referred to as Rh positive. This is controlled by an autosomal dominant allele. In a given town, 16% of the population is considered Rh negative.
If this town's high school has 2,000 students, how many would you expect to be heterozygous for the D antigen?

• A. 160
• B. 320
• C. 720
• D. 960

Answer 1

The correct option is D 960

Rh positive phenotype of blood is controlled by autosomal dominant allele D. It is given that, 16% of the population is considered to be Rh negative (dd). It means rest 84% of the population is Rh positive (DD or Dd). According to Hardy Weinberg's principle, a${}^2$ (homozygous recessive) + 2ab (heterozygous dominant) + b${}^2$ (homozygous domianant) = 1.

In the given case, a${}^2$ = 0.16. Hence, a = 0.4.

Also, a + b = 1. Hence, b = 1 - 0.4 = 0.6.

Heterozygous population will be 2ab = 2 x 0.04 x 0.06 = 0.48. Out of 1, 0.48 students are heterozygous for the D antigen. Hence, for 2000 students, 960 students will be heterozygous for D antigen.

Thus, the correct answer is '960.'