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 student 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. $538$

Answer 1

Answer: (D)

$538$

16% of the student population is Rh${}^{-}$, that the frequency of the recessive allele (q) is .16

The frequency of the dominant allele is determined by p+q = 1

p + 0.16 = 1

p = 1 - 0.16

= 0.84

According to the Hardy Wienberg equation, the heterozygous condition in the population is represented by 2pq

= 2 (.16 x 0.84)

=0.2688

For a population size of 2000 = 0.2688 x 2000

= 538