The MN blood group system is codominant and has three genotypes: NN, MM, and MN.

ID: 55602 • Letter: T

Question

The MN blood group system is codominant and has three genotypes: NN, MM, and MN. In a population of 4250 people, 16% had blood type N. A disease was introduced to the population after an escaped research monkey bit one of the village inhabitants. This disease killed all of the individuals with blood type M, and while those that had blood type N all survived, the treatment for the disease killed them all. After several weeks, life returned to normal in the village. What genotype and phenotype frequencies would be expected as the result of this disease (selection)? What genotype and phenotype frequencies would we expect to find for the MN blood group system in subsequent generations? Assume that Hardy-Weinberg equilibrium was initially in effect Just practice but I can't even figure this one out.

Explanation / Answer

Initial conditions :

Genotype frequency for NN individuals, q2 = 16%

q = 16/100

q = 0.4

we know that p + q = 1

hence p + 0.4 = 1

Allele frequency, p = 0.6

Genotypes

Genotypic frequency

Number of individuals

MM, p2

0.6 * 0.6 = 0.36

0.36 * 4250 = 1530

MN, 2pq

2*0.6*0.4 = 0.48

0.48 * 4250 = 2040

NN, q2

0.4 *0.4 = 0.16

0.16 * 4250 = 680

Total number of individuals in a population, N = 4250

Final conditions :

All individuals with genotype MM died, hence total number of individuals left = 680+ 2040 =2720

Genotype frequency for NN individuals, q2 = 680/2720 = 0.25 = 25 %

Genotype frequency for MN individuals, 2pq = 2040/2720 = 0.75 = 75%

Thus we observe a change in genotype frequencies over the period of time.