Part III. The human A, B and O blood group is based on one locus with three alle
ID: 144853 • Letter: P
Question
Part III. The human A, B and O blood group is based on one locus with three alleles, IA, IB and Io. IA and 1B are both dominant over lo, but IA and 113 are codominant. Thus, the genotypes MA and IATo have the blood group A phenotype, the genotypes IBI and IPIo have the blood group B phenotype, the genotype IAIB has the AB blood group, and the genotype I°Io has the blood group O phenotype. A sample consisting of 1617 Spanish Basques showed 724, 110, 763, and 20 individuals with blood groups A, B, O and AB, respectively. The best estimates of allele frequencies in the Basque sample are 0.2661 for I, 0.0411 for IB, and 0.6928 for I°. What are the expected numbers of the four blood group phenotypes under HWE? Is this population in HWE?Explanation / Answer
The three alleles are Ia , Ib, Io. Let us represent the allele frequencies as a, b and o for ease of calculation.
If the alleles are in Hardy-Weinberg Equilibrium, then a+b+o=1 and a2 +b2 + o2 + 2ab + 2ao+ 2bo = 1
Given, a=0.2661, b=0.0411 and o=0.6928
Expected number of genotype = expected frequency x total numer
Coming to expected no. of phenotypes, no. of individuals with:
Since the expected and observed numbers are not equal, the population is not in Hardy-Weinberg Equilibrium.
Phenotype A B O AB Expected no. 710.7 94.7 768 35.4 Observed no. 724 110 763 20