Final answer:
The frequency of the NN genotype among 2,000 British citizens, based on the given MN blood group phenotypes, is 0.213.
Step-by-step explanation:
The question asks about the frequency of the NN genotype in a sample of British citizens and their MN blood group phenotypes. Given the data of 2,000 individuals, where 596 show M phenotype, 978 show MN phenotype, and 426 show N phenotype, we can calculate the frequency of the NN genotype. To find this frequency, we look specifically at individuals with the N phenotype because only individuals homozygous for the N allele (NN genotype) will express this phenotype.
The NN genotype frequency is the number of individuals with the N phenotype divided by the total sample size. Therefore, frequency = 426 / 2000 = 0.213.
The correct answer to the question is D, which corresponds to a frequency of 0.213 for the NN genotype among the sampled British citizens.