Question

A study is undertaken to map the HLA-DQ loci in a population with a high incidence of celiac sprue. High-resolution HLA typing of the DQA1 and DQB1 loci is performed using polymerase chain reaction sequencing. The frequency of the DQA1'0501-DQB1"0201 haplotype, which has been strongly implicated in autoimmunity, is found to be 0.20. However, in the same population, the frequency of the DQA 1 '0501 allele is 0.3 and the frequency of the DQB1'0201 allele is 0.2. Which of the following terms best explains the observed DQA1'0501-DQB1"0201 haplotype frequency in this population?

A. Heteroplasmy
B. Increased penetrance
C. Linkage disequilibrium
D. Pleiotropy
E. Segregation

Answer 1

The observed haplotype frequency in a population with high incidence of celiac sprue is best explained by 'linkage disequilibrium', a non-random association of alleles at different loci that are found together more often than expected by chance.

Step-by-step explanation:

The term that best explains the observed DQA1'0501-DQB1"0201 haplotype frequency in a population with a high incidence of celiac sprue, given the frequency of the DQA1'0501 allele is 0.3 and the frequency of the DQB1'0201 allele is 0.2, is linkage disequilibrium. This is because the frequency of the haplotype is higher than would be expected if the alleles were independently assorted – a condition known as Hardy-Weinberg equilibrium. In linkage disequilibrium, specific combinations of alleles or genetic markers are found together more often than would be expected from a random formation of haplotypes from alleles based on their frequencies.