Linkage disequilibrium

In this hypothetical example, the A1 and B1 alleles are more often found on the same chromosome than would be anticipated by chance alone. The same is true for the A2 and B2 alleles. Consequently, there is a deficiency of A1 B2 and A2 B1 haplotypes. This discrepancy between the observed and expected haplotype frequencies is linkage disequilibrium.