The DQA1 and DQB1 genes are extremely close to each other on chromosome 6. For this reason, there has been little recombination between these genes. This is commonly observed in the HLA region and is known as ‘linkage disequillibrium’. Therefore, when you genotype an individual and identify their 2 DQB1 and 2 DQA1 alleles, you can almost always determine which DQB1 and DQA1 alleles are on the same chromosome. This combination of DQB1 and DQA1 alleles are known as DQ haplotypes.