ANALYSIS OF HLA-A B RECOMBINANT FAMILIES WITH NEW POLYMORPHIC MARKERS/

The MHC in humans is a much studied region of the genome, the genes of which display a high rate of polymorphism and a high rate of linkage disequilibrium. Four families in which intra-class-I recombination has occurred have been analyzed with six polymorphic markers between HLA- A and -B in order to determine the full haplotypes of the whole famili es and to localize the points of crossover. The previously proposed or der of the markers was confirmed by recombination mapping. In one fami ly, the crossover was shown to have occurred in the 20-kb stretch of D NA bounded by the two markers (P3B and P5) between which no evidence o f linkage disequilibrium was found, a region which constitutes of only about 1% of the distance between HLA-A and HLA-B. Although supportive of the suggestion of a hot spot of recombination in this region, base d on the apparent lack of linkage disequilibrium between the markers P 3B and P5, more such families need to be tested in order to confirm or refute this hypothesis.