The molecular organization of the H-2K region of two t-haplotypes: implications for the evolution of genetic diversity.

The genetic diversity between the t12 and tw5 haplotype chromosomes was studied by analyzing the molecular organization of the H-2K region. Twenty-one cosmid clones spanning over 150 kb of the H-2K region of both t-haplotypes were defined, and high resolution restriction maps were determined. Detailed comparison of the t12 and tw5 restriction maps revealed the following. (i) The H-2K regions of both t-haplotypes retain a very similar molecular organization to that reported for B10, BALB/c and AKR. The nucleotide sequence diversity estimated from restriction site polymorphism is 0.68% between the t12 and tw5 haplotypes; these two t-haplotypes are no more similar to one another than BALB/c is to AKR. (ii) Genetic recombination is strongly implicated in generating H-2 polymorphism. (iii) Genetic polymorphisms, defined as small restriction fragment size differences, are observed at multiple sites along the H-2K region. An Alu-like B2 sequence and BAM5-R homologous sequence were identified as the inserted/deleted DNA segments of two of these sites, suggesting that insertion/deletion of mobile elements is a general mechanism for generating genetic diversity.