Recombinant mouse strains with crossovers in the I region of the H-2 major histocompatibility complex were examined by restriction fragment analysis for the presence of polymorphic restriction sites within the Eβ and Eα genes. Nine recombinant mouse strains were shown to have crossed over within a 5 kb DNA segment that contains the large intron between the second and third exons of the Eβ gene. These results are in accord with previous studies mapping a recombination hot spot within this gene. Seven recombinant mouse strains between the p and k haplotypes were shown to have crossed over in a 6 kb segment within the Eα gene. These results show the existence of a recombination hot spot within the Eα gene. Comparison of the H-2 haplotypes involved in these two recombination hot spots suggests that a specific DNA sequence in b, s, f, and q haplotypes may act to promote recombination in the Eβ gene and a specific DNA sequence in the p haplotype may act to promote recombination in the Eα gene.
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