The sites of meiotic recombination in the class II region of the mouse
major histocompatibility complex (MHC) are clustered at hotspots. To
search for hotspots in the class m region, we mapped recombinational b
reakpoints of 79 Ab: H2-D recombinants with 11 DNA markers; these incl
uded Tnx, the gene for an extracellular matrix protein, tenascin X, th
e Notch-related lnt3 gene, and a microsatellite marker, D17Mit13, none
of which had previously been mapped precisely. The results gave the g
ene order of -lnt3-Tnx-Cyp21/C4-Bf-Hsp68c-D17Mit13-Tnfa/Tnfb-D. The cr
ossover sites in 40 of the 79 recombinants were confined within the Eb
/Int3:Tnx/Cyp21 interval. The result demonstrated that an unequal dist
ribution of recombination is a general feature of the mouse MHC, sugge
sting the presence of a recombinational hotspot within the Int3:Tnx in
terval.