Recognition of alternate alleles and mapping of the Qa1 locus.

Cytotoxicity testing of a new antiserum, B10.A anti-A. TIab, indicates that we have identified products of the Qa1b locus. The strain distribution is antithetical to Qa1a except for strain B10.M, which is reactive with both anti-Qa1a and anti-Qa1b sera, and defines a third allele, Qa1d. Two new recombinants that separate Qa1 and TIa have been established and indicate that Qa1 maps telomeric to TIa. In addition, we have found evidence that other loci, also on chromosome 17, modify the level of detectability of Qa1 antigens by cytotoxic testing.