Abstract
The chromosomal distribution of alleles for HLA-A,-B,-C, and -DR and the serum complement protein alleles of factor B and C2 and C4 was studied in normal Caucasian families. Eight combinations of HLA-B, DR, BF, C2, C4A, and C4B markers were found to occur in haplotypes at frequencies significantly higher than expected. In these combinations, which were defined as extended major histocompatibility complex haplotypes, HLA-A showed limited variation. A possible mechanism for the maintenance of extended haplotypes are human analogs of murine t mutants which are characterized by crossover suppression and male transmission bias. One human 6p haplotype, HLA-B8, DR3, SCO1, GLO 2, was found to be transmitted from males to 83% of their offspring. The same haplotype with GLO 1 had no transmission bias. It is suggested that this GLO 2-marked chromosome is a human analog of a murine t mutant.