GENETIC-CONTROL OF LYMPHOCYTE ANTIGENS IN SHEEP - OLA COMPLEX AND 2 MINOR LOCI

Lymphocytotoxic reagents allowed us to define 11 lymphocyte factors in sheep. After a genetic control of monospecificity had been made, a genetic study based on 400 crossings indicated that nine factors are transmitted in two haplotypes containing 0.1 or 2 factors. The linked factors of the bifactorial haplotypes are the products of two genes at two closely linked loci, OLA- A and OLA- B, having a recombination rate of about 0.6%. The nine factors are the products of five OLA- A and four OLA- B alleles. Allelic frequencies at the two loci, ranging from 0.05 to 0.23 were obtained by two methods. A linkage disequilibrium between the loci is described. Among the possible causes of this, inbreeding is excluded, whereas selective pressure or more probably old fusions between sheep populations must be retained. A tenth factor (frequency 0.33 to 0.35) has a 26% recombination with OLA factors; its locus (OL-X) would be on the same chromosome but very far from the OLA complex. An 11th factor (frequency 0.30) is probably independent of OLA; its locus (OL-Z) may be on another chromosome. The two linked OLA loci give evidence of a major histocompatibility complex in sheep; the observed linkage disequilibrium allows one to foretell certain applications in phylogeny and perhaps in selection. © 1979 Springer-Verlag New York Inc.