Segregation distortion within the equine MHC; analogy to a mouse T/t-complex trait.

Segregation distortion was found for a haplotype of the equine lymphocyte antigen (ELA) system in an extended family of American Standardbred horses. In one sire family, consisting of a stallion and his 17 sons and grandsons, the gene for ELA-A10 (A10) was transmitted to 57.7% of 638 offspring scored (P = 0.001). Significant segregation distortion was not seen for mares or for unrelated stallions, regardless of the ELA markers they possessed. Since the effect was seen for this one sire family and not seen for other stallions with A10, it is unlikely that the gene for A10 is the cause of this phenomenon, but rather A10 is linked to another major histocompatibility complex (MHC) gene causing this trait. This trait appeared analogous to the segregation distortion observed for the T/t complex of the mouse. Since segregation distortion involving MHC genes has been seen in other species, genes for this trait may be a general feature of the MHC.