A linkage group composed of three coat color genes and three serum protein loci in horses.

The equine coat color genes chestnut (e) and roan (Rn) have been tested for linkage to 15 protein and blood group loci. Data showing close or fairly close linkage to the serum albumin locus (Al) and loose linkage to the serum esterase locus (Es) for both e and Rn are presented. This means that three coat color genes (To, e and Rn) and three serum protein loci (Al, Gc, and Es) are linked in the same linkage group. The gene order can tentatively be written Al, Gc, Rn, To-e-Es. The implications of the results for studies on coat color inheritance in horses are discussed. The possibility of using electrophoretic markers when testing hypotheses of allelism between coat color genes is suggested. The linkage of e and Es in the horse is proposed to be homologous to the loose linkage of the extension locus (e) and a cluster of esterase loci on chromosome 8 in the mouse, and on linkage group IV in the rabbit. Designations for the known autosomal linkage groups in the horse are suggested.