Multifactorial inheritance of white facial markings in the Arabian horse.

The hypothesis was tested that white facial markings in the Arabian horse show multifactorial inheritance. The hypothesis assumes that (1) alleles at different loci acting in a cumulative manner influence the variation in white facial markings, (2) the amount of whiteness is correlated with the number of genes, and (3) interacting nongenetic factors influence the variation. The study was based on computerized data obtained from the Arabian Horse Registry of America, Inc. The facial region was divided into five areas, and each horse was given a score according to the number of areas with a white marking. Twenty-two sire families were analyzed. Each sire family consisted of a sire, his foals, and the dams of those foals. The results of the investigation, including dam-foal and sire-foal regression analyses, were totally compatible with the hypothesis. A heritability study suggested that about two-thirds of the phenotypic variation in white facial markings among Arabian horses is attributable to genetic differences.