Tobiano spotting pattern in horses: linkage of To with AlA and linkage disequilibrium

In a study of 2,786 tobiano and non-tobiano horses involved in paint horse breeding programs throughout the United States, the inheritance of the tobiano color pattern gene was tracked in pedigrees using the tightly linked polymorphic albumin gene. The dominant tobiano allele (T(o)), which produces the tobiano spotting pattern in horses, was in coupling with both AIA and AIB alleles at the albumin locus. The frequency of the T(o):AIA linkage phase among all the homozygous tobiano horses in this study including offspring and parents (N = 127), was 0.08. The T(o):AIB linkage phase was the most frequent (0.92). Linkage disequilibrium exists between the tobiano and albumin loci. The linkage disequilibrium parameter (D) was calculated as D = 0.056 at 79% of maximum linkage disequilibrium.