Categories: Pigmentation phene

Mendelian trait/disorder: no

Mode of inheritance: Multifactorial

Disease-related: no

Key variant known: no

Inheritance: Woolf (1989) and (1990) provided evidence supporting multifactorial inheritance of white markings. Rieder et al. (2008) reported "Heritabilities and genetic correlations for [white head and anterior and posterior leg markings] were high (h(2) > 0.5). A strong positive correlation was found between the chestnut allele at the melanocortin-1-receptor gene locus and the extent of white markings. Segregation analysis revealed that our data fit best to a model including a polygenic effect and a biallelic locus with a dominant-recessive mode of inheritance. The recessive allele was found to be the white trait-increasing allele."

Mapping: Rieder et al. (2008) reported "Multilocus linkage disequilibrium analysis allowed the mapping of the putative major locus to a chromosomal region on ECA3q harboring the KIT gene." A GWAS conducted by Haase et al. (2013) on 1,077 Franches-Montagnes horses from Switzerland, each phenotyped using a standard scale for the extent of white markings on head, fore limbs and hind limbs, and each genotyped with the Illumina 50K equine SNP chip, identified seven QTL which together accounted for 54% of the genetic variance in total white markings. The three QTL with largest effect corresponded to the know coat-colour genes MC1R, KIT and MITF, the latter two alone contributing 26% of the genetic variance.

Molecular basis: By examining phylogenetic relationships of MITF and KIT haplotypes, Haase et al. (2013) concluded "that KIT and MITF act in an additive manner and that accumulating mutations at these loci progressively increase the extent of white markings".

Breed: Freiberger (Horse) (VBO_0000965).
Breeds in which the phene has been documented. (If a likely causal variant has been documented for the phene, see the variant table breeds in which the variant has been reported).