Genetic effects on coat colour in cattle: dilution of eumelanin and
phaeomelanin pigments in an F2-Backcross Charolais × Holstein population
Beatriz Gutiérrez-Gil1, Pamela Wiener1 and John L Williams1,2
1Roslin Institute (Edinburgh), Roslin, Midlothian, Scotland, UK Midlothian EH25 9PS, UK
2Current Address: Parco Tecnologico Padano, Via Einstein, Polo Universitario, Lodi 26900, Italy
An open access article from BMC Genetics 2007,
8:56 distributed under the terms of the Creative Commons Attribution License.
In cattle, the gene coding for the melanocortin receptor 1 (MC1R)
is known to be the main regulator of the switch between the two coat
colour pigments: eumelanin (black pigment) and phaeomelanin (red
pigment). Some breeds, such as Charolais and Simmental, exhibit a
lightening of the original pigment over the whole body. The dilution
mutation in Charolais (Dc) is responsible for the white coat
colour of this breed. Using an F2-Backcross Charolais × Holstein
population which includes animals with both pigment backgrounds, we
present a linkage mapping study of the Charolais dilution locus.
A Charolais × Holstein crossbred population was investigated for
genetic effects on coat colour dilution. Three different traits
representing the dilution of the phaeomelanin, eumelanin, and
non-pigment-specific dilution were defined. Highly significant
genome-wide associations were detected on chromosome 5 for the three
traits analysed in the marker interval [ETH10-DIK5248]. The SILV gene
was examined as the strongest positional and functional candidate gene.
A previously reported non-synonymous mutation in exon 1 of this gene, SILV c.64A>G,
was associated with the coat colour dilution phenotype in this resource
population. Although some discrepancies were identified between this
mutation and the dilution phenotype, no convincing recombination events
were found between the SILV c.64A>G mutation and the Dc locus.
Further analysis identified a region on chromosome 28 influencing the
variation in pigment intensity for a given coat colour category.
The present study has identified a region on bovine chromosome 5
that harbours the major locus responsible for the dilution of the
eumelanin and phaeomelanin seen in Charolais crossbred cattle. In this
study, no convincing evidence was found to exclude SILV c.64A>G
as the causative mutation for the Charolais dilution phenotype,
although other genetic effects may influence the coat colour variation
in the population studied. A region on chromosome 28 influences the
intensity of pigment within coat colour categories, and therefore may
include a modifier of the Dc locus. A candidate gene for this effect, LYST, was identified.