I-Locus

I-Locus controls the intensity of the red pigment in dogs through affecting the expression of the pheomelanin pigment. This means that recessive I-allele is responsible for cream, cream-white or pure white coat colour.

In dogs there are two types of pigment that create coat colour: eumelanin and pheomelanin. While the eumelanin is a dark pigment causing black coat colour, the pheomelanin is a red pigment. I-Locus causes so called »extreme dilution« of the pheomelanin. The mutation onI-Locus does not affect the eumelanin so that the black coat and the black hair ends remain black.

Pure white coat colour in some breeds are a combination of extreme dilution of the pheomelanin (I-Locus) and the absence of eumelanin (E-Locus genotype e/e). Dogs with pure white coat colour are not albino and retain pigmentation in their nose, leather, eye rims, lips, or pads.

Although an i/i genotype at I-Locus cause cream to white coat colour in many dog breeds, it is probable that other modifier alleles exist and explain the cream to white coat colour in some breeds.