Allele of Cr gene MATP is one of the many alleles responsible for diluting of horse colour. Allele Cr is a semi-dominant gene with the so-called dosing effect. Presence of one allele Cr affects the red pigment and changes the colour to yellow or gold, however, it does not affect the black pigment. Two Cr alleles lighten almost completely the red pigment and have a lightening effect on black pigment. In the presence of two Cr alleles, eyes are lightened to a blue colour.
If a horse has one Cr allele (heterozygote NCr), the so-called first dilution occurs and the base chestnut colour is changed to palomino, bay to buckskin and black to smoky black. In the case, two Cr alleles are present (homozygote CrCr) double dilution occurs and the basic chestnut colour changes to cremello, bay to perlino and black to smoky cream.