Locus D (Dilution)

The gene responsible for so-called colour dilution is called MLPH (Melanophilin). In cats, deletion 1 bp in MLPH-gene (Ishida et al. 2006) has been proven in association with the dilution. The black colour is diluted to grey (among the breeders the term "blue colour" is used). Some cat breeds are fixed for this dilute colour, such as Cartesian, Russian Blue, Korat and Chartreux. These cats carry d/d-genotype of D-locus (Dilution). The phenotypic expression of colour dilution is inherited autosomal recessively and the colour dilution comes to expression only in individuals with d/d-genotype. The original wild type D-allele (non-dilute allele) is an allele without deletion mutation; it occurs, for example, in Egyptian Mau and Singapura.

The presence of b/b-genotype in conjunction with d/d-genotype results in a lilac colour. The lilac colour is most common in the British cat breeds:

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The O-locus has been described that is responsible for the red or orange colour: the inheritance of dispositions of O-locus is X-linked (inheritance linked to female X-chromosome). Genomia laboratory does not perform tests for the presence of O-locus. In the presence of at least one O-allele (orange) in conjunction with d/d-genotype the rich red colour dilutes to light cream colour:

Genotypes:

• d/d - an individual shows colour dilution
• D/d - carrier of colour dilution without phenotypic expression
• D/D - full colour without dilution

Example of crossbreds:

By crossing Dd x Dd parents (two carriers of d-allele - dilution), the following offsprings are produced:

• 50% carriers of d-allele - D/d-genotype
• 25% diluted coloration - d/d-genotype
• 25% full colour (undiluted) - D/D-genotype

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References:

Ishida, Y., V. A. David, E. Eizirik, A. A. Schäffer, B. A. Neelam et al., 2006 A homozygous single-base deletion in MLPH causes the dilute coat color phenotype in the domestic cat. Genomics 88: 698-705.