Colour genes

Marking genes

Chinchilla

The rat variety called chinchilla is genetically very unlike chinchilla in the mouse. In the mouse the chinchilla colouration is caused by a c-locus mutation, and the white belly either by separate spotting genes or a-locus mutations. In rats, the chinchilla situation is more complicated. The main part of the story is a spotting gene given the locus Cs, for chinchilla spotting:

  • cs – recessive wild type gene, no white spotting.
  • Cs – dominant white spotting gene, the rat has a white underside and often white facial markings (a blaze or headspot). The gene tends to reduce yellow pigment slightly.

The white spotting gene has variously been referred to as husky, American husky, Aurora spotting, dominant blazed, or the high white gene. In the UK we tend to refer to it as chinchilla white spotting, as the gene tends to only be found in chinchilla lines.

In order to make the chinchilla variety, the rat must also have a second gene alongside the white spotting. This second gene is given the locus name of fy, for fading yellow. Alleles at this locus are:

  • Fy – incomplete dominant fading yellow gene. The black pigment is normal but the yellow pigment is reduced to pale yellow or white.
  • fy – wild type non-fading yellow gene. Yellow pigment is unaffected.