Mink rats seemed fairly uncomplicated until around 2000, when mink rats were imported to the UK from American lines. When these newcomers were mated with the existing minks, it became apparent we had two completely separate but similar looking genes in play. These are generally known as mink (or English mink), and American mink (or mock mink).
The pearl gene appears to create a longer pale/white undercoat, pushing the pigment closer to the tips of the fur. This gene only has an effect on mink based rats (of either type).
Mink is at the m (mink) locus. The alleles of this locus are:
- M – Dominant wild type (so “no effect”), the rat has normal pigment.
- m – Recessive mink. The black pigment is diluted to a brown or grey colour, sometimes with a slight white or pale undercoat. Yellow pigment is slightly diluted.
American mink has not been officially allocated a symbol, but for use in the fancy I use the am (American mink) locus. The alleles here are:
- Am – Dominant wild type (so “no effect”), the rat has normal pigment.
- am – Recessive American mink. The black pigment is diluted to a brown colour. Yellow pigment is slightly duller.
Pearl is at the Pe (pearl) locus. The alleles of this locus are:
- pe – Recessive wild type (so “no effect”), the rat has normal pigment.
- Pe – Lethal dominant pearl gene. A rat inheriting two copies of this allele will never be born. Mink based rats with one copy of this gene will have a longer pale undercoat, with more pigmentation nearer the tips of the fur.
The phrase “lethal dominant” can be worrisome, but all it means is that rats with two copies of the pearl allele are not viable, and so never born. It does not mean that there is anything wrong with pearl rats, and no issue with kittens suffering.
aamm or aaamam: mink
A-mm: cinnamon
A-amam: cinnamon
aammPepe or aaamamPepe: Pearl
A-mmPepe or A-amamPepe: cinnamon pearl