Australian Rat Genes

The agouti gene

 photo showing a ticked or agouti based pet rat coat
Close up of a ticked/agouti based coat

This is a dominant gene. The letter used to express the agouti gene is A or a.

When the dominant gene A is present, (whether it be Aa or AA), the hairs will be banded with two colours on the same strand. If two copies of the recessive agouti gene (aa) are present, the hair colour will be solid. This is also referred to as non-agouti.

The mink gene

photo showing a mink based pet rat coat
A mink based rat

This is a recessive gene. The letter used to express the mink gene is M or m.

If two copies of the recessive mink gene (mm) are present, the colour of the coat is diluted. When M is present, (whether it be Mm or MM) there is no effect. The mink gene causes a temporary lighter coloured ‘cap’ on the head of juvenile ratlets, which occurs at approximately six weeks of age when the baby coat moults out and is replaced by the adult coat.

The ruby eye gene

photo showing a ruby eyed rat
A ruby eyed rat

This is a recessive gene. The letter used to express the ruby eye gene is R or r.

When the dominant gene R is present (whether it be Rr or RR), there is no effect. If two copies of the recessive ruby eyed gene are present (rr), the eye colour is diluted to ruby (a dark red that can sometimes be mistaken for black) and the colour of the coat is diluted.

The pink eye gene

photo showing a pink eyed rat
A pink eyed rat

This is a recessive gene. The letter used to express the pink eye gene is P or p.

When the dominant P is present (whether it be Pp or PP), there is no effect. If two copies of the recessive gene is present (pp), the eye colour is diluted to pink and the colour of the coat is diluted.

The blue gene

photo showing a blue rat
A blue based rat

This is a recessive gene. The letter used to express the blue gene is D or d.

When the dominant D is present (whether it be Dd or DD), there is no effect. If two copies of the recessive gene is present (dd), the coat will be diluted to blue.

The albino gene

albino double rex pet rat nibbles fingers
An albino rat

This is a recessive gene. The letter used to express the albino gene is C or c.

When the dominant C is present (whether it be Cc or CC), there is no effect. If two copies of the recessive gene is present (cc), the effect is a white coat with pink eyes. This gene is a masking gene, in that it masks all other genes. An albino can carry any of the above genes in any combination, but there is no way to tell visually what genes they might be.

The BEW gene

albino double rex pet rat nibbles fingers
A black eyed white rat

The BEW gene appears to breed as co-dominant. The heterozygotes often have a face marking, ranging from a headspot to a lightning blaze and a chin strap which would suggest that the BEW gene is co-dominant. This isn’t always the case, however, as heterozygotes may have no additional white on them.

Although Black Eyed Whites appear to always be Self (HH) in marking, the fact that two hoodeds can produce them (hooded (hh) x hooded (hh)= 100% hoodeds in all other scenarios and would not be able to produce a self), the BEW gene therefore may cause an overmarking of white. Therefore although the rat may be genetically a hooded (hh) or a berkshire (Hh), the overmarking of white covers up the coloured parts, making the rat appear self. BEW’s often have smudges of colour on them, and very occasionally have patches of colour on them.