Colour Genetics

Here comes the science …

The standard way of working out what colour the possible offspring of two Mau parents will be is the Punnett Square, a simple graphical way of figuring out how the genes from each parent might combine to produce an offspring.

Since each individual has one pair of each chromosome, they have two copies of each gene (one on each chromosome). The Punnett square observes that the reproductive cells (eggs and sperm) get only half the normal number of chromosomes. Since eggs and sperm each carry only one of each chromosome instead of a pair, they carry only one copy of each gene instead of two. Thus a female who carries two different types (or ‘alleles’) for a particular gene produces some eggs that carry one flavour, and some eggs that carry the other.

The Alleles

In the basic Mau coat colours of Silver, bronze and smoke, inheritance of colour can be explained using two sets of alleles: the ‘Agouti’ alleles (A) and ‘Inhibitor’ alleles (I).

The Agouti allele regulates pigmentation in the hair follicle, resulting in a banded, ticked pattern; presence of the allele is necessary to see the tabby or spotted pattern of a cat’s coat.

The Inhibitor allele is responsible for the inhibition of the deposition of brown colour in the hairs of the cat’s coat.  The only ‘colour’ at work here is brown; ‘silver’ is simply the phenotype resulting from an absence of colour; if you make an analogy with hair colour in humans, ‘grey’ hair isn’t really a colour, it’s an absence of colour, due to the coloured pigments no longer being present in hair.

Mau coat colours can be explained using a Punnett square to depict a dihybrid cross, where we consider the Agouti and Inhibitor alleles:

Gene 1: Agouti allele; A-dominant, a-recessive
Gene 2: Inhibitor allele; I-dominant, i-recessive