The spotted pattern on the Mau is thought to be caused by a spot modifier gene (Sp) that breaks up the coat pattern into discrete areas - i.e spots. This gene is dominant, so heterozygous (Spsp) or homozygous (SpSp) genotypes manifest as a spotted coat [2].
It is often thought that the recessive combination (spsp) will give rise to the striped or 'classic' pattern more typically seen in domestic tabby cats, however other research suggests that another gene (or genes) are involved [1].
The basic coat color gene is black (B), and all Maus are assumed to be homozygous (BB) [2].
The next significant gene is the Agouti signaling gene (A), which does two things - creating alternating colors on the hair shaft (ticking) and lightens the black color on the shaft, allowing the spotted pattern underneath to be revealed. In the case of silver or bronze the dominant gene is present - so homozygous (AA) or heterozygous (Aa) is required.
Finally there is the color inhibitor gene (I), which prevents pigment (primarily) at the base of the hair shaft. So in its dominant form produces a light undercoat. Silver and smoke have this gene dominating - so either homozygous (II) or heterozygous (Ii). Bronze requires the base color showing, so needs recessive homozygous inhibitor (ii) [2] [3].
For Silver both Agouti and Inhibitor must be dominant, the 4 possibilities are:
For Bronze the Agouti must be dominate and the Inhibitor must be suppressed (i.e homozygous recessive), so the 2 possibilities are:
For Smoke, the Agouti gene must be suppressed (i.e homozygous recessive), and the Inhibitor must be dominant, so the 2 possibilities are:
For Black Mau both Agouti and Inhibitor are repressed (i.e. homozygous recessive for both):
The black Mau is not showable (standard recognizes only spotted Mau) [4].
Perhaps the easiest way to recall what genes have what expression (phenotype) is:
Extensive use was made of the following references in the above: