Page "Cat coat genetics" Paragraph 44

The genetics involved in producing the ideal tabby, tipped, shaded, or smoke cat is complex.

Not only are there many interacting genes, but genes sometimes do not express themselves fully, or conflict with one another.

For example, the melanin inhibitor gene sometimes does a poor job blocking pigment, resulting in an excessively gray undercoat, or in tarnishing ( yellowish or rusty fur ).

Likewise, poorly-expressed non-agouti or over-expression of melanin inhibitor will cause a pale, washed out black smoke.

Various polygenes ( sets of related genes ), epigenetic factors, or modifier genes, as yet unidentified, are believed to result in different phenotypes of coloration, some deemed more desirable than others by fanciers.