The expression of the colour white in the cat, or, should one say the absence of colour, overrides the genetics of other colours or patterns in the cat. In other words the visual result will be the same whether the individual cat is black, blue, brown, lavender, orange, whether it is tabby, pointed, or smoke and this applies to all breeds. Thus, it is fascinating to compare the occurrence of white in different individuals and to note the range in the quality, placement, effects upon eye colour and more worrisome, on the occurrence of deafness in these white cats. To understand white a little better, here is some simplified information on the origin of white, its mode of transmission and expression as well as its different names.
It is the endogenous virus FERV1 which is responsible for the genetic mutation resulting in the inhibition of colour, perceived as the colour white in the cat, dog, mouse, horse, and even in humans!
A virus? How is that possible?
Viruses, as undesirable as they might be, play a large role in natural evolutionary phenomena and the changes they bring may or may not be beneficial. More specifically, retroviruses have the ability to collect all the elements that they need to replicate from the nuclei of cells they have infected. Thus, to replicate themselves, they take bits of DNA needed from the host and leave behind mutated remnants in which bits of viral DNA have been substituted for bits of regular DNA. These cells, not destroyed by this mutation, in turn reproduce mutated cells.