White is not a colour, but rather the absence of colour (pigmentation). The Dominant White (W) is a dominant masking gene that overrides all other colour genes. Therefore, a white cat will have a masked underlying coat colour. However, despite the underlying colour, because of the presence of the Dominant White gene, a cat that is homozygous (WW) or heterozygous (Ww) will have a white coat.
In view of the above, we can say that a male white cat (WW) mating with a female non- white cat (ww) will produce white offspring, all with the Dominant White gene along with a non- white gene. All four offspring will be white but with the potential to produce non-white.
If two of the offspring were to mate together, we would end up with three white cats (WW,Ww.Ww) and one non-white cat (ww).
Health Each cat’s genome will determine physical appearance and personality. It will also play a role in the cat’s health. Some genes passed down through generations can make cats susceptible to certain diseases. I will here focus on polycystic kidney disease which is an inherited condition affecting more particularly Persians and related breeds. The gene responsible for PKD is an autosomal dominant gene (i e one parent with the abnormal gene is enough for offspring to inherit the disease).
A cat with the AD-PKD gene will be born with cysts in the kidneys. Over time, these cysts will get bigger, impair renal function and can even cause renal failure. This inherited condition is found in Persians, exotic Shorthairs and other breeds developed from Persian stock. It is worth noting that all carriers of AD-PKD are affected. Moreover, the gene is dominant and will therefore be passed on to offspring even if mating occurs with an unaffected cat. As PKD is an incurable progressive disease, it is imperative to have breeding cats tested for the AD-PKD gene and, if found positive, prevented from breeding. This will be the only way PKD can be eliminated.
References: http://www.dr-addie.com Genetic and Hereditary Conditions in Pedigree and Domestic Cats John Bradshaw, Cat Sense