How many genes do cats have? Domestic cats have 20,285 genes and 38 chromosomes (sciencedaily.com). Humans have roughly 20,500 genes (geneticdigest.com). The water flea has 31,000 genes (earthsky.org).
Of these only a small number are concerned with the appearance of the cat. For example the difference between a Siamese and a Maine Coon pedigree cat.
Most of the genes concern the functioning of the cat’s physiology (the day-to-day functions of the cat’s body).
A pair of genes is called an ‘allele’ with one gene coming from each parent. The dominant gene of the pair dictates how the gene is ‘expressed’ (shown in the cat’s behaviour or appearance). The other gene of the pair is recessive.
If one parent is black and that gene is dominant and the other parent is grey, the kitten will be black.
Two recessive genes
When two recessive genes are paired they can determine the trait. For example, if two genes for a grey coat are paired the cat will be grey.
The inbreeding of cats can cause the ‘dormant’ recessive gene to show its effect on the cat which can be detrimental to the cat in e.g. ‘inbreeding depression’ (a compromised immune system).
Homozygous and heterozygous
When both genes of an allele are the same the cat is homozygous and when they are different the cat is called heterozygous.
Cat genome was sequenced in 2007
The genome (complete set of genetic material in the cat) was sequenced from a 4-year-old Abyssinian cat whose name was Cinnamon (see photo above). He is or was a shy cat.
Some cat breeds (purebred, pedigree cats) have been developed from genetic mutations. These were random bred cats which were mutations and they were spotted by breeders and turned into cat breeds through selective breeding. Genetic mutations are rare. They occur ‘perhaps in one million offspring’. Most mutations are recessive.
My thanks to Cat Owner’s Home Veterinary Handbook Third Edition for the information regarding alleles and the quote on mutations.