Purebred cats are subject to a number of serious health problems that are not generally experienced by non-pedigreed moggies. This is because their genetic base is very tiny and they are very inbred. Some breeds of cat have been created by taking a single tom cat or queen with an unusual physical characteristic that breeds true. The entire Cornish Rex breed can be traced back to a single parent animal with an unusual genetic mutation.
Cat breeders are continually competing to find the 'purest' of the species - the bushiest tails, longest ears, shortest muzzles etc. Because of this, the physical characteristic of a prizewinning showcat have been gradually exaggerated to the extent that some of them look like an entirely different species of animal. This genetic shifting is most obvious in the two oldest and most distinctive breeds of Showcat - the Persian cat and the Siamese cat.