According to a well-respected study the most inbred cat breeds are Burmese, Havana Brown, Singapura and Sokoke. These cat breeds have the lowest heterozygosity values and the highest coefficient of inbreeding (COI) values. At the second-tier level in terms of the most inbred cat breeds, the study found that the Birman, Abyssinian, Russian blue, Siamese, Egyptian Mau, Turkish Van, Persian and Exotic Shorthair ranked as more inbred than others. There are about 104 cat breeds as a near maximum. The CFA recognises 44 of them.
Heterozygosity and Coefficient of Inbreeding COI
High heterozygosity means a high level of genetic variability whereas low heterozygosity means less genetic variability and higher levels of inbreeding. As I understand understand it, the coefficient of inbreeding is a scale which measures the degree of biological relationship between two individuals. In other words how related two cats of a breed are to one another. The quote below is instructive. I understand that the Bengal cat has only a few founding cats which means all the Bengal cats come from just a handful of parents.
The Bengal’s degree of inbreeding is not referred to in this article as it is not included in the study referred to. My impression based on the prevalence of congenital diseases in purebred cats was that the Siamese and Persian were two of the most inbred cat breeds. The study bears this out. The Bengal has HCM (heart disease) issues and Bengal nose (crusty nose leather).
Inbreeding not only ‘fixes’ type (the cat’s appearance) but also fixes immunodeficiency by which I mean compromise the cat’s immune system making the cat more vulnerable to illness leading to a shorter lifespan.
“In a majority of breeds is now impossible to find to cat unrelated to each other because every pedigree is based on a few early founding cats.” – Joan Miller, Vice President, the Winn Feline Foundation
and cat show judge (1998).
Least inbred cat breed
The least inbred cat breed is the Siberian cat which has the highest heterozygosity value of the cat breeds and which is similar to that of random bred cats. Another cat with a high level of heterozygosity and a low inbreeding coefficient is the Norwegian Forest cat. Click this link to see articles on the Siberian cat.
Wild cats – a small species of wild cat of which the N. African species is the ancestor of the domestic cat
The chart above also shows us that the European wildcat is highly inbred and has a low-level of heterozygosity. According to this chart it is far more inbred than any of the cat breeds. The Southern African wildcat is less inbred than its European counterpart but also more inbred (specifically has a higher coefficient of inbreeding) than any of the cat breeds. While speaking about the wild cats, the Scottish wildcat would also be inbred but for the fact that it is believed to have extensively crossbred with domestic and feral cats which has diluted the cat’s pedigree making it less inbred but no longer purebred. The Scottish wildcats are wildcat hybrids.
The study referred to is: The Ascent of Cat Breeds: Genetic Evaluations of Breeds and Worldwide Random Bred Populations by Monika J. Lipinski and colleagues [LINK].