October 31, 2012

Genetic Analysis Of Unusually Curly Haired Selkirk Rex Completed

Appearance plays a large part in choosing a mate, whether that is your human spouse or your animal pet. Many human societies place a high value on curly hair for appearance — as generations of perm-offering hair dressers can attest. It should be no surprise that pet owners and breeders are attracted to curly haired animals more frequently.

Three curly-haired varieties have been recognized and developed into competitive breeds already. A new study from the University of Veterinary Medicine, Vienna, describes a fourth curly haired breed, the Selkirk Rex, as genetically distinct from previously known breeds. Published in the Journal of Heredity, the study presents a genetic analysis of this unusual feline.

The history of the breed starts in Montana. A domestic cat rescued from a shelter in 1987 gave birth to a curly haired kitten. This kitten mated with a Persian male and gave birth to a mixed litter of curly and straight haired kittens, strongly suggesting that the mutation for curly hair in the original rescued cat is dominant. The presence of the mutation on one of the two copies of the gene involved is sufficient to cause cats to have curly hair. The curly haired Persian mix kittens were attractive and soon recognized as a new breed: the Selkirk Rex.

Extremely popular, the Selkirk Rex can be found at breeders worldwide. Even with this popularity, there had been no attempt to characterize the mutation responsible for the curly hair. Serina Filler of the University of Veterinary Medicine, along with colleagues from the University of California, Davis and Agrobiogen, has investigated the new breed to present an initial description of the underlying genetic mechanism.

The mutation is dominant, meaning Selkirk Rex cats could be either homozygous — carrying two copies of the mutation - or heterozygous — carrying only one copy of the mutation and one "normal" copy of the gene. Heterozygous Selkirk Rex cats are more popular. They present rounded ears, a more rounded head and a fully curled coat, which all conform to the written standard for the breed. Homozygous cats, on the other hand, tend to lose a large amount of hair when young. They do not show bald areas of skin, however.

Filler and her team investigated the pattern of inheritance for these traits. They examined the DNA for nearly 150 cats and were able to show that the gene mutated in Selkirk Rex is distinct from mutations in other recognized breeds. They named this mutation Selkirk Autosomal Dominant Rex, or SADRE. An analysis of the 20 available pedigrees suggests that the original mutation presented approximately 8 or 9 generations ago, fitting in with the breed's known history.

Cross breeding in cats is very closely controlled. It is permitted to cross Selkirk Rex with a variety of other breeds, including Persians, Exotic Shorthairs, British Shorthairs, and British Longhairs. This crossbreeding makes the Selkirk Rex a genetically diverse breed with a low coefficient of inbreeding. The breed seems to be closely related to both Persian and British Shorthairs, probably reflecting the frequency with which they are crossbred. The British Shorthair influence seems more pronounced and is consistent with the overall body shape of the Selkirk Rex.

The study confirms that the Selkirk Rex breed arose from a single cat with a spontaneous mutation about 25 years ago. The mutation has been comparatively easy to retain because of its dominance.

Filler says, “The present level of diversity within the Selkirk Rex would seem to be sufficient for us to consider limiting the number of other breeds to which the cats may be crossed. This would help it to develop a unique head and body shape and made it even more distinct.”