Cat hair coat colors, patterns and texture are determined by the combined action of several genes. One gene – fibroblast growth factor5 (FGF5) – determines hair length. Short hair is a dominant trait determined by the wild-type form of FGF5. Long hair is a recessive trait. Four mutations in FGF5 have been identified that are associated with long hair in cats. Long-haired cats can carry two copies of the same mutation (homozygote recessive) or have two different mutations, one on each chromosome (compound heterozygote). Three of the mutations are fairly breed specific, while the fourth is present in all long-haired cat breeds and crossbreds, as follows:
Mutation 1 (M1): present in Ragdolls
Mutation 2 (M2): present in Norwegian Forest Cats
Mutation 3 (M3): present in Maine Coons and Ragdolls
Mutation 4 (M4): present in all breeds of long hair cats, including Ragdolls, Maine Coons, and Norwegian Forest Cats.
The Veterinary Genetics Lab offers a test for long hair that detects the 4 common mutations in cats. It is possible that other mutations causing long hair may exist which have not yet been identified. An example of the DNA test report is given below:
Results reported as:
N/N: Cat has short hair. None of the 4 long hair mutations detected. Cat cannot produce long-haired kittens.
N/M1, N/M2, N/M3 or N/M4: Cat has short hair and carries one copy of a long hair mutation. Cat can produce short and long-haired kittens depending on genotype of the mate.
M1/M1, M2/M2, M3/M3 or M4/M4: Cat has long hair and will produce only long-haired kittens when bred to a long-haired mate.
M1/M2, M1/M3, M1/M4, M2/M3, M2/M4, M3/M4: Cat has long hair and carries two different long hair mutations (compound heterozygote). Cat will produce only long-haired kittens when bred to other long-haired cats.
Drogemuller C., S. Rufenacht, B. Wichert, T. Leeb. Mutations within the FGF5 gene are associated with hair length in cats. Animal Genetics 38(3):218-221 (2007).
Kehler J. S., V. A. David, A. A. Schaffer, K. Bajema, E. Eizirik, D. K. Ryugo, S. S. Hannah, S. J. O'Brien, M. Menotti-Raymond. Four independent mutations in the feline fibroblast growth factor 5 gene determine the long-haired phenotype in domestic cats. Journal of Heredity 98(6):555-566 (2007).