Genetics of Coat Color in Cats, Emphasizing DNA Studies
A brief review of the genes controlling cat coat colors and patterns. All of this research has been conducted in the labs of others. Our lab studies coat color of ONLY dogs and cattle. Many of the photos here are taken from the web. These are not photos of cats actually DNA tested for the coat color they illustrate, contrary to my dog and cattle webpages. This is not ideal but since I do not do research on cats, its the best I could do.
Homepage Table of Contents
This webpage was mounted on June. 23, 2008 and last updated on October 16, 2012 by Sheila Schmutz. firstname.lastname@example.org
None of the existing books about cat coat color contain DNA studies. All are based on hypothesized alleles at hypothesized loci to fit data obtained from coat colors and patterns of cats from various breeds and litters. Much of their work may be correct, but some of it may be more complicated than they hypothsized.
This is primarily because no gene acts in isolation. All cats have all these genes. In some breeds the alleles are "fixed" which means all cats are homozygous for the same allele. As a rule of thumb, the more coat colors that occur in your breed, the more genes will be needed to explain the genotype and phenotype of your cat. Furthermore there are interactions among the various genes in the pathway so that some colors are not possible unless particular alleles occur at more than one locus (i.e. a chocolate cat must have have two mutant a alleles at ASIP and two of the b mutations at TYRP1 to be brown).
This webpage has been mounted for educational purposes only. I hope that both students and cat owners will find it useful. The focus of this page is the descriptions of the coat color genes that have been identified in cat at the DNA level and the mutations in those genes that lead to specific colors or patterns. The page does not attempt to be comprehensive and discuss hypotheses for genes or loci that might cause all the colors and patterns in cats. There are several other books or websites that do that. It also does not attempt to discuss all the colors of cats.
The first genes studied at the DNA level in cats were MC1R and ASIP.
No mutation has been reported in MC1R or the E locus in domestic cats but some mutations have been found in wild cats, such as jaguars and jaguarundis. In domestic cat, it is presumed that all cats are E+/E+ and based on this gene alone could produce both eumelanin and phaeomelanin.
Black cats are a/a at ASIP. This type of black, which is recessive, also occurs in horses and in some herding breeds of dogs. Some cat books of sites also describe this a/a genotype as responsible for solid or self colored, but this is only true of the eumelanin solid colored cats - black, chocolate and blue.
The wild type of ASIP is presumed to be a mottled coloration, such as tabby stripes, since the domestic cat is thought to have evolved from a wild cat with a mottled appearance. A tabby is shown on the left in the basket. Some wild cats are a reddish color, probably similar to the lion's color or that of an Abyssian cat. The gene and allele that differentiates tabby (banded hairs) from Abyssian (banded hairs) patterns has not yet been identified.
The gene that causes eumelanin pigment to be brown instead of black is TYRP1, just like in dogs and several other mammals. This gene has been called the B locus. In cats there are two different mutations in TYRP1, leading to two shades of brown: chocolate and cinnamon. Cats that are homozygous for a premature stop codon, known as b1, are cinnamon which is a reddish brown. Cats that were homozygous b/b are typically called chocolate. Lyons et al. (2005) found that cats that are b/b1 would be closer in shade to chocolate.
Note that all solid chocolate or cinnamon cats are also a/a at ASIP because they produce only eumelanin pigment. In the cat fancy, solid is sometimes called self.
Just as in dogs, the gene causing black eumelanin pigment to be diluted to blue or grey is MLPH or melanophilin. A cat with this blue phenotype is typically said to be d/d in genotype. A cat with blue coat color is illustrated on the left by this stately Russian Blue. The same mutation was found in 26 cat breeds.
Ishida et al. (2006) suggest that this MLPH mutation causes black cats to be blue and orange cats to be cream. Likewise chocolate brown cats would be pale brown, often called lilac in cats. Cinnamon brown cats that are also d/d would be a very pale shade presumably.
Ihibitor of Melanin
A yet undiscovered gene causes the pigment in cat hairs to be more intense at the tips and pale at the base, changing gradually over the length of the hair. It is suggested that there in inhibition of melanin granules leading to less pigment in such hairs. The dominant allele I causes these shaded hairs. The recessive allele i+ is homozygous in cats with evenly pigmented hairs.
The C locus: Albino, Siamese, Burmese
The gene responsible for white cats with blue eyes - an albino phenotype is tyrosinase. The mutation in this gene is a premature stop codon. Albino cats usually are homozygous for this recessive mutation (i.e. they are c/c). Tyrosinase is an important gene in several pathways and therefore it is not surprising that such cats are usually deaf. The blue-eyed Angora at the left is likely deaf.
The wirehaired white cat on the right, is not an complete albino since one eye is pigmented. Cat fanciers call this "odd-eyed". What gene makes its coat white? This gene is sometimes called the W gene or locus, but has not yet been identified.
The gene responsible for colored points on a pale body has been found to be tyrosinase in most species studied. The assumption is that the mutation causes temperature sensitive expression of pigment on the cooler parts of the body - ears, muzzle, feet, tail tip and a pale color that looks almost white in some cases on the torso. This has typically been known as the Siamese pattern in cats and the allele is known as cs. Cats homozygous for this mutation are have Siamese points. The pigmented points can be virtually any color.
Another mutation in Tyrosinase is responsible for the dark sepia brown color in some Burmese cats and the allele associated with this color is known as cb. Cats homozygous for this mutation are solid dark sepia brown. For non-cat fanciers, what is confusing is that the Burmese breed of cats do not all have this classic Burmese color!
Cats that are compound heterozygotes, meaning one mutation of each type and therefore a genotype of cs/cb have an intermediate phenotype which is a brownish color with darker points visible either subtly or readily. The Tonkinese cat is noted for this pattern. Cats that are cs/cs have pale bodies with points that are markedly darker in color and readily visible.
Cats that are C/C with no tyrosinase mutations are fully colored or pigmented. The pigment expressed depends on genes at other loci.
The gene causing the difference between the makeral and blotched tabby patterns in domestic cats has recently been found to be transmembrane aminopeptidase Q or Taqpep by a collaboration of the research groups of Greg Barsh and Steve O'Brien. The TaM allele causing the mackeral tabby pattern is dominant to the Tab allele causing the blotched tabby pattern. The Taqpep gene acts in the fetal kitten to determine which pattern it will later have when the fur develops. Another gene, the EDN3 gene interacts and is differentially expressed, relative to the Ta alleles.
The cat at the left is a mackeral tabby and the one at the right is a blotched tabby.
A gene that interacts with Tabby is now being called Ticked. Cats with the dominant TiA have a ticked or Abysinnian pattern instead of being tabby. Tabby cats, whether mackerel or blotched, have a genotype of Ti+/Ti+.
Orange, Calico or Tortoishell Patterns
The cat coat color pattern discussed most often in high school biology classes is this gene. It is a gene on the X chromosome. Thus far the identity of the gene is not known. Because all female mammals have an X/X chromosome makeup (or karyotype) and all male mammals are X/Y, males are hemizygous for genes on the X chromosoeme.
The allele causing these patterns is usually called XO when orange is coded and Xob when black or another pattern, such as tabby, results. The orange female above is orange with subtle variegation in its fur. Most orange cats show this banding of hairs or variegation.
Calico cats, such as the one on the left, produce areas of orange and black and also have white spotting. Such calico cats are females that are XO/Xob. Cats that do not have white spotting but a genotype of XO/Xob are tortoiseshell, such as the cat shown below. The cat on the right also has white markings but does not exhibit a calico pattern of distinct orange and distinct black patches. This cat has orange areas and tabby areas in a more intermingled arrangement. In the cat fancy, such as cat is sometimes called a "torbie", which is presumably a combined term from tortoiseshell and tabby.
Since normal males have only a single X chromosome, they can not exhibit calico or tortoiseshell patterns.
White Spotting and Markings
All of the genes causing white spots or markings have not yet been identified in cats. Mittens, at the left, was my mother's last cat and is presumed to be a Domestic Shorthair. Although he has his paws all tucked under, you can guess by his name that he has white paws also. That type of white marking is very common in cats.
The mutation for white gloves in Birman cats only, has been identified in the KIT gene and is tested by VGL-UC Davis based on the research of Gandolfi et al. Such a white gloved Birman is shown at the right.
Links to Other Coat Color Related Sites
for further information contact:
Sheila M. Schmutz, Ph.D., Professor
Department of Animal and Poultry Science
College of Agriculture and Bioresources
University of Saskatchewan
Saskatoon, Canada S7N 5A8