Cat coat genetics (part 2)
Please note that you are reading the old version of this article. You can find the updated article here.
In the first part of "Cat coat genetics" article we discussed the genetics of feline coat colors and we explained some of the coat patterns. In the second part we now continue with coat patterns, lengths and textures. Read on to learn more!
COAT PATTERNS - Guide through cat coat patterns and colors
Tortoiseshell and calico or tricolor
Tortoiseshell is a pattern characterized by mottled patches of orange and non-orange, most commonly black (or their diluted forms: cream, ginger, red and blue, tabby, grey). These beauties can also have white spots in their fur. Calico versions, aka tricolor cats, have a significant amount of white in their coat, and the red and black patches are not mottled but form patchwork. Thus, all calico cats are tortoiseshell, but not all tortoiseshell cats are calico.
Tortoiseshell and calico cats are almost exclusively female. The reason for this is because the pattern is a result of a differential X chromosome inactivation, and males carry only one copy of the X chromosome.
Female cats carry two copies of the X chromosomes in their cells. One of these chromosomes will be silenced in all of the cells by a random chance. This means that in some cells one X chromosome will be silenced and in the other cells the other one. It is completely random. As already mentioned, the gene for the orange color (O) lies on the X chromosomes and comes in two variants (alleles) – the orange (O) and the non-orange (o). The orange allele O codes for the orange pigment "phaeomelanin", and the non-orange o for the black/brown pigment "eumelanin". If a female cat is a heterozygote for this gene (Oo), it will carry the orange allele (O) on one X chromosome and the non-orange allele (o) on the other X chromosome. The cells in which the first X chromosome is silenced will express only the non-orange gene, and therefore produce the black (or brown) pigment, and the other cells will produce the orange pigment. This is why some patches on the coat will be orange and some will be black. Additionally, a recessive dense pigmentation gene (D/d) can modify the O gene. It can modify orange to cream, black to grey or blue etc. This is why some tortoiseshell cats are chocolate or blue.
The third color of tortoiseshell is a product of a completely separate gene. If they have the white patches, then these are a result of the white spotting gene, as explained in Part 1 of this blog.
Since the male cats carry only one copy of the X chromosome (and a Y chromosome), there is no X inactivation in their cells. This means that they will possess only one allele of the O/o gene present on their X chromosomes and it will be expressed in all the cells the same. Thus, male cats will either be all orange or completely non-orange. The rare male tortoiseshell accidents are usually a result of either an extra X chromosome (XXY), or they are chimeras.
Colorpointed beauties have darker pigmentation on their faces, ears, feet and tails, and a lighter coloration on the rest of their body. A pointed pattern is a form of partial albinism, due to a mutation in tyrosinase (an enzyme involved in the production of melanin). The mutated version of this enzyme is heat-sensitive, and it fails to work at normal body temperatures. It activates only in cooler areas of the skin (lower than 33 °C). Therefore, &coolest parts of the body will be pigmented darker than the rest, such as extremities and face. These pigmented points can be very dark in color, almost black, or cool grey, light brown or lilac.
Siamese cats are most commonly associated with this coat pattern, but many other domestic cats can also be colorpointed.
There are two ways in which a cat may turn out to be completely white in appearance. In the first scenario, there is a mutation in the tyrosinase gene, and in the second case there is a lack of melanocytes in the skin.
1. The gene coding for the tyrosinase enzyme is the C gene. The dominant allele codes for a fully functional protein and all the carriers will show full coat pigmentation. There are two recessive alleles of this gene that cause two forms of albinism: complete and temperature sensitive. The temperature sensitive albinism (explained above) is expressed in e.g. Burmese, Siamese and Tonkinese breeds. The allele causing the complete albinism results in the appearance of the fully white cat. True albinism is a very rare case though.
2. The disrupted replication and migration of melanocytes into the skin is caused by the dominant allele of the white masking gene. All the cats carrying this allele (W/W and W/w) will appear white, even if they carry other color genes. Only recessive homozygotes (w/w) will express the normal pigmentation. These cats are at a higher risk from congenital deafness and skin cancer.
This is a pattern in which the cat has a solid base color, but the bottom eighth of each hair is white or creamy.
COAT LENGTH AND TEXTURE - Genes involved in coat length and texture
Cat coat length is controlled by the gene named the fibroblast growth factor 5 (FGF5). The dominant allele codes for short coat. Four mutations have been identified in this gene that code for long coat – all of which are recessive. According to the study by Kehler J.S. and co-workers (2007), mutations 1 and 2 were unique to the Ragdoll and Norwegian Forest Cat breeds, respectively, while mutation 3 was found only in Maine Coon and Ragdoll cats. Mutation 4 was the most prevalent mutant in the study and it was detected in all long-haired breeds sampled (Kehler et al, 2007).
Curly coat is produced by various genes. In fact, new types of curly cats sometimes spontaneously occur in freely bred domestics. Some of the identified genes to produce "rex " cats are r (Cornish Rex), gr (German Rex), re (Devon Rex), ro (Oregon Rex) and Lp (provisional). Of all the named genes, only Lp is the dominant allele and it was identified in LaPerm breed. There are many other genes that produce curly divas.
Genes associated with hairlessness have also been identified. In Peterbald and Russian Donskoy, dominant allele Hp was identified to cause this trait. In British hairless cats and French hairless cats, recessive alleles hd and h, respectively, have been noted to be linked to the character. And, in Canadian Sphynx cats, hairlessness is controlled by the recessive hr allele.
The genetics of the feline coat is an extremely complex but peculiar issue. So many identified genes are involved in making every feline just as special and unique as they are. There is so still much more we are yet to discover what lies in the roots of our companion’s coats. We hope we succeeded to offer you a little bit of a deeper and clearer view into the fluffiness of your kitty.