Cat coat genetics (part 1)
Please note that you're reading the old version of this article. You can find the updated article here.
Cats come in a highly diverse variety of coat patterns, coloration and textures. Many different genes are involved in creating just how unique your feline companion will turn out to be. Today we attempt to take a narrow glimpse into the role genetics play in your cat’s coat pigmentation, pattern, length and texture. Due to the complexity of the issue, we decided to break this article down into two parts. In the first part we will discuss the coat colors and some of the coat patterns. In the second part we will continue with coat patterns, lengths and textures.
Summary of the most important coat color genes
1. Brown, chocolate, cinnamon and similar coat colors are products of the feline primary gene for coat color – gene B/b/b1. This gene codes for eumelanin pigment. Dominant allele B codes for black color, b for chocolate and b1 for cinnamon. The intensity and pattern of these colors depends on the other genes involved in formulating the final feline phenotype.
2. The co-dominant red gene O/o found on the X chromosome determines whether there will be any red variations to fur color or not. The allele O codes for orange tones, and the allele o for the non-orange pigmentation (black or brown). Because males have just one copy of the X chromosome, they can carry only one of the alleles of this gene – either O or o. If they carry the allele O, they will be red, orange or creamy (depending on the variation), otherwise, they won’t have any orange tones to their fur. Females have two X chromosomes which means they will carry two alleles of the gene. If they are dominant homozygotes (OO), they will be red toned, recessive homozygotes (oo) won’t have any orange tones and heterozygotes (Oo) will be tortoiseshell (more about this in Part 2 of the article).
3. Dense/dilute pigment gene, D/d, codes for melanophilin. This gene alters the original coat pigmentation by affecting the deposition of the pigment in the hair. If a cat is a recessive homozygote dd, then the black cats will appear grey, the brown will be lilac, the cinnamon will become fawn, and the orange cats will turn cream. Dominant homozygotes DD and heterozygotes Dd are not affected.
4. The C/c/c1 gene codes for the tyrosinase enzyme. The dominant allele C codes for a fully functionable protein and all the carriers will show full coat pigmentation. The recessive alleles code for a mutated tyrosinase and result in one of the two forms of albinism: complete and temperature sensitive (more about this in "White cats").
5. A white spotting gene S/s causes white spots or patches on the coat and can highly vary in expression. Dominant homozygotes SS typically express extensive white patching compared to the heterozygotes Ss. Recessive homozygotes ss don’t express any white spots in the coat. This gene produces white, unpigmented patches by delaying the migration of the melanocytes to the skin surface.
6. The dominant allele W of the white masking gene causes disrupted replication and migration of melanocytes into the skin. 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.
Guide through cat coat patterns and colors
Bicolor, Tuxedo or Van
This is a coat variation in which the cat has one primary (non-white) color with white parts. The pattern varies from Tuxedo – when the cat is mostly black with a little bit of white on its chest, to Van – mostly white with colored tail and top of the head. The base color can be black, red or tortoiseshell. It is the white spotting gene (S/s) that causes the white spots or patches in the fur. Dominant homozygote SS expresses more extensive white patching compared to the heterozygote Ss.
Tabby divas have marbled pattern consisting of butterflies, bullseyes, stripes, spots or swirling patterns. Their forehead is also often marked with an "M" shape. Taking a closer look at a single hair of a tabby can reveal that it’s banded with different colors. This pattern is the result of the dominant allele of the agouti gene (A). The agouti gene allows full pigmentation when the hair first starts to grow, then it slows down the synthesis of the pigment, and then speeds it up again. This creates the pigmented bands along the hair. The agouti banding can be observed in both eumelanistic (black-based) and phaeomelanistic (red-based) coats.
The recessive allele of this gene is called non-agouti. Only recessive homozygotes for this gene (a/a) will result in solid coloration. The tabby pattern of the coat, however, is determined by the tabby gene. This gene is what will cause these banded hairs to alternate with stripes, spots or solid patches. There are four tabby patterns recognized: mackerel, classic, spotted and ticked. Tabbies can also be a part of another basic coat pattern such as calico or tortoiseshell.
The four tabby patterns:
1. Mackerel tabbies, or popularly known as "fishbone tabbies", are characterized with vertical stripes on the sides. The narrow lines can be continuous or broken into bars and spots on the flanks and stomach. This is the most common tabby pattern.
2. Classic tabbies, often nicknamed as "blotched" or "marbled", sport swirled patterns on their sides. On the shoulders there is a light "butterfly" pattern, and three thin stripes down the spine.
3. Ticked tabbies are stripe-less. They have bands of colors and sand-like appearance.
4. Spotted tabbies have stripes broken down into smaller or larger spots. This pattern is often observed among Bengal, Serengeti, Egyptian Mau, Arabian Mau, Maine Coon and other breeds.
The genetics behind the feline coat is undoubtedly a curious case. Yet, we are just getting started! In the next part of this article we will continue with more coat patterns, lengths and textures. Make sure not to miss it!