Genes that determine color: A, O, C and E-genes

A-genes: Agouti or non-Agouti

The Agouti gene (denoted by capital A) is the natural wild gene responsible for the tabby (striped) pattern in cats. The Agouti gene is dominant and determines how each individual hair is provided with color. The shape of the stripes or spots on the coat is further determined by the Tabby genes, described further on. As each individual hair grows, the Agouti gene is responsible for the switching between the red-yellow and black-brown pigment resulting in bands of different colors. The tip of a hair is always dark, while the base is light. A mutation of this gene causes it to stop switching to the red/yellow pigment, resulting in a hair with solid or uniform color. We call this non-agouti or “hypermelanistic” and describe it with the lowercase letter (a). Perhaps the best-known melanistic wild cat is the black panther. Non-agouti (a) suppresses or masks the agouti (A) pattern, but the pattern is sometimes still visible with the right light, as seen in the photo of a black panther below. We call this ghost-striping or ghost-markings.

Non-agouti (a) is recessive and thus only visible if a cat inherits the non-agouti gene (a) from both parents. So an A/A or A/a cat (referred to as A/-) is tabby. An a/a cat is uniform of color. Thus, the common black cat is a carrier of two recessive a-genes. So, to what extent a kitten will become tabby or uniform of color depends on what the parents are carrying:

• A/A x A/A ⇒ 100% A/A = 100% tabby kittens.
• A/A x A/a ⇒ 50% A/A + 50% A/a = 100% tabby kittens, but half are melanistic “carriers.
• A/a x A/a ⇒ 25% A/A + 50% A/a + 25% a/a = 75% tabby (of which 2/3 are melanistic carriers) and 25% melanistic kittens.
• A/a x a/a ⇒ 50% A/a + 50% a/a = 50% tabby (and all melanistic carrier) and 50% melanistic kittens.
• a/a x a/a ⇒ 100% a/a = 100% melanistic kittens.

O-genes: Orange

The O-gene provides the orange-red color of cats and is special for two reasons. First, it occurs only in cats and not in other animals. Second, it is present on the X chromosome and thus the orange color is linked to the sex of the cat. The O-gene blocks the production of the black-brown pigment (eumalanin), leaving only orange-red pigment (phaemalanin). Orange (O) is dominant over the recessive non-orange (o).

Females are XX and have two X chromosomes and therefore can have a coat that is completely orange-red (O/O), spotted orange-black (O/o) – known as a tortie or tortoiseshell cat – or have a coat with hairs that have both pigments (o/o). In the latter case, the A-gene determines whether the cat is uniform (black-brown) or tabby in color. Males are XY and have only one X chromosome. Therefore, they can have a completely orange-red coat (Y/O) or a coat with hairs that have both pigments (Y/o), with the A-gene again determining tabby or solid. Tortoiseshell cats are orange-black spotted which requires two O-chromosomes and are therefore always females (with the exception of XXY males which have an extra chromosome).

Another special trait of the O-gene is, that the non-agouti gene (a) is suppressed by the O-gene (in other words the O-gene is epistatic for non-agouti). Therefore, orange-red cats are never uniform in color and are also always tabby. And for red-black tortoiseshell cats, although the black part may be uniform in color, the orange-red part retains its stripes.

C-genes: Color, Colorpoint and Albino

The C-gene controls the pigment generation. The C-gene is completely dominant, and when it is active, the cat can have a full color. A recessive mutation (c) can cause the gene to be completely inactive and no pigment is produced, resulting in a white albino cat (with red or blue eyes). There are also a number of additional recessive mutations that cause colorpoints. The cs (siamese) and cb (burmese) mutations provide temperature-sensitive pigment production. As a result, more pigment can be formed on the cooler parts of the body such as back, feet, face and tip of the tail. So in the siamese (which is cs/cs), this produces the typical pattern of a light color on the body with a dark muzzle, ears, feet and tail. Because these parts are at the end(points) of the body, these cats are called colorpoint. Colorpoint bengals are called “snow. Cb is less temperature sensitive than cs, which is why cb cats have darker bodies. The dominance of this gene is as follows: C > cb = cs > c. The designation of the colors is as follows:

• C/- = full color.
• cb/cb = burmese colorpoint. In bengal: snow seal sepia.
• cb/cs = tonkinese or mink colorpoint. In bengal: snow seal mink.
• cs/cs or cs/c = siamese colorpoint. In bengal: snow seal lynx.
• c/c = albino.

E-genes: Extension or Amber color

The E-gene affects the production of black-brown pigment. In cats, this was first found in Norwegian forest cats. A recessive mutation of this gene (e) causes a gradual replacement of the black pigment with a yellow pigment as the cat grows up, manifesting as an amber coat. Several years ago, a similar mutation of the same gene was found for burmese cats. For burmese, we call the color “russet” (denoted by “er”). The E-gene is less important for cats and more important for dogs and horses, where (e/e) is responsible for the beautiful golden color of the Golden Retriever, the rich red color of the Irish Setter and the noble sorrel/chestnut color seen in horses.

Genes that adjust color: B, D and I-genes + Wideband effect

B-GENES: BLACK (B), CHOCOLATE (b) AND CINNAMON (b1)

The B-gene affects the intensity of the black pigment. Brown is recessive trait that changes the black (B) to a chocolate (b) or cinnamon (b1) color. If you would look at an individual hair under a microscope, the pigment in black cats is round shaped, while in chocolate cats the pigment is oval-shaped and in cinnamon it has the shape of a rice grain, making it appear lighter. B is dominant over b, which in turn is dominant over b1. Black cats are thus B/B, B/b or B/b1 (B/- for short). Chocolate cats are b/b or b/b1 and cinnamon cats are b1/b1.

D-GENES: DILUTION (d) AND DILUTION MODIFIER (Dm)

The dilution gene is a recessive trait that makes the normal color lighter or paler. Cats carrying D/D or D/d show full color. For cats carrying d/d, the colors are modified. Black becomes blue, chocolate becomes lilac, cinnamon becomes fawn and orange becomes cream.

If you would look at an individual hair under a microscope, the pigment in d/d cats is not spread uniformly throughout the hair, but grouped into clusters with little to no pigment between the clusters. As a result, part of the hair is transparent, leading to the lighter color. With a dilution-modifier (Dm) carrier, diluted colors become warmer. Dm only affects d/d cats and not D/D or D/d. Blue, lilac and fawn cats with Dm are given a caramel color tone. Cream takes on an apricot hue.

Regular tabbies are wb and the Wideband is not active. With shaded, less than the (top) half of a hair still has pigment. With chinchilla (also called tipped or shell), only the tip of the hair has pigment left. So wideband can have different gradations and is therefore described by Wb (for shaded) to Wb++ (for strong chinchilla). Wideband also affects black or brown tabby cats, i.e. the non-silver cats. This creates the “gold” color. So a gold shaded or tipped cat is not silver (i/i), but is Wideband (Wb to Wb++). Golden smoke does not exist because smoke is caused by the silver I-gene and not by the Wideband effect.

The silver gene (I) is dominant over non-silver (i). An (I/i) silver male can have both silver and brown kittens as offspring. An (I/I) silver cat produces only silver kittens. To date, the silver gene cannot be tested and therefore it can only be determined from litters produced whether a cat is I/i (if there is ever a brown kitten in a litter) or most probably I/I (if there are always only silver kittens). Below are examples of the silver and gold chinchilla, shaded, tabby and smoke effect for a british shorthair.

There are several genes responsible for Tabby patterns:

Mackerel (Mc) and classic (mc): the mackerel gene provides the striped pattern, while cats with a classic pattern have a marbled coat. Mackerel (Mc) is dominant over recessive classic (mc).

Ticked (Ta): This is a largely dominant gene, which removes the pattern from a mackerel/classic tabby, leaving the cat with a uniform agouti coat. A Ta/ta no longer has stripes on the body, but still has them on the legs, face, neck and tail. A Ta/Ta cat has only visible stripes on its face. A ta/ta cat is not ticked and thus does have a visible tabby pattern.

Spotted (Sp): this denotes the collection of genes (polygenes) that cause, that the stripes of a mackerel are broken up and thus provides spots (as for example of a cheetah). In an Sp/Sp cat, there are complete spots. In a Sp/sp, the stripes are only partially broken up and the spots are still partially connecting. For sp/sp, the stripes are not broken up. Spotted (Sp) has no effect on cats with a classic pattern (mc/mc).

One might wonder, how it is actually possible for a cat to develop a stripe or spot pattern at all. How does a coat “know” that a band or group of dark hairs should be placed in one place and light hairs in a different place? This question remained unanswered for a very long time and only very recently, in 2021, an article appeared in Nature, revealing more about the mechanism responsible for spot formation. It appears that as early as skin formation in the embryonic stage, it is determined where the spots or stripes will be formed. More on this can be read here, here and here.

Bengals can have not only spots, but (donut) rosettes, where the spots in the middle are dark brown with a black ring around them. Or bengals can have a marble pattern, where the classic swirls are broken up and multiple colors can be seen in the marble pattern. An intermediate form is the clouded rozetted bengal, in which the rosettes are very large and lay against each other. How the rosettes are formed and which genes are responsible for them is not exactly known. However, for convenience, this trait is referred to as the Bengal modifier or Bengal markings (Bm), with the modifier for those providing rosettes and marble (Bm) being dominant over the basic mackerel/classic and spotted patterns (bm). Thus, a bengal with isolated rosettes is Mackerel (Mc/-), Spotted (Sp/Sp) and has the Bengal modifier (Bm/-). A bengal with clouded rosettes is Mackerel (Mc/-), has large rosettes that are almost joining (Sp/sp) and and has the Bengal modifier (Bm/-). A marble bengal has a classic pattern (mc/mc) and the Bengal modifier (Bm/-).

• Rosettes: Bm/-, Mc/-, Sp/Sp, ta/ta
• Clouded rosettes: Bm/-, Mc/-, Sp/sp, ta/ta
• Marble: Bm/-, mc/mc, any Sp, ta/ta

Genes for the white coat: W-genes

W-genes: White coat, spots And socks

A cat with a black and white fur is probably one of the most common colors of normal domestic cats. A white coat color, spots or gloves are caused by the fact that the cells that produce pigment (melanocytes) are not distributed to the skin layer during embryonic development, which prevents a hair from being pigmented during growth. This disorder is caused by a defect in the so-called KIT genes. For dominant white (W), there are no pigment-producing cells present in the skin at all, so the coat cannot acquire color. This gene also causes blue eyes and deafness. For white cat with 2 blue eyes, 60-80% are completely deaf. In white cats with 1 blue eye, 30-40% are deaf and in white cats with other eye color, 10-20% are deaf, with the remaining portion often having impaired hearing in varying degrees.

In cats with partially white coats or white spots (Ws), pigment cells spread (only) to part of the skin. In those parts the coat can have its normal color (black, red, tabby etc). The rest is white. Partly white cats do not suffer from deafness. Cats without white fur is denoted by (w). Ws/Ws cats tend to have more white than Ws/W cats. The degree of white on the coat can vary greatly. The Turkish Van only has color on the ears and tail and the rest of the cat is completely white. This is called a Van pattern. Cats with only a few spots are called “harlequin.” Bicolor cats have a greater amount of (irregular) white spots. The pattern of cats that have a black face and a large spot on their back is called “cap and saddle.” When a larger part is black we call it “mask and mantle” and cats that have only a white chest and feet appear to wear a black suit and are therefore called “tuxedo” cats.

Finally, there are cats with only white gloves (wg), which is caused by another mutation. For Birman cats, this has even become part of the breed standard and all Birmans are wg/wg. The white glove mutation wg is fully recessive. The order of dominance of white is: W > Ws > w > wg.

• W/-: all-white cat.
• Ws/Ws: cat with white spots or mostly white.
• Ws/w: same as Ws/Ws, but often less white.
• Ws/wg: cat with white spots and white gloves.
• w/w: normal or non-white cat (apart from albino).
• w/wg or wg/wg: white gloved or mitted cat.

Incidentally, the white gloves in Ragdolls come from another dominant gene (designated Sb, Sm or s2). The effect of this gene are white feet, chin and a white strip on the underside of the body to the tail.

The genes for hair length, curls, hairless, bengal fuzzy and glitter

L-genes: longhair or shorthair

L genes are responsible for coat length. Shorthair (L) is dominant over longhair (l). Therefore, long-haired cats carry two genes of the recessive variant and are l/l. A 2007 study found that hair length is caused by four mutations of the so-called fibroblast growth factor 5 (FGF5) gene. Mutation 1 and M2 are unique to Ragdolls and Norwegian forest cats respectively. M3 was found only in Maine Coones and Ragdolls. M4 was found in all long-haired cats.

Rex mutation for curly hair

Besides shorthair and longhair, there are also cats with curly hair, this is called the “rex” mutation. For cats several mutations are known, including r (in cornish rex), gr (in german rex), re (in devon rex), ro (in Oregon rex), se (in selkirk rex) and Lp (in LaPerm). Currently, only 4 rex cats are internationally recognized: Cornish Rex, devon Rex, LaPerm and Selkirk rex.

H-genes: hairless or bald cats

Finally, there are hairless cats, the most famous of which is the (Canadian) sphynx. For the sphynx, this is caused by the recessive hr (hairless) gene. Other hairless cats include the Peterbald and Russian Donskoy (Don-sphynx), where this is caused by the dominant Hp gene.

Fuzzy phase of bengals

When bengal kittens are about 3-4 weeks old, they develop a longer fluffy coat, which temporarily hides their pattern. This is called the “ugly fuzzy” phase and originates from the wild ancestor, the Asian tiger cat (ALC). For feral cats, the fuzzy is more common. The most clear example is of the cheetah cubs, where the entire back has a strip of long hair, see the photo below. The fuzzy phase increases the chances of survival for wild cats. The fuzzy fur is developed in the same period when the cubs are slowly leaving the nest for exploring. A fuzzy coat provides extra camouflage among the tall grass and it also offers extra protection against bad weather. In addition, a cheetah kitten in the fuzzy phase resembles a honey badger somewhat. A honey badger is one of the most fearless animals and notorious for its uncommon ferocity and fighting spirit, causing hyenas, leopards and even lions to prefer to leave them alone. After about 4-5 months, the bengal coat clears up again, revealing its beautiful pattern. The final color and pattern of the coat is achieved at 12 months of age.

Glitter at bengal

The last feature we will describe in this article is bengal glitter. Where bengal kittens go through an “ugly fuzzy” phase, adult bengals more than make up for this with a beautiful coat that can look like someone sprinkled stardust over it. This is caused by the glitter gene. Unfortunately, not all bengals possess this trait. The color of the glitter depends on the color of bengal. Charcoal bengals have silver glitter, brown bengals have gold glitter and silver bengals have crystal glitter. Melanistic bengals cannot have glitter. Studies show that there are two types of glitter: satin and mica. The recessive satin glitter gene (gn) causes air pockets in the hair, refracting light and giving the coat a soft, silky appearance. There is also the mica effect, in which there are highly reflective silica crystals in the tips of the hair. This is caused by the recessive mica gene (mi). Bengals with satin and mica are thus (gn/gn) and (mi/mi). The glitter effect comes from the Indian male used by Jean Mill in her breeding program: Milwood Tory of Delhi, the primal father of the bengals (see the article on the history of the bengals).

Overview of all genes in a table

All genes responsible for the cat coat colors and patterns are shown in the table below with a breakdown by dominant gene and recessive mutation.

Five examples of the complete genetic description of the cat

All the genes described above collectively determine the colors and pattern of the cat coat. Below are five examples of different cats and which genetic description belongs to each cat.

Testing for coat color can be done at UC Davis

Wondering what color genes your cat has? Testing a cat coat color can be done at several laboratories around the world. One of the best known is the veterinary genetics laboratory at the University of California at Davis in the US. Bengals can be tested for Agouti here (A), charcoal (Apb), Brown (B), Colorpoint constraints (C), Dilute (D) and Amber (E). For our cattery, we also use this lab and the results of the color tests can also be found in the documents for our queens and studs.

References and further reading

https://www.gccfcats.org/wp-content/uploads/2021/09/BasicCatgenetics.January2022.pdf
http://messybeast.com/colours-conformation-index.htm
https://basepaws.com/blogs/news/cat-coat-genetics
https://sparrows-garden.com/genetics.html
https://www.thehappycatsite.com/cat-colors/
https://thelittlecarnivore.com/en/blog/cat-coat-tabby-patterns-genetics
https://www.hdw-inc.com/geneticsofcolors.htm
https://ecoevocommunity.nature.com/posts/how-the-serval-gets-its-spots
https://med.stanford.edu/news/all-news/2021/09/cat-fur-color-patterns.html
https://www.nationalgeographic.nl/we-weten-nu-hoe-cyperse-katten-hun-strepen-krijgen
https://www.nationalgeographic.com/animals/article/how-tabby-cats-get-their-stripes
https://www.nature.com/articles/s41467-021-25348-2
http://ib.berkeley.edu/courses/ib162/Week3a.htm
https://pubmed.ncbi.nlm.nih.gov/27671997/
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4199695/
https://pubmed.ncbi.nlm.nih.gov/17767004/
https://academic.oup.com/g3journal/article/4/10/1881/6025589
https://slideplayer.com/slide/5162101/