Cat Genetics

[Linsey]

AA, Aa = agouti - tabby pattern (for example black classic tabby)
aa = non-agouti - no tabby pattern (for example black)

BB, Bb, Bb1 = black (non-chocolate)
bb, bb1 = chocolate
b¹b¹ = cinnamon

CC, Ccb, Ccs = Full color (solid)
cbcb = Burmese
cscs = Siamese Pointed Colour
cbcs = Tonkinese Mink Colour

CuCu, Cucu = curled ears (American Curl)
cucu = normal ears (straight ears)

DD, Dd = non-dilution (black, chocolate, cinnamon, red)
dd = dilution (black is blue, chocolate is lilac, cinnamon is fawn, red is cream)

DmDm, Dmdm = dilution-modifier (blue, lilac and fawn are caramel, red is apricot)
dmdm = normal dilution

FdFd, Fdfd = folded ears (Scottish Fold)
fdfd = normal ears (straight ears)

HH, Hh = normal hair
hh = hairless (Sphynx)

II, Ii = color inhibitor (chinchilla, silver, smoke)
ii = normal color

LL, Ll= short hair
ll = long hair

MiMi, Mimi = Mitted
mimi = Solid

Mm = Manx (no tail)
mm = normal tail

RR, Rr = non-Rex
rr = Rex I (Cornish and German Rex)

ReRe, Rere = non-Rex
rere = Rex II (Devon Rex)

RfRf, Rfrf = non-rufused
rfrf = rufused (reddish/rusty touch to the color)

SS= bicolor I (Van or harlequin bicolor)
Ss = bicolor II ("normal" bicolor)
ss = non-bicolor (solid)

SaSa, Sasa = normal hair
sasa = satin (Siamese and other Oriental cats)

SeSe, Sese = Selkirk Rex (Selkirk Rex)
sese = non-Rex

SpSp, Spsp = Spotted tabby -Breaks classic and mackerel tabby up into spotted tabby normal pattern (classic or mackerel)
spsp = not spotted

TaTa, Tat, Tatb = ticked tabby
tt, ttb = mackerel tabby
tbtb = classic tabby

WW, Ww = white (dominant white (this gene is epistatic (dominant) to all other colors as it will mask them)
ww = non-white

WbWb, Wbwb = wide band gene
wbwb = normal "band" width

WhWh, Whwh = wirehair (American Wirehair)
whwh = normal hair

xx = female, non-red (any other color than red or cream)
xy = male, non-red (any other color than red or cream)
xx^o = female, tortie (tortie)
x^ox^o = female, red (red or cream)
x^oy = male, red (red or cream)

[Linsey]

Agouti
Gene A (agouti) is dominant to a (non-agouti). Basically, agouti means tabby. Each hair is ticked with two or, preferably, three bands of black and yellow. The different tabby patterns will be explained later.
Gene a (non-agouti) is recessive to A (agouti). This is a mutation of the agouti gene which makes the yellowish parts of the hair black so that the cat appears as solid colored.

Brown
The gene b for chocolate is a mutation of the normal gene B (black). The cinnamon gene (b1) is a mutation of the the chocolate gene b. Cinnamon b1 is totally recessive to the other two, chocolate b is dominant to cinnamon but recessive to black, and black B is dominant over both.

The chocolate gene can have undesired effects. If a black cat carries the chocolate gene the fur may have a "rusty" shade, or it can cause brownish-shaded points, red-blue eyes or pinkish paw pads in blue-point cats.

The cinnamon gene can have a positive effect on chocolate or chocolate-point cats. Often the chocolate color is too dark when the cat is a purebred chocolate (bb). If it carries the cinnamon gene (bb1) the coat color often has the desired chocolate-brown, not too dark touch.

The albino factor
The natural, unmutated gene is C and means full (solid) color. Several mutations of this gene cause different degrees of points: the Burmese, the Tonkinese and the Siamese.

The point gene (Siamese) cs allows only the coldest parts of the body to develop a color (on face (= mask), ears, legs and tail). If a pointed cat is let outside on cold days it causes the coat to become darker, which is not desirable for a show cat. Pointed kittens are always born white. The color on the points begins to develop after a few days until the cat is full-grown.

Pointed cats always have blue eyes. The eye color of Siamese cats is a very intensive blue (also called Siamese-blue, Turner-blue or China-blue) that was achieved through long and selective breeding. Other pointed cat breeds (for example colorpoint Persians) may have a very light blue eyes. Breeders try to get the same Siamese-blue eye color for these cats, too.

When the eyes of a blue-eyed cat look reddish, this is often caused by a (probably hidden) gene for chocolate (see "brown" above).

Pointed cats that have the agouti gene (see "agouti" above) have tabby points. However, the non-point-part of the coat will show tabby ghost markings (undesirable effect) unless the cat is a ticked tabby (see "tabby patterns" below). You can see this very well in the blue-eyed snow Bengal cat, which is actually a tabby-point.

The Burmese gene is cb which creates a brownish coat for a genetically black cat (sable Burmese). The points (face (mask), ears, legs and tail) are very dark brown and the rest of the body has a warm, sable brown color.

Burmese cats have a yellow-golden eye color that was greenish-yellow in the beginning but has been intensified through selective breeding.

Burmese kittens are born with a lighter color than the actual coat color and will become darker (especially on the points) until they are adults.

The Burmese gene is a kind of variation of the point gene (cs). The cat is not completely pointed like a Siamese but it isn't solid colored (C) either.

A mixture of those two is the mink gene (Tonkinese). It isn't a seperate gene but a combination of the point gene and the Burmese gene (cbcs). The color in the points is the same as the Burmese point color and the Siamese point color, but the body color is neither Burmese not Siamese. It's a mixture of both -- too dark for Siamese and too light for Burmese. The eye color is again a mixture of Siamese and Burmese eyes, a blue-green color.

When you breed two mink Tonkinese cats together you'll get the following results: one half of the litter will be mink colored, one quarter will be "solid" colored (actually this is Burmese color, but they are called "solid") and one quarter will be pointed (please note that the numbers are only theoretical and can be totally different in reality). Some kittens get the cb gene from both parents which will give them a Burmese color, some will get the cs gene from both parents, which will make them pointed, and some will get cb from one parent and cs from the other, and so they are mink colored. (Important: a pointed or Burmese colored Tonkinese is not Siamese or Burmese! It is a Tonkinese and will remain a Tonkinese, no matter what color it has. Only a purebred Burmese is a Burmese, and the same goes for Siamese, although there are some allowable outcross breeds for Siamese, but the Tonkinese is none of those.)

The solid color gene C is dominant over all others mentioned above. cb and cs are so-called "multiple alleles" which means there are several gene mutations for the same trait. In this case, the gene for the Burmese color has an incomplete dominance over the point gene (which means the point gene shows through to a certain degree). However, they are both recessive to the C gene.

Curled ears
The mutated gene Cu for curled ears (American Curl) is dominant over the normal, straight-ear gene cu. Unlike the fold-ear gene (see "folded ears" below) the curl-ear gene is not associated with any genetical defects and American Curls can (and must) be purebred.

Dilution
This gene d is also called "maltese dilution" and recessive to the non-dilution (density) gene D. d will dilute a black cat blue, a chocolate one lilac, a cinnamon one fawn and a red one cream.
If the cat is agouti and diluted (AAdd or Aadd) the yellowish parts of the hair will be beige-cream colored, which creates an interesting effect in ticked tabbies, especially for blue and lilac.
An undesirable effect of the dilution gene is that it can create a cold color if the cat carries the d gene (Dd). For example, the chocolate color should be a warm color, which can be affected by the dilution gene and turned into a cold brown, which is not desirable.

Dilution modifier
The (dominant) dilution modifier (Dm) is a mutation of the normal (recessive) gene dm. It only works when there is already a dilution. That means, if the cat doesn't have dd the dilution modifier will not work. Therefore, black, chocolate, cinnamon and red cats will be unaffected by this gene. However, if the cat has a diluted color (blue, lilac, fawn or cream) and also the dilution modifier Dm the colors will change as follows: blue, lilac and fawn cats will be caramel, cream cats will be apricot.

Folded ears
The fold-ear gene Fd is a mutation of the normal straight-ear gene fd and dominant. Unfortunately, it is associated with genetical defects like deformation of the hind legs or tail when the gene is homozygous (FdFd). Therefore a fold-eared cat must always be bred with a straight-eared partner, so that the gene comes heterozygous (Fdfd).

Hairless
The gene h is a recessive mutation of the normal H gene and causes hairlessness, as you can see in Sphynx cats. However, those cats are not completely hairless but the coat is so short that it is not apparent. The kittens may have some longer fur on the head, the legs and the tail that they will lose later.

[Linsey]

Silver
The gene I is called color inhibitor and is a mutation of the normal gene i. It causes several degrees of silver and is dominant.

Silver basically means that the tip of the hair has color and the rest doesn't. This is called "tipping". There are three degrees of tipping: smoke, silver shaded and chinchilla. All silver cats can be homozygous (II) or heterozygous (Ii) for silver (no visible difference). All silver cats must be non-rufused (RfRf or Rfrf; see "golden" below).

The white part of a smoke's hair is very small (one third). The cat looks almost black when it doesn't move. Only when it is moving (or when the hair is very long as in Persian cats) you can see the silver ground shining through. Kittens sometimes have ghost markings that should disappear during the development.

The main difference to silver and chinchilla cats is that smokes are always non-agouti (aa). The wide band gene seems to have no effect on smokes (see "wide band gene" below), so they can be either WbWb, Wbwb or wbwb.

There are two kinds of silver shaded: the normal silver shaded and the silver tabby. The white part of a silver shaded takes two third of the cat's hair. The silver tabby looks like a normal tabby but with white instead of yellow on the hairs. Actually, a silver shaded is a silver tabby, too, but you can't see the tabby pattern because of the high percentage of white on the hair. The pattern "blurs" on the white underground.

What makes a silver tabby a silver shaded is the wide band gene (see "wide band gene" below). Silver tabbies don't have it (wbwb). Silver shadeds are heterozygous for wide band (Wbwb). That means you could get silver tabbies from a shaded x shaded mating (because the kittens may inherit a wb from both parents, which makes them wbwb and thus silver tabby).

Chinchilla cats have a color tipping of 1/8 of the total hair length which makes them look almost white.

Chinchillas are homozygous for the wideband gene (WbWb).
Here is a handy overview list with all the silver types and the relevant genes:
(a dash (-) means the second gene could be either dominant or recessive)
Smoke: aa I- Wb- or wbwb Rf-
Silver shaded: A- I- Wbwb Rf-
Silver tabby: A- I- wbwb Rf-
Chinchilla: A- I- WbWb Rf-

Summary: The degree of silvering is determined only by the Wideband gene. Inhibitor gene and agouti gene must be present (I and A). Smoke can have any kind of Wideband genes, but must be non-agouti. Note that all these have no rufusing.

Longhair
The recessive longhair gene l is a mutation of the normal, dominant shorthair gene L. Longhair and shorthair both exist in a variety of length, texture and density which are not caused by different genes but by selective breeding. A Persian or Himalayan has the same gene for hair length as for example a Turkish Angora although the Persian coat is much longer and fuller. A hundred years ago a Persian coat looked like the one of a Turkish Angora.

Manx
The gene for taillessness (M) is a dominant mutation of the m gene which stands for "normal tail". There are three types of Manx cats: the rumpy, which has absolutely no tail, the riser (or rumpyriser) which has a few vertebrates that can be seen or felt as an upright projection, and the stumpy, which has an extremely short, often kinked tail, also seen in the Japanese Bobtail.

Rumpy and riser cats are caused by the Manx gene M, stumpy probably not. The inheritance of the different tail lengths is not completely clear. Several other polygenes seem to play a role here. An important fact is that two rumpy or riser cats must not be mated because the kittens that are homozygous for taillessness (MM) are born dead (lethal factor). However, the stumpy tail of Japanese Bobtails and stumpy Manx cats doesn't seem to cause any problems. Therefore rumpy or riser Manx cats must be bred with stumpies in order to get heterozygous kittens (Mm). Such a mating will produce both stumpies and rumpies/risers.

Cornish and German Rex
Rex cats are known for their unique curled fur. There are three different types of Rex cats which are all caused by different genes: the Cornish and German Rex (same gene), the Devon Rex and the Selkirk Rex.

Gene I is for Cornish and German Rex. Their coat is produced by the recessive gene r.

Devon Rex
Rex gene II is called re and also recessive. The structure of the coat is different from the Cornish/German Rex fur.

Golden (the rufusing gene)
The golden color is closely linked with the silvers (see "silver" above). Basically, a golden is like a silver, just with a warm cream color (not related to the x-linked red gene, BTW!) instead of white, with colored (black, blue, chocolate etc.) hair tips, just like in silvers. The difference between silver and golden is determined by the rufusing gene rf (Rufusing or Rufism = Usually undesired reddish/rusty touch on a cat's coat).

The different degrees of golden go just like the silvers. The only difference to the silvers is that the goldens have the rufusing gene (rfrf).

Here is a handy overview list with all the golden types and the relevant genes:
(a dash (-) means the second gene could be either dominant or recessive)
Golden smoke: aa I- Wb- or wbwb rfrf
Golden shaded: A- I- Wbwb rfrf
Golden tabby: A- I- wbwb rfrf
Golden shell (chinchilla): A- I- WbWb rfrf

Note: The rufusing gene also affects cats that are not silver! If you have a non-silver cat that is rfrf, it will have a reddish/rusty touch to its color, and in case you get rfrf in a mating, you'll have to draw your cat with a reddish tinge, and it would have to be neutered, since it's pet-quality, not for breeding or showing.

White spot gene
The white spot (bicolor) gene is dominant (S). There are three main types of colored-and-white cats:
If about one third of the coat is white the cat is a bicolor. This is caused by a heterozygous gene combination (Ss).

If the cat is homozygous for the bicolor gene (SS) the amount of white is more than two third of the cat and called harlequin or van. Harlequin cats have one or several spots of color on the body, the color of the van is limited to the head and the tail. Van cats sometimes have light blue eyes or two different eye colors.

The breeding of colored-and-white cats is difficult because the places where the white color shows up is more or less random. Unknown polygenes seem to play a role, too.

When the cat is tortie and bicolor (calico) the usual small red patches become big and have a clear contrast.

[Linsey]

Satin hair
The extremely short, shiny, satin-like fur of Oriental cats (Siamese, Oriental Shorthair, Balinese, Oriental Longhair) and Burmese/Bombay is based on the recessive gene sa. They have minimal or no undercoat at all.

Selkirk Rex
The Selkirk Rex gene is the third Rex gene. It is a dominant gene (Se).

Spotted Tabby
There are two types of spotted tabby cats. One type has the classic tabby pattern "broken up" into spots, and the other one the mackerel tabby pattern "broken up" into spots. The gene that causes this is dominant (Sp). It doesn't have any effect on ticked tabby cats, since those usually don't really have a pattern at all. If the cat is spsp it will have the usual classic or mackerel tabby pattern.

Tabby patterns
The inheritance of the different tabby patterns is not completely clear and there are several theories about it. This is the one that makes the most sense and is easy to use:
The genes for the tabby patterns are multiple alleles (like Burmese/pointed). Every cat has a tabby pattern, but it will only be shown when the cat also has the agouti (A) gene. Black markings on brownish-yellow ticked ground are often wrongly called "brown tabby" although there is no gene for brown (chocolate). The name of the tabby color is based on the color of the markings, not the agouti-color between!

The most recessive gene is the classic tabby gene tb. When homozygous, it will create a classic tabby pattern (also called marbled or blotched tabby).

The mackerel tabby gene t is dominant to classic tabby (tb) and will create a mackerel tabby cat, no matter if it is homozygous (tt) or heterozygous (ttb).

The most dominant gene is Ta. The cat will be ticked tabby if it's either homozygous for Ta or heterozygous (Tat or Tatb).

A homozygous ticked tabby (TaTa) will (in most cases) show no markings at all, which is desirable especially for Abyssinians.

For spotted tabby see "Spotted Tabby" above.

White
When you have a white cat you'll never know what color it really is, since the dominant white gene W is epistatic to all other colors and will mask them. Only the original eye color will remain. That means if the cat was a blue- or odd eyed (van) before, it will now become a blue- or odd-eyed white.

White is often associated with inheritable deafness, which is thought to be caused by an existence of the white spot gene (bicolor). Unfortunately, you can't see if the cat carries a bicolor gene or not (as I said above). Therefore white cats must only be bred with non-white partners that are not bicolor to exclude the possibility of deaf kittens.

However, there is an exception. White Siamese cats (Foreign Whites) have been bred very long by a detailed breeding plan, which only involves Siamese cats. Since Siamese and none of the allowable outcross breeds are ever bicolor, there is no risk of deafness, so Foreign Whites may be mated. The same goes for white Oriental Shorthairs and the longhair versions.

Wide band gene
The function of the wide band gene Wb has to do with the silver gene (see "silver" above). It determines whether a silver cat will be chinchilla (WbWb), silver shaded (Wbwb) or silver tabby (wbwb). It seems to have no effect on smokes.

Wirehair
The wirehair gene is dominant (Wh). It causes a rough texture of the coat, which is called "wirehair". This mutation is seen in the American Wirehair.

Red and tortie
Red is a so-called sex-linked color. A female cat has the gene combination xx, whereas a male cat has the gene combination xy. The gene for red (o) can only be carried on the "x" gene. That means a female cat can have two o's, a male cat can have one. The "y" is "unused".

Red cats often show tabby ghost markings, even if they are non-agouti. That's why breeding of red cats is so difficult.
Basically, x means non-red (any other color than red -- cream is red, too, it's just diluted) and xo means red. So a male cat can either be red or non-red, since it only has one x (this is called "hemizygous").

A female cat has two x's that can both be red and non-red. This is how the tortie color is "created". When one of the x's is red and the other one non-red, red and non-red patches will be spread randomly all over the body. This is what we call tortie.

If the tortie cat is also bicolor, the small patches will be formed into clearly contrasting areas of red and non-red. This is also known as "calico".

Actually, male tortie cats do exist, but only if there is an abnormality in the sex-determining genes. This is called "Klinefelter" and extremely rare, so don't expect to get one in one of your litters. If so, he would be no use to you, since such males are always infertile because of the abnormality. The gene combination would be xxy, which means the cat would have three genes instead of two.