Cat colors
The cat colors are caused by the presence of melanin. Melanin is a skin pigment and can have different shape and size, giving a variety of colors. There are two kinds of melanin: eumelanin and phaeomelanin. Eumelanin pigments have a spherical shape and absorb almost all light, giving black pigmentation. Phaeomelanin pigments have an elongated shape, and reflect light in the red-orange-yellow range.

The color density gene: Solid and Dilute

Solid is refered to with the capital letter B, and it is dominant over b, the dilute form.
These genes can combine in 4 different ways, even if phenotipically they will show just as solid OR dilute.
Here is a simple tableto help you understand how it works:

B is dominant over b, so in 3 of the above cases the cat will be solid (BB, Bb, bB), in just one case will be dilute (bb), when both recessive genes will be present at the same time.

The black gene

The gene for black is called B, and it is dominant over b and bl.
B in the omozigous or eterozigous form gives the color black, b is the reccessive gene that gives the color chocolate, while bl gives the color cinnamon.

B is dominant over BOTH b and bl, while b is dominant on bl. This means that a cat with genotype bbl will show the chocolate color, and carry the cinnamon one. In order to have a cinnamon colored cat we need the gene bl to be present in both alleles.
Black, chocolate and cinnamon in the dilute form are called blue, lilac and fawn.

So, how do these genes combine with the D gene responsible for solid and dilute?
• DD – full color
• Dd – full color
• dD – full color
• dd – dilute color

Combining the black pigment gene (B) and the density gene (D) gives 16 combinations. Here are some examples.
• BBDD – black
• BbDD – black
• BbDd – black
• bbDD – chocolate
• bbDd – chocolate
• BBdd – blue (gray)
• Bbdd – blue (gray)
• bbdd – lilac
• bblDD – chocolate
• blblDD – cinnamon
• blbldd – fawn

The agouti gene

This is the gene responsible for tabby.
A is responsible for the presence of the tabby markings in a cat, and it is dominant over a, the gene responsible for the not-tabby pattern.
The different marking types are due to other genes:

Ticked Tabby

Ta/Ta Homozygous - Ticked Tabby Ticked Tabby
Ta/ta Heterozygous - Ticked Tabby Ticked Tabby
ta/ta Homozygous - Non Ticked Tabby No Effect
Ticked tabby allele is a dominant modifier to all other Agouti variations. The cat must have ta/ta to see the other variations. E.g., TA/ta, SP/sp, Mc/mc = is a ticked tabby carrying non ticked tabby and masking Spotting, carrying non spotting and masking the Mackerel tabby allele that carries the classic tabby allele.

Spotted tabby

Sp/Sp Homozygous - Spotted Tabby Spotted Tabby
Sp/sp Heterozygous - Spotted Tabby - carrying non spotted Spotted Tabby
sp/sp Homozygous - Non Spotted Tabby No effect
The Spotted Tabby allele is a dominate modifier of both the mackerel and classic tabby allele, but is recessive to the ticked tabby modifier allele. e.g. ta/ta, SP/sp, Mc/mc = Spotted tabby carrying non spotting allele, masking the mackerel tabby allele carrying the classic tabby allele (with no ticking)

Mackerel/Classic tabby

Mc/Mc Homozygous - Mackerel Tabby Mackerel Tabby
Mc/mc Heterozygous- Mackerel - carrying Classic Tabby Mackerel Tabby
mc/mc Homozygous - Classic Tabby Classic Tabby Markings on coat
Both Mackerel and Classic tabbies are modified by ticked tabby allele and the spotted tabby allele. They must have non ticked (ta/ta) and non spotted (sp/sp) alleles present in order to allow the Mackerel/Classic tabby allele to display its phenotype, e.g.: ta/ta sp/sp, Mc/mc = mackerel tabby carrying classic tabby allele (with no ticking or spotting).

The Colouration gene

C is a particular gene with a wide range of recessive variations.
The dominant gene C will provide a normal colored cat.
The recessive forms are quite a lot, so just see them one by one:

- ca is the gene responsible for blue eyes albino (ca ca)
- c is the gene responsible for red eyes albino (c c)
- cs is the gene responsible for the colorpoint (siamese) color. The presence of cs in both alleles (cs cs) will modify the coat color giving a pale beige coloration on all body, excepted for the points (head, tail, paws). The eyes color will be blue.
- cb is the gene responsible for the sepia (burmese) color. The presence of cb in both alleles (cb cb) will modify the coat color giving a bit paler body color than solid cats. The eyes color can vary in color, even if they are often yellow, green or very pale blue.

But… how these genes combine if present at the same time ?
The ca and c genes are VERY rare. ca and c are both recessives to cs and cb.

The cs and cb genes are quite common, and there are breeds allowed if only of these colors. Like the seamese breed, allowed only in the colorpoint (cs cs) color. And the burmese breed, allowed only in the sepia (cb cb) color.

But what if both the cs and cb genes are present at the same time?
We will have a cat with cs cb genotype. When both these genes are present we get a NEW color because cs and cb are co-dominant to each other.
This particular coloration is called mink, or tonkenese (from the breed name with this typicall coloration).
A mink (cscb, cbcs) colored cat will have an intermediate coloration between colorpoint and burmese.
The body color will be then darker than a colorpoint, but lighter than a burmese.
The eyes color will be a aqua, or pale blue.

We may now clarify a few points that are often not clear to many newbies !
A cat cannot be both point and mink.
A point cat will have cs cs genes, a mink one will have cs cb, while a burmese one will have cb cb.
A cat cannot carry mink, as mink is referred to the COUPLE of genes cs and cb when together. If these genes are present together, we get a mink colored cat. There is no chance then for a cat to carry mink…. And actually not be of that color. A cat can be a point carrier OR a burmese carrier.

Here are few examples to better understand what we would get with different breedings:
Normal colored (C C) x Point (cs cs) -> All kittens will be normal colored, but all them will carry the point gene (cs)
Normal colored (C cs) x Point (cs cs) -> 50% of the kittens will be normal colored (C cs), 50% will be point colored (cs cs)
Point (cs cs) x Sepia (cb cb) ? All kittens will be mink (cs cb)
Point (cs cs) x Mink (cs cb) ? 50% of the kittens will be mink (cb cs), 50% will be point (cs cs)
Mink (cs cb) x Mink (cs cb) ? 50% of the kittens will be mink (cb cs), 25% point (cs cs ), and 25% sepia (cb cb)
Mink (cs cb) x Sepia (cb cb) ? 50% of the kittens will be mink (cb cs), 50% sepia (cb cb)

The white gene

The W gene is responsible of the white coloration.
It is a dominant gene that “hides” any other coloration. So a completely white cat appears as white, but is genetically of another color…. Maybe black, or tortie…
W is dominant over w.
So in order to have white kittens, you surely need a white parent :-)

The white piebald spotting gene

The Piebald allese dispays variable expressions, such as an all almost white cat, and an almost not white cat, with just a white toe !
The S gene is dominant and is responsible of the presence of a variable quantity of white spots on the cat’s coat. The quantity is only in part due to the presence of 1 or 2 dominant genes:

Here is a very good article about ALL types of white or with white colors !
http://home.earthlink.net/~featherland/off/white.html

The Inhibitor gene

The inhibitor gene I is responsible of the silver and smoke colorations, while the recessive form i is responsible of the not-silver/smoke colored cats.
The color is called silver tabby when the gene I is present together with the agouti gene (A).
The color is called smoke when the gene I is present together with the recessive form of the agouti gene (a a). The color of the hair is partially white, giving that silverish color appearing.
Chinchilla/shaded/tipped are also inhibitor agouti combination but with the addition of wide banding on the hair shaft.

Red, the sex linked gene

Red, referred as to O is a sex linked gene.
It means that it is present on the X cromosome, and leads to an interesting result !
The O gene is dominant over o (not red).

A female has two X cromosomes: X X
While a male has just a X chromosome and a Y one: X Y
Just talk about males.
They have only a X chromosome, so it’s quite easy… if they have the red gene in the dominant form (O) on the X chromosome they will be red in presence of the solid D gene, or cream in presence of the recessive form of the solid gene (d d). If the red gene O will be present in its recessive form (o o) the cat color will show up not red.

With females it’s all a bit more difficult.
A female can have the red gene O on both chromosomes, or just on one of them.
When the O gene is present on both X chromosome it works exactly as with males. So we will have a red or cream coat.
If the O gene is present just on one of the X chromosome we will get a tortie. A tortie is a cat with two colors together: red and black (in case we have the D gene) or cream, blue (in case we have the d d genes).

Here are just a few examples to make a bit clearer the coat color genotype.
When we don’t know wether a cat carry a certain recessive gene, it is referred to as x.
For example: we have a black cat, but we don’t know if this cat is a dilute carrier. We will write down him genetically as Dx (as in reality we don't know wether the cat is DD or Dd)

What’s the genotype of a:

Silver blue tabby -> dd (is dilute) Cx (is normal colored) Bx (is black) Ax (is tabby) Ix (is silver) oo (is not red) ww (is not white) ss (has not white spots)

Chocolate point -> Dx (is solid) cs cs (is pointed) b b (is chocolate) aa (is not tabby) ii (is not smoke) oo (is not red) ww (is not white) ss (has not white spots)

Silver tortie tabby with white -> Dx (is solid) Cx (is normal colored) Bx (is black) Ax (is tabby) Ix (is silver) Oo (is tortie) ww (is not white) Sx (has white spots)