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Ricki

April 2000, What color was Ricki's father? Part 2

Last month, I began looking at the genes that control the coloration of cats in an effort to figure out what color the father of my cat, Ricki, was. Ricki is a Tortoiseshell, and her mother, Ashley, is all gray. Ricki must have had some color influence from her father, but what?

Ashley

Previously, I discussed the black pigmentation gene, B, and its mutation b (for chocolate), and the dense pigmentation gene which controls how the pigment granules are packed in each hair (D = densely packed; d = dilute). Now, for the rest of the story…

As mentioned, the A and T genes work together to produce the tabby. The Tabby (T) gene is responsible for four different types of tabby patterns: striped (or mackerel), spotted, blotched (classic), and Abyssinian. The Agouti (A) gene controls the color of the background. It can be grayish, yellowish gray, or reddish-yellow, and is composed of hairs that are banded with varying amounts and intensities of yellow. A has mutated to a (non-agouti). Non-agouti lacks the yellow band to the hairs, thereby producing a self-black cat. That is, the black pigment is distributed along the entire length of the hair in the background so the background is black, and the tabby pattern doesn’t show up.

A cat with AATT is a striped tabby, and AA t^bt^b is a blotched tabby; however, aaTT and aat^bt^b are both black. What this means is that the mutated form, a, will obscure the effects of the T gene, except there may be some residual, ghost tabby pattern if the cat’s coat is seen in full light.

The Reader’s Digest Illustrated Book of Cats makes this additional point concerning tabby patterns in red (orange, cream, or yellow) cats: "It is practically impossible to obtain a solid red or cream coat, however. All red or cream cats have a tabby pattern to a greater or lesser degree." Apparently, the aa combination hides the tabby pattern for black colors only.

Here are some examples of cat colors with the aa gene combination. There is no tabby pattern in these combinations.

• aaBBDD – black
• aaBBdd – blue (as in the Russian Blue)
• aabbDD – Havana
• aabbdd – lilac

A tabby cat or an Abyssinian, however, has AA (or Aa) and some form of the T gene. (The Abyssinian’s gene is a mutation, T^a.) A blotched (classic) tabby might be A-B-D-t^bt^b in which case the cat is a tabby with black stripes or blotches. If the cat has A-bbD-t^bt^b, it is a chocolate tabby.

The full color gene, C, determines whether the cat has the color in its full intensity, that is, whether the pigment color is at its full strength. (This is not to be confused with D, which controls the density of the pigment granules in a hair.) One mutation is c^s, which causes a Siamese coloration, or full intensity color only at the points. Another mutation c^a is a blue-eyed albino, while yet another mutation, c, is a pink-eyed albino. (You may have heard that some white cats are deaf, but not because of the c gene. Deafness is linked instead to a different gene that causes whiteness, W.)

Perhaps the most interesting gene is the one for red (orange/yellow/cream) pigmentation. The cat is rare in that its O gene is sex-linked. The O gene (or its mutation, o) can only occur on X-chromosomes. Therefore, only female cats can have two O genes. Males will always have only one. (There is an exception to this. The rare, and normally sterile, XXY male can have two O genes because it has two X-chromosomes.)

For the O gene, a male cat can only have two combinations, OY (where Y stands for the Y chromosome which doesn’t have the O gene) and oY. A female cat can have four combinations: OO, Oo, oO, and oo. If only the capital O form occurs, it makes the cat orange. Only little o means the orange pigment is absent, so the cat is black, brown, blue, or lilac (depending upon the states of the B and D genes). Because male cats can only have O or o, they are either red (or one of red’s variations) or black (or one of black’s variations). A female with OO is red (or a variation), and one with oo is black (or a variation).

But females can have an O and an o. In this situation, O does not completely dominate. Instead both red and black pigmentation occurs – in other words, a Tortoiseshell. Ricki is what is called a red and black Tortoiseshell. Therefore she has the following set of genes: B-C-D-Oo (B- means that the combination could be BB, Bb, or bB. C- means CC, Cc, or cC, and D- means DD, Dd, or dD.)

Tortoiseshells come in other color combinations. For example, a chocolate Tortoiseshell is bbC-D-Oo. A blue cream Tortoiseshell is B-C-ddOo, where the density of pigmentation in the hairs is diluted.

I know what Ricki’s mom-cat, Ashley, looks like, so I can guess at her genetic combination.

aaB-C-ddoo

Because Ashley has oo, she gave Ricki an o gene. But Ricki also has an O gene, so the O must have come from her father. And because males can only have one O gene, Ricki’s father was an OY – a red/orange cat (the O gene will override the effects of the B gene). Also, Ricki has a D gene. Ashley has dd, so Ricki’s father must have passed on a D gene. Therefore, he was probably a full color red/orange rather than a cream color.

Because the Reader’s Digest Illustrated Book of Cats says that most red (orange/yellow/cream) cats have at least a little tabby patterning, Ricki’s father probably had some markings. But Ricki has both red and black colors. Does she have any tabby markings? Interestingly, the tabby and agouti genes seem to act a little differently with Tortoiseshells.

According to the Book of Cats, red and black tortoiseshells have aa. The book also goes on to say, on page 145:

"Tabby markings may be present in red and cream areas, especially on the extremities of the cat, but will not be present on the body if the cat’s gene mixture contains the agouti tabby gene. If the eumelanin [black] areas have any tabby patterning, the cat is a torbie."

Ricki does not have any tabby patterning in the black areas, so she must have aa. (Ricki’s father must have had at least one a gene.) But she does have both red and yellow/cream. The Standard Guide to Cat Breeds book says the following:

"The tortoiseshell (aaOo) is a brindled mosaic of black, red, and cream. The variety does not posses three colors, of course; the red is produced by the intense tabby pattern (usually blotched) while the yellow [cream] is produced by the paler areas between the pattern."

Consequently the cream color in Ricki’s coat is not caused by dilution (d), but rather by a tabby pattern.

The one aspect of color, white, is controlled by two genes. The W gene overrides all the other colors and produces an all white cat. A cat with these genes AATTWW is called a white carrying tabby. A cat with aaTTWW is called a white carrying black. But both of these cats look the same, namely all white. If a cat has ww, it is a normal colored cat, although the other white color gene may come into play.

The other gene that controls white is called the Spotting gene, S. A Tortoiseshell and White cat or a Calico cat has an S gene. S does not completely dominate, so Ss has less white than SS. The only white I’ve ever found on Ricki is between the pads of two of her paws, and even then it could be a very light cream, so I don’t know if she has an S gene or not. Ashley has no white, so she is wwss. It is possible that Ricki’s father was a wW cat (or all white), or an sS (bicolor, white and orange).

Ricki’s final gene determination: aaB-C-D-Oossww

Ashley’s: aaB-C-ddoossww

Ricki’s father: aaB-C-D-OYssww, or A-B-C-D-OYS-ww, or aabbC-D-OYssww, or A-bbC-D-OYS-ww, or A-bbC-D-OYS-W-, or A-B-C-D-OYssW-, or A-B-C-D-OYS-W-, or A-bbC-D-OyssW-. But in simple terms – Ricki’s father was most likely an orange cat or an orange and white cat, or possibly a white cat carrying orange. The important gene (in my opinion) is the O. That combined with Ashley’s o resulted in Ricki’s Tortoiseshell Oo.

Nap Time

Gene Symbols