This article is from the Miscellaneous Cat Information FAQ, posted to rec.pets.cats newsgroup. Maintained by Cindy Tittle Moore with numerous contributions by others.
A cat with patches of red and black is a tortoiseshell, or 'tortie'. Add white, and you get a calico. A tortoiseshell that is homozygous for the recessive 'dilution' gene is referred to as a blue-cream, and that's what color it is: patches of soft grey and cream. This is the same gene that turns black cats 'blue' (grey), and red cats cream. A blue-cream and white is generally referred to in the cat world as a dilute calico. The pattern of black/red or blue/cream can either be in big dramatic patches, brindling, or some of both. Having more white seems to encourage the formation of the big patches.
Red in cats is a sex-linked color, carried on the X gene. Therefore, a male cat whose X carries red will be a red tabby. A female cat who carries one red and one non-red X will be a patched tabby, a tortoiseshell, or a calico (if she also has the dominant gene for white markings). A female cat who is homozygous for red (has it on both X genes) will be a red tabby. This is why you see more male red tabbies than females. This is also why male calicos are so rare: you have to have two X genes to be a calico. Male calicos have genetic aberrations of various sorts, of which XXY is most common. While they are most commonly sterile, there *are* documented cases of fertile male calicos. However, the generalization that "all calicos/torties are female" is true 99.999 percent of the time.
The reason red females are "uncommon" is that, statistically, the number of red males is equal to the number of tortoiseshell/calico, patched tabby, and red females. Red males and tortie/calico/patched tabby females can be produced when only one parent has the red gene, but to produce a red female, you must cross a red male with a red/tortie/calico/patched tabby female. That is why red females are uncommon. But not "impossible", in the sense that a male calico is "impossible."
A "solid red" cat will always display the tabby pattern (although it may be very slight or even undetectable without brushing the fur back to check). There's another gene at work which controls "agoutiness" (whether individual hairs are banded or solid). Cats who are non-agouti will not generally display the tabby pattern, except in red areas. The non-agouti gene does not affect phaeomelanin, the red pigment, so red cats always show their tabby pattern.
The red gene "overrides" the solid gene, making the tabby pattern visible again. (And on other solid colors, you can sometimes notice the underlying stripes, especially in strong light.) Solid red cats at cat shows may or may not be genetically solid--they are (generally longhairs) bred for the "blurring" of the tabby pattern, producing a cat that doesn't have dramatic markings.
Solid Tabby ----- ----- black brown tabby blue blue tabby red red tabby cream cream tabby chocolate chocolate tabby cinnamon cinnamon tabby fawn fawn tabby
The colors a calico will produce depend on the color of the sire. But at minimum, she can produce red and non-red sons, and patched tabby/tortoiseshell/calico daughters, as well as non-red daughters. Whether she will produce tabbies or not depends on the genetic makeup of the sire. And *any* of the kittens could have white markings, or not.
Basic cat colors:
Color Dilute form ----- ----------- black blue (a grey color) chocolate lilac (a pale pinkish-grey) (chocolate is a recessive gene which changes black to brown) cinnamon fawn (a very pale pinkish-tan) (a light reddish brown, found mostly in Siamese and Abyssinians) red cream (ranges from yellowish to tannish or buff) (red and cream are sex-linked, on the X gene, and mask the previous colors. Actually, there's a separate shade of red/cream to match each of the previous colors, but it's hard to tell them apart, unless you're dealing with a tortoiseshell or patched tabby, which has the non-red areas to give you a hint.) white (Here we refer to the dominant form, which is masking over the previous colors. It has no dilution.)
Everything else is a modifier!
Modifier Dominant/Recessive -------- ------------------ white spotting (paws, etc) dominant polydactyly (extra toes) dominant manx (taillessness) dominant silver (inhibits hair color at roots) dominant white locketing (small spots on chest and/or groin) recessive dilution (black->blue) recessive chocolate dilution recessive cinnamon dilution recessive bobtail (partial taillessness) recessive solid (no tabby markings) recessive long hair recessive
Some genes are incompletely dominant to each other, and are part of a series. For example, the siamese/burmese genes, from most to least colored:
Burmese/Siamese/blue-eyed white/pink-eyed white (albino)
The coloring of the Burmese and the points of the Siamese is temperature sensitive. The cooler extremities of the Siamese are darker; a Burmese that has had a fever may grow in lighter fur for a while! Such changes are usually temporary, but may take some time to grow out.
All cats (even those homozygous for solid) have a tabby pattern. There are different tabby patterns, from most to least dominant:
Mackerel/Classic/Ticked. The spotted tabby pattern is thought to be a var`qiant of the Mackerel pattern, not genetically distinct, but the jury is not yet in.
Smokes and Chinchillas. This is the combination of the expression of the silver gene (a dominant), and the gene for solid color (a recessive). Other modifiers account for whether the cat is a referred to as a smoke, a shaded, or a chinchilla. From most to least colored: a "smoke" has white roots, a "shaded" has about half and half white and color along the length of the hair, and a "chinchilla" has color only on the very tips of the hair. If the cat is a tabby instead of a solid color, that is a silver tabby. And if the base color is not black, that would be added to the name as well: blue-cream smoke, red silver tabby, etc.