While a calico cat and a tortoiseshell cat look differently, they are not different breeds. Even though the two types of cats offer different variations, the base colours of the cats are the same. These cats will always exhibit white, a form of red and one other colour, typically black or blue.
The biggest difference between a calico cat and a tortoiseshell cat is the way the colours represent themselves. In a calico cat, the three colours present themselves in solid patches. The three colours exist independent of each other, with white being the typical primary colour. For a tortoiseshell cat, the colours are mixed together so you cannot tell where one begins and the other ends. Therefore, these cats tend to appear darker in colour overall.
Amount of White
In general, a calico cat will have a large portion of one colour of fur on its body. In fact, some people use this distinction to determine the difference between the two kinds of cats. However, a tortoiseshell cat may also have larger patches of one colour. As long as the other two colours on the cat are blended together and not presented in solid patches, the cat is classified as a tortoiseshell. Most tortoiseshell cats also have their dominant-coloured fur blended with the other colours rather than being solid.
Calico and tortoiseshell cats have three different colours of fur on their bodies. However, one of these colours is typically the dominant colour, meaning it appears on a larger portion of the cat's body. For calico cats, the typical dominant colour is white. For some calico cats, up to half of its body may be covered by the dominant colour only. For tortoiseshell cats, the dominant colour is more commonly black. Since their other colours typically blend together with the dominant colour, it can be a little more difficult to pick out the dominant colour of a tortoiseshell cat.
The genetics for a calico cat and a tortoiseshell cat are pretty much the same. The gene for these colour combinations is carried on the female chromosome, which means that most cats who carry these colour markings are female cats. Genetic abnormalities do occur to create male calico and tortoiseshell cats, but these cats are usually infertile because of the abnormality. The dominant colour gene for cats results in an orange cat if both genes are dominant. If both colour genes are recessive, the cat will be another colour. However, if the female cat gets a dominant and a recessive, she will most likely be calico or tortoiseshell.