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Tortoiseshell cat

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Tortoiseshell describes a coat coloring

Animal colouration

Animal colouration has been a topic of interest and research in biology for well over a century. Colours may be cryptic Animal colouration has been a topic of interest and research in biology for well over a century. Colours may be cryptic Animal colouration has been a topic of interest and...

found almost exclusively in female cat

Cat

The cat , also known as the domestic cat or housecat to distinguish it from other felines and felids, is a small carnivorous mammal that is valued by humans for its companionship and its ability to hunt vermin and household pests...

s. Cats of this color are mottled, with patches of orange or cream and chocolate, black or blue. They are sometimes called torties for short.

The term "tortoiseshell" is typically reserved for cats with brindle

Brindle

Brindle is a coat coloring pattern in animals, particularly dogs, cats, cattle, crested geckos and, rarely, horses. It is sometimes described as "tiger striped", although the brindle pattern is more subtle than that of a tiger's coat...

d coats that have relatively few or no white markings.

Those that are largely white with red and brown patches (rather than a brindled aspect) are described as tortoiseshell-and-white (in the United Kingdom

United Kingdom

The United Kingdom of Great Britain and Northern Ireland is a sovereign state located off the northwestern coast of continental Europe. It is an island country, spanning an archipelago including Great Britain, the northeastern part of Ireland, and many small islands...

) or calico (in Canada and the United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

). Tortoiseshells and calicos are not specific breeds of cat. The tortoiseshell markings appear in many different breeds. This pattern is especially preferred in the Japanese Bobtail breed.

Patterns

Tortoiseshell cats have coats with patches of red, brown or black, chocolate, cream, or cinnamon. The size of the patches can vary from a fine speckled pattern to large areas of color. Typically, the more white a cat has, the more solid the patches of color. Dilution genes may modify the coloring, lightening the fur to a mix of cream and blue, lilac or fawn. The markings on tortoiseshell cats are usually asymmetrical. Occasionally tabby

Tabby cat

The tabby cat has a distinctive coat that features stripes, dots, or swirling patterns, usually together with an "M" mark on its forehead. Tabbies are sometimes erroneously assumed to be a breed of cat. In fact, the tabby pattern is found in many breeds of cat, as well as among the general...

patterns of eumelanistic and pheomelanistic colors are also seen (these are often then called "tortie-tabby", "torbie" or "caliby"). Tortoiseshell also can be expressed in the point

Point (coat color)

Point coloration refers to animal coat coloration with a pale body and relatively darker extremities, i.e. the face, ears, feet, tail, and scrotum...

pattern.

Genetics

Tortoiseshell and calico coats result from an interaction between genetic and developmental factors. The primary gene for coat color (C) is located on the X Chromosome

X chromosome

The X chromosome is one of the two sex-determining chromosomes in many animal species, including mammals . It is a part of the XY sex-determination system and X0 sex-determination system...

and has two co-dominant alleles, Orange (X^O) and Black (X^B), that produce orange phaeomelanin and black eumelanin pigments, respectively. The cells of female cats, which like other mammalian females have two X Chromosome

X chromosome

The X chromosome is one of the two sex-determining chromosomes in many animal species, including mammals . It is a part of the XY sex-determination system and X0 sex-determination system...

(XX), undergo the phenomenon of X-inactivation

X-inactivation

X-inactivation is a process by which one of the two copies of the X chromosome present in female mammals is inactivated. The inactive X chromosome is silenced by packaging into transcriptionally inactive heterochromatin...

, in which one or the other of the X-chromosomes is turned off at random in each cell in very early development. The inactivated X becomes a Barr body

Barr body

In those species in which sex is determined by the presence of the Y or W chromosome rather than the diploidy of the X or Z, a Barr body is the inactive X chromosome in a female cell, or the inactive Z in a male , rendered inactive in a process called Lyonization...

. Cells in which the chromosome carrying the Orange (X^O) allele is inactivated express the alternative Black (X^B) allele. Cells in which the Black (X^B) allele is inactivated express the Orange (X^O) allele. Pigment genes are expressed in melanocytes that migrate to the skin surface later in development. In bi-coloured tortoiseshell cats, the melanocytes arrive relatively early, and the two cell types become intermingled, producing the characteristic brindled appearance consisting of an intimate mixture of orange and black cells, with occasional small diffuse spots of orange and black.

In tri-coloured calico cats, a second gene interacts developmentally with the coat colour gene. This spotting gene

Cat coat genetics

The genetics of cat coat coloration, pattern, length, and texture is a complex subject, and many different genes are involved.- Genes involved in albinism, dominant white, and white spotting :...

produces white, unpigmented patches by delaying the migration of the melanocytes to the skin surface. There are a number of alleles of this gene that produce greater or lesser delays. The amount of white is artificially divided into mitted, bicolor
Bicolor cat
A bicolor cat has white fur combined with fur of some other color, for example black or tabby. There are various patterns of bicolor cat. These range from Van pattern through to solid color with a throat locket...

, harlequin, and van
Turkish Van
The Turkish Van is a recognized cat breed that was created of the cats native to the alpine Lake Van region in Eastern Anatolia of modern Turkey and are named in Turkish Van Kedisi , in Armenian vana katu , , and in Kurdish "pishika Vane"...

, going from almost no white to almost completely white. In the extreme case, no melanocytes make it to the skin and the cat is entirely white (but not an albino). In intermediate cases, melanocyte

Melanocyte

Melanocytes are cells located in the bottom layer of the skin's epidermis, the middle layer of the eye , the inner ear, meninges, bones and heart that produce melanin which is a pigment.-Melanogenesis:...

migration is slowed, so that the pigment cells arrive late in development and have less time to intermingle. Observation of tri-colour cats will show that, with a little white color, the orange and black patches become more defined, and with still more white, the patches become completely distinct. Each patch represents a clone of cells derived from one original cell in the early embryo.

Male cats, like other mammalian males, have only a single X chromosome (XY) that does not undergo X-inactivation: coat color is determined by which allele is present on the X, and they will be either entirely black or orange. Very rarely (approximately 1 in 3,000) a male tortoiseshell or calico is born. These animals typically have an extra X chromosome (XXY), a condition known in humans as Klinefelter syndrome, and undergo an inactivation process like that in females. As in humans, these cats are almost always sterile because of the imbalance in sex chromosomes. Some male calico or tortoiseshell cats may be chimeras

Chimera (genetics)

Typically seen in non-human zoology , a chimera is an animal that has two or more different populations of genetically distinct cells that originated in different zygotes; if the different cells emerged from the same zygote, it is called a mosaicism.Chimeras are formed from four parent cells...

, which result from the fusion in early development of two embryos with different color genotypes. Others are mosaics

Mosaic (genetics)

In genetic medicine, a mosaic or mosaicism denotes the presence of two populations of cells with different genotypes in one individual who has developed from a single fertilized egg...

, in which the XXY condition arises after conception and the cat is a mixture of cells with different numbers of X chromosomes.

Folklore

Cats of this coloration are believed to bring good luck

Luck

Luck is a belief in good or bad fortune in life caused by accident or chancewhich happens beyond a person's control.Luck is significant in everyday life,as well as Morality, Epistemology, Business and other endeavors....

in the folklore of many cultures. In the United States