In the extreme case, no melanocytes make it to the skin and the cat is entirely white (but not an albino). The amount of white is artificially divided into mitted, bicolor, harlequin, and van, going from almost no white to almost completely white. There are a number of alleles of this gene that produce greater or lesser delays. This spotting gene produces white, unpigmented patches by delaying the migration of the melanocytes to the skin surface. In tri-colored calico cats, a separate gene interacts developmentally with the coat color gene. In bi-colored tortoiseshell cats, the melanocytes arrive relatively early, and the two cell types become intermingled this produces the characteristic brindled appearance consisting of an intimate mixture of orange and black cells, with occasional small diffuse spots of orange and black. Pigment genes are expressed in melanocytes that migrate to the skin surface later in development. Cells in which the non-orange (o) allele is inactivated express the orange (O) allele. Cells in which the chromosome carrying the orange (O) allele is inactivated express the alternative non-orange (o) allele, determined by the (B) gene. įemale cats are homogametic (XX) and undergo the phenomenon of X-inactivation, in which one of the X chromosomes is turned off at random in each cell in very early embryonic development. Therefore, a tortoiseshell cat may be a chocolate tortoiseshell or a blue/cream tortoiseshell or the like, based on the alleles for the (B) and (D) genes. Various terms are used for specific colors, for example, gray is also called blue, orange is also called ginger. Orange becomes cream, black becomes gray, etc. The (B) and (O) genes can be further modified by a recessive dilute gene (dd) which softens the colors. Tortoiseshell and calico cats are labeled X OX o, indicating O-gene heterozygosity. Typically, the alleles are notated as an uppercase O for orange, or a lowercase o for not-orange. The primary gene for coat color (B), for the colors brown, chocolate, cinnamon, etc., can be masked by the co-dominant gene for the orange color (O), which is on the X chromosome and has two alleles: orange (X O) and not-orange (X o) that produce orange phaeomelanin and black eumelanin pigments, respectively. Tortoiseshell and calico coats result from an interaction between genetic and developmental factors. In the course of his studies he discovered that the rare tortoiseshell male is often sterile. Leonard Doncaster was the first to prove that tortoiseshell is the female heterozygote of orange and black, the corresponding male being orange. Tortoiseshell coloring can also be expressed in the point pattern, referred to as a tortie point. Not uncommonly there will be a "split face" pattern with black on one side of the face and orange on the other, with a dividing line running down the bridge of the nose. These patched tabbies are often called a tortie-tabby, a torbie or, with large white areas, a caliby. Occasionally tabby patterns of black and brown (eumelanistic) and red (phaeomelanistic) colors are also seen. 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. Typically, the more white a cat has, the more solid the patches of color. The size of the patches can vary from a fine speckled pattern to large areas of color. Tortoiseshell cats have particolored coats with patches of various shades of red, grey, and black, and sometimes white. Patterns Cat with a blue ("dilute") tortoiseshell coat A tortoiseshell with characteristic "split-face" pattern This pattern is especially preferred in the Japanese Bobtail breed, and exists in the Cornish Rex group. Tortoiseshell markings appear in many different breeds, as well as in non-purebred domestic cats. Those that are predominantly white with tortoiseshell patches are described as tricolor, tortoiseshell-and-white, or calico (in Canada and the United States). "Tortoiseshell" is typically reserved for multicolored cats with relatively small or no white markings. Tortoiseshell cats with the tabby pattern as one of their colors are sometimes referred to as torbies or torbie cats. The colors are often described as red and black, but the "red" patches can instead be orange, yellow, or cream, and the "black" can instead be chocolate, gray, tabby, or blue. Tortoiseshell cats, or torties, combine two colors other than white, either closely mixed or in larger patches. Male tortoiseshells are rare and are usually sterile. Like tortoiseshell-and-white or calico cats, tortoiseshell cats are almost exclusively female. Tortoiseshell is a cat coat coloring named for its similarity to tortoiseshell pattern.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |