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Equine coat color genetics determine a horse's coat color. There are many different coat colors possible, but all colors are produced by the action of only a few genes. The simplest genetic default color of all domesticated horses can be described as either "red" or "non-red", depending on whether a gene known as the "Extension" gene is present . When no other genes are active, a "red" horse is the color popularly known as a chestnut. Black coat color occurs when the Extension gene is present, but no other genes are acting on coat color.The ''Agouti'' gene can be recognized only in "non-red" horses; it determines whether black color is uniform, creating a black horse, or limited to the extremities of the body, creating a bay horse. Chestnut and black are considered the "base" colors that all remaining coat color genes act upon. Bay (Agouti) is the most common modifier, restricting the black pigment to the points of the horse. There are a number of dilution genes that lighten these colors in a variety of ways, sometimes affecting skin and eyes as well as hair coat, including cream, dun, pearl, champagne and silver dapple. Genes that affect the distribution of white and pigmented coat, skin and eye color create patterns such as roan, pinto, leopard, white, and even white markings. Some of these patterns may be the result of a single gene, others may be influenced by multiple alleles. Finally the gray gene, which acts differently from other coat color genes, slowly lightens any other hair coat color to white over a period of years, without changing skin or eye color.〔Note: For a quick lesson in genetics and heredity, see also 〕 ==Fundamental concepts and terminology== Much of the modern understanding of equine coat color genetics is owed to the work of Dr. Ann T. Bowling of the University of California, Davis and of Dr. Phillip Sponenberg of Virginia Polytechnic Institute. Modern discussions of horse coat color genetics are based on the distinction between "red" and "non-red" coats, a factor determined by a single gene. More detailed discussions of coat color all refer to the differing effects of separate genes on these "base" coat colors.〔"Genetics of Champagne Coloring." ''The Horse'' online edition, accessed May 31, 2007 at http://www.thehorse.com/viewarticle.aspx?ID=9686〕 Coat color alleles affect melanin, the pigment or coloring of the coat. There are two chemically distinct types of melanin: pheomelanin, which is perceived as red to yellow color, and eumelanin, is perceived as brown to black. All coloration genes in mammals affect either the production or distribution of these two chemicals. Alleles affecting melanocytes (pigment cells) do not alter the pigment chemicals themselves but rather by acting on the placement of pigment cells produce distinct patterns of unpigmented pink skin and corresponding white hair.〔Rieder ''et al'' 2001. "These genes can be classified into two main groups: those acting on the melanocyte—its development, differentiation, proliferation, and migration; and those acting directly on pigment synthesis."〕 Heritable characteristics are transmitted, encoded, and used through a substance called DNA, which is stored in almost every cell in an organism. DNA is organized into storage structures called chromosomes. For the most part, chromosomes come in matched sets, one chromosome from each parent. The location of a gene on a chromosome is called its locus. Alternate forms of a gene are called alleles.〔 The terms Alleles and Modifiers are used interchangeably and describe the same concept. An allele identified with a capital letter is a dominant trait, one identified with a lower-case letter is a recessive trait. Because sex cells (sperm and ova) contain only half the usual number of chromosomes, each parent contributes one allele in each gene set to the ensuing offspring. When an individual's gene set contains two copies of the same allele, it is called homozygous for that gene. When it has two different alleles, it is heterozygous. For a recessive trait to be expressed, it must be homozygous, but a dominant trait will be expressed whether it is heterozygous or homozygous. A horse homozygous for a certain allele will always pass it on to its offspring, while a horse that is heterozygous carries two different alleles and can pass on either one. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「equine coat color genetics」の詳細全文を読む スポンサード リンク
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