|
Dominant white is a group of genetically related coat color conditions in the horse, best known for producing an all-white coat, but also for producing some forms of white spotting and white markings. Dominant white horses are born with unpigmented pink skin and white hair with dark eyes, although the amount of white hair or spotting can vary depending on which genetic mutation is involved. Dominant white is a rare condition, and under normal conditions, at least one parent must be dominant white to produce dominant white offspring. However, most of the currently-known alleles of dominant white can be linked to a documented spontaneous mutation in a single ancestor. Dominant white can occur in any breed, and has been studied in many different breeds. Two color breeds, the American White Horse and Camarillo White Horse are characterized by their dominant white coats. There are many different forms of dominant white; in genetics, they are labeled ''W1'' through ''W20''. All known dominant white coat colors are associated with the ''KIT'' gene. As the name suggests, these known white coats are inherited dominantly, meaning that a horse only needs one copy of a ''W'' allele to have the white or white spotted coat. Dominant white is genetically distinct from Sabino and both genetically and visually distinct from gray and cremello. Dominant white is not the same as lethal white syndrome, nor are dominant white horses "albinos". Albinism has never been documented in horses. Some forms of dominant white are thought to result in nonviable embryos when a zygote has two ''W'' alleles (is homozygous). However, this has not been verified for all dominant white genetic variations. ==Identification== Dominant white horses are born with pink skin and a white coat, which they retain throughout their lives. Although the term "dominant white" is typically associated with a pure white coat, such horses may be all-white, near-white, partially white, or exhibit an irregular spotting pattern similar to that of sabino horses. The amount of white hair depends on which mutation of ''W'' is involved.〔 Non-white areas of skin and hair are most commonly seen along the dorsal midline of the horse, known as the topline, and are especially common in the mane and on the ears.〔 They may also have interspersed specks or spots of non-white skin and hair. In addition, the hooves are most often white, but may have striping if there is pigmented skin on the coronary band just above the hoof. In some cases, foals born with residual non-white hair may lose some or all of this pigment with age, without the help of the gray factor. Dominant white spotting does not affect eye color, and most dominant white horses have brown eyes. The pink skin is devoid of pigment cells (melanocytes), and appears pink from the underlying network of capillaries. White hair is rooted in unpigmented pink skin. There are many other genetic factors that produce white, near-white, and off-white coat colors in horses, some of which are visually very similar to dominant white. 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「Dominant white」の詳細全文を読む スポンサード リンク
|