Թեմա - Heterochromia
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4. Waardenburg syndrome. Genetics Home Reference. October 2012; http: //ghr.nlm.nih.gov/condition/waardenburg-syndrome.
In anatomy, heterochromia is a difference in coloration, usually of the iris but also of hair or skin. Heterochromia is a result of the relative excess or lack of melanin (a pigment). It can be inherited, or caused by genetic mosaicism, chimerism, disease and injury.
Heterochromia of the eye (heterochromia iridis or heterochromia iridum) can be of three types: complete heterochromia (one iris is a different color from the other); congenital heterochromia (heterochromia that is congenital is usually inherited as an autosomal dominant trait) and sectoral heterochromia (in sectoral heterochromia, the iris contains two completely different colors in the same area. Sectoral heterochromia looks like an irregular spot that is a different color than the eye color and does not form a complete ring around the pupil like central heterochromia).
Central heterochromia is an eye condition where there are two colors in the same iris; the central (pupillary) zone of the iris is a different color than the mid-peripheral (ciliary) zone, with the true iris color being the outer color.
Heterochromia is most prevalent in cats and dogs. Sectoral heterochromia is rare in humans; only about 1% of the population has it.
Eye color is a manifestation of the pigment that is present in the iris. Brown eyes are rich in melanin deposits, and blue eyes indicate a lack of melanin. The melanocytes of the iris rest in a richly innervated psuedosyncytium, which is necessary to maintain eye color. Two genes control eye color: EYCL3, found on chromosome 15, which codes for brown/blue eye color (BEY), and EYCL1, found on chromosome 19, which codes for green/blue eye color (GEY). Although previously believed to be inherited in simple Mendelian fashion, eye color has proved to be a polygenic trait. Precisely how these genes interact to provide the full constellation of colors, such as hazel and gray, is as yet unknown. Furthermore, other genes may determine the pattern and placement of pigment in the iris, thereby accounting for solid brown as opposed to rays of color.