๐ ็ธฝ็ฎ้ ๏ฝ ๐ ่ฑๆๅๆ๏ผๆฌ็ฏ๏ผ ๏ฝ ๐ ๅฎๆด็ฟป่ญฏ ๏ฝ โญ ็ฒพ่ฏ็ญ่จ
A locus
A locus
The switch from eu- to pheomelanogenesis is regulated by a number of genes, namely pro-opiomelanocortin-alpha (Pomc/ฮฑ-Msh), melanocortin 1 receptor (Mc1r), nonagouti (A), mahogunin, ring finger 1 (Mgrn1), and attractin (Atrn). Eumelanin synthesis is promoted when POMC binds to the MC1R receptor, which in turn leads to the activation of the cyclic
The agouti locus is located on chromosome 2 of the mouse genome and is associated with the nonagouti (a) gene. Agouti acts in the hair follicles, primarily affecting the relative amount and distribution of yellow pigment (pheomelanin) and black/brown pigment (eumelanin) in hair. Agouti mice have banded hairs whereby a band of black melanin resides at the top of the hair followed by yellow melanin in the middle and ending with black pigment near the end of the hair shaft. Currently, there are nearly 150 known variations in the agouti locus conferring a range of coat colors and pleiotropic phenotypes (http://www.informatics.jax.org; August 2016).
The human equivalent of the nonagouti (a) gene in mice is the agouti signaling protein (ASIP) gene located at 20q11.22. Several studies using small cohorts have found single nucleotide polymorphisms (SNPs) in and around the ASIP gene that show a weak correlation between ASIP and human skin and hair pigmentation.13,14 In addition, a melanoma risk locus was identified by three separate studies residing near ASIP. This locus increases the risk of early onset cutaneous melanoma and basal cell carcinoma.15
1904 Animal models of skin disease