<P> Since the action spectrum of sunburn and melanogenesis are virtually identical, they are assumed to be induced by the same mechanism . The agreement of the action spectrum with the absorption spectrum of DNA points towards the formation of cyclobutane pyrimidine dimers (CPDs) - direct DNA damage . </P> <P> Typically, between 1000 and 2000 melanocytes are found per square millimeter of skin or approximately 5% to 10% of the cells in the basal layer of epidermis . Although their size can vary, melanocytes are typically 7 μm in length . </P> <P> The difference in skin color between lightly and darkly pigmented individuals is due not to the number (quantity) of melanocytes in their skin, but to the melanocytes' level of activity (quantity and relative amounts of eumelanin and pheomelanin). This process is under hormonal control, including the MSH and ACTH peptides that are produced from the precursor proopiomelanocortin . </P> <P> People with oculocutaneous albinism typically have a very low level of melanin production . Albinism is often but not always related to the TYR gene coding the tyrosinase enzyme . Tyrosinase is required for melanocytes to produce melanin from the amino acid tyrosine . Albinism may be caused by a number of other genes as well, like OCA2, SLC45A2, TYRP1, and HPS1 to name some . In all, already 17 types of oculocutaneous albinism have been recognized . Each gene is related to different protein having a role in pigment production . </P>

Where are keratinocytes and melanocytes found in the skin