Date: September 2004
Everyone's skin contain about the same number of
melanocytes even though people come in many different colors. How is this
That probably means that the AMOUNT of melanin in each cell is different.
It is genetically programmed how much melanin a cell will produce. Also, the
production of melanin is through a biosynthetic pathway that has multiple
steps. If any enzymes are mutated in the pathway it doesn;t go to completion
and the product that is produced in the end will be different depending on
where the stop occurred. This also has bearing on the color that is produced.
People whose pathway stops right at the beginning can't make color at all even
if all the other enzymes are fine. These people have albinism.
A large number of gene pairs affect the amount of melanin produced by one's
melanocytes. Dark skinned individuals inherited a large number of genes that
turn on melanin production be their melanocytes. Also,of course, the amount of
sun (UV light) exposure affects the amount of melanin synthesized.
Ron Baker, Ph.D.
I'm not certain it's strictly true that everyone's skin contains about the same number
of melanocytes, but either way, the most important determinant of skin coloration is
melanin production, not melanocyte number. Although the melanin pigment is produced
by melanocytes, melanin production is a "regulated" process, meaning that it can be
increased or decreased. The best example of this is the darkening of light skin by
exposure to UV light, or tanning, which is caused by an increase in melanin
production within the existing melanocytes. The melanocytes of darker-skinned
individuals are just genetically programmed to constantly produce higher levels
of melanin, even without exposure to UV light.
Thanks for the good question,
Jeff Buzby, Ph.D.
CHOC Research Institute
Div. of Educational Programs
Argonne National Laboratory
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Update: June 2012