1. SKIN COLOR

2. melanin - brown-black, and red-yellow pigment
The wide variety of colors in skin is due to three pigments:
melanin - brown-black, and red-yellow pigment
carotene - yellow-orange pigments (from some vegetables)
hemoglobin - red color of oxygenated blood in capillaries
Melanin is made in the skin and
is the primary pigment that determines skin color.

3. There are two types of melanin: eumelanin – black-brown form
pheomelanin – red-yellow form
The more eumelanin in your epidermis,
the darker your skin.
Light skin contains little eumelanin.
Fair skin, freckling, and carrot-red hair is associated with large amounts of pheomelanin and small amounts of eumelanin.

4. There are two types of melanin:
eumelanin – black-brown form
(dark skin, moles, blemishes, birthmarks)
(blonde to dark brown hair)
pheomelanin – red-yellow form
(nipples, lips, freckles, genitalia)
(red hair)

5. What is the function of melanin?
Melanin is a pigment that absorbs UV radiation,
thereby protecting cells from the harmful effects
of UV rays.
UV rays may cause skin cancer and premature aging.
When UV rays penetrate the skin, it helps the human body make vitamin D which functions in absorbing calcium (necessary for strong bones).

6. Exposure to the sun, to UV radiation,
activates your melanocytes to produce
more melanin, resulting in a tan.

7. Skin Color and Natural Selection
Differences in UV radiation have driven selection for dark human skin at the equator and for light human skin at greater latitudes. As people moved to areas farther from the equator with lower UV levels, natural selection favored lighter skin which allowed UV rays to penetrate and produce essential vitamin D. The darker skin of peoples who lived closer to the equator was important in preventing UV damage to cells.

8. Melanocytes are cells that produce melanin.
The melanin is packaged into vesicles
called melanosomes.
Melanosomes travel to and are taken up by keratinocytes.

9. Light-skinned and dark-skinned individuals have
the same number of melanocytes.
But dark-skinned individuals, their melanocytes produce more melanosomes, their melanosomes are larger, and contain more melanin.

10. The characteristic phenotype of fair skin, freckling, and carrot-red hair is associated with large amounts of pheomelanin and small amounts of eumelanin.
For the same body region, light- and dark-skinned individuals have similar numbers of melanocytes (there is considerable variation between different body regions), but pigment-containing organelles, called melanosomes, are larger, more numerous, and more pigmented in dark compared to intermediate compared to light skin, corresponding to individuals whose recent ancestors were from Africa, Asia, or Europe, respectively.
Of equal importance to what happens inside melanocytes is what happens outside. Each pigment cell actively transfers its melanosomes to about 40 basal keratinocytes; ultimately, skin reflectance is determined by the amount and distribution of pigment granules within keratinocytes rather than melanocytes. In general, melanosomes of African skin are larger and dispersed more widely than in Asian or European skin (Figure 1). Remarkably, keratinocytes from dark skin cocultured with melanocytes from light skin give rise to a melanosome distribution pattern characteristic of dark skin, and vice versa (Minwalla et al. 2001). Thus, at least one component of skin color variation represents a gene or genes whose expression and action affect the pigment cell environment rather than the pigment cell itself