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Modern Human Variation

Modern Human Variation - I a Biology i Pigmentmelanin ii...

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Modern Human Variation   I. Skin Pigmentation and Solar Radiation a. Biology i. Pigment melanin ii. Epidermis (outer layer of skin - cells of epidermis) 1. Keratinocytes - cells that synthesize keratin 2. Melanocytes - cells that synthesize melanin.  The melanin is  coalesced into packets called melanosomes.  The melanosomes  are transferred to the keratinocytes a. Albinism - genetic inability to synthesize an enzyme in  the production of melanin b. Tyrosine --> DOPA --> melanin b. Comparisons of Populations i. Genetic similarity among populations 1. All populations have the same number of melanocytes in  corresponding areas of the body ii. Genetic differences among populations 1. Difference in size of melanosomes - heavily melanized  populations have larger melanosomes than lightly pigmented  populations 2. Rate of production of melanosomes - heavily melanized  populations have more melanosomes than lightly pigmented  populations 3. Degree of dispersion of melanosomes within the keratinocyte - in  heavily melanized populations, the melanosomes are more  dispersed within the keratinocyte c. Reversible Acclimatization: Tanning d. Hypotheses to explain genetic differences among populations i. Ultraviolet radiation promotes skin cancer.  Melanin functions to absorb 
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