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Published bySharlene Hawkins Modified over 9 years ago
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Skin Color Three pigments: – Melanin – Carotene – Hemoglobin
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Why do veins look blue? Blood lower than oxygen = brownish in color Veins are closer to the surface than arteries Walls of veins are thinner Light-scattering effect of epidermis: blue light is the only light that makes it to veins
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Blue people of Kentucky Methemoglobinemia – Variation in hemoglobin (instead of Fe2+, it has Fe3+) – Decreased ability to bind oxygen – Arterial blood = brown instead of red – Skin appears blue-ish
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Acquired vs Inherited
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BACK TO NORMALCY
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Melanocytes Produce melanin (cluster = melanosome) Located in the stratum germinativum
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How did differences in skin color among races evolve? – Protection from UV light vs vitamin D?
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Melanocytes All humans have the same relative amount
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Fraternal Twins
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Quantitative variation A trait varies continuously along a range of values
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So how do we get different skin colors? How is skin color inherited?
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Usually as the result of the interaction with the environment and several different genes
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One gene? Or several? Recall mendelian genetics…
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Multiple Gene Inheritance Polygenic inheritance – Each gene follows dominant/recessive pattern – Combined effects add together
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How do you set up the Punnett square?
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modeling Under this model, are the statements true or falsE? – When one parent is white (zero dominant alleles), the progeny can be no darker than the other parent. – When one parent is light (one dominant allele), the progeny can be no darker than the other parent.
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There are more than 7 skin colors though… – Explanation?
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Freckles and Moles Local accumulations of melanin
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vitiligo Loss of melanocytes Uneven dispersal of melanin
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albinism Melanocytes do not produce melanin Skin = pink, hair = pale/white, irises = unpigmented or poorly
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