Skin Color Three pigments: – Melanin – Carotene – Hemoglobin.
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Transcript of Skin Color Three pigments: – Melanin – Carotene – Hemoglobin.
![Page 1: Skin Color Three pigments: – Melanin – Carotene – Hemoglobin.](https://reader033.fdocuments.in/reader033/viewer/2022061317/56649efd5503460f94c107f3/html5/thumbnails/1.jpg)
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