Skin Color Three pigments: – Melanin – Carotene – Hemoglobin

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

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

Acquired vs Inherited

BACK TO NORMALCY

Melanocytes Produce melanin (cluster = melanosome) Located in the stratum germinativum

How did differences in skin color among races evolve? – Protection from UV light vs vitamin D?

Melanocytes All humans have the same relative amount

Fraternal Twins

Quantitative variation A trait varies continuously along a range of values

 So how do we get different skin colors?  How is skin color inherited?

Usually as the result of the interaction with the environment and several different genes

One gene? Or several? Recall mendelian genetics…

Multiple Gene Inheritance Polygenic inheritance – Each gene follows dominant/recessive pattern – Combined effects add together

How do you set up the Punnett square?

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.

There are more than 7 skin colors though… – Explanation?

Freckles and Moles Local accumulations of melanin

vitiligo Loss of melanocytes Uneven dispersal of melanin

albinism Melanocytes do not produce melanin Skin = pink, hair = pale/white, irises = unpigmented or poorly