1. Skin Color Three pigments: – Melanin – Carotene – Hemoglobin

2. 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

3. 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

4. Acquired vs Inherited

5. BACK TO NORMALCY

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

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

10. Melanocytes All humans have the same relative amount

11. Fraternal Twins

12. Quantitative variation A trait varies continuously along a range of values

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

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

15. One gene? Or several? Recall mendelian genetics…

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

17. How do you set up the Punnett square?

18. 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.

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

20. Freckles and Moles Local accumulations of melanin

21. vitiligo Loss of melanocytes Uneven dispersal of melanin

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