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| Question | Answer |
| What Gives Skin Its Color... | 1. Melanin - pigmentation for humans 2. Hemoglobin - iron transporting element in your skin |
| Craig Miller's Study | KTLG (Kit Ligand gene) Responsible for dark/light pigmenation 1. Stickelback (light fish) fish have a divergent allele of KTLG 2. Europeans, E. Asians, also have derived alleles at KTLG locus 3. Regulatory regions of KITLG have evidence of strong selection in humans 4. Convergence or conserved mechanism in fish and humans for lighter pigmentation |
| Reflectance | Higher pigmentation = lower reflectance of light Note: People with darker skin closer to equator (more sunlight) & selection of darker skin in northern regions to due snow reflectance |
| What in the Physical Environment is Most Closely Correlated with Skin Color? | UV Radiation Note: higher elevation = more exposure to UV (i.e. in Himalayas) |
| Correlations: Skin color with Average UVR | Inverse Corrleation |
| Reflecatnace Correlation vs. Melanin Correlation | Reflectance: higher pigmentation = lower reflectance (negative correlation) Melanin Content: higher pigmentation = higher UV radiation (positive correlation) |
| Melanin | regulated the amount of sunlight entering the body....its a natural sunscreen |
| UVR | 1. UVA breaks down Folate 2. Folate deficiency slows the production of DNA |
| How does UVR Profoundly Affect Biological Systems? | 1. Damage to DNA 2. Inhibition of photosynthesis in phytoplankton 3. Damage to cell membranes 4. Photolysis of bioactive compounds (Folate, vitamin B12) 5. Catalyzes pre-vitamin D3 synthesis (postitive) |
| Folate and Human Development | Folate is needed for all processes requiring cell division especially in early embryonic stages of development and in the production of sperm |
| Birth Defects due to Folate Deficiency | Spina Bifida - neural tube defects where cysts form on baby's back |
| Genes Influencing Variation in Skin Pigmenation (Part 1) | 1. MC1R (Melancortin 1 receptor locus) - makes a protein that affects the color of skin and hair 2. regulates melanin production, shows little variation in African populations, but exhibits extensive allelic variation in Europe (i.e. these mutations were selected against in African populations and highly selected for in European populations)_ |
| Vitamin D and UVR | You need some UVR to make Vitamind D: Vitamin D is needed to build and maintain strong bones and to maintain a healthy immune system Vitamin D functions as a horomone, tells intestine to absorb calcium |
| Developmental Defects to due Vitamin D Deficiency | Rickets - bones are too soft causing deformation in the legs and pelvis Note: Recent rise of Rickets in 20% of UK Children in all social classes, also prominent in Saudi Arabia |
| Genes Influencing Variation in Skin Pigmenation (Part 2) | KITLG - European and E. Asian populations DCT - Chinese populations MATP, LSC34A5, OCA2, TYRP1 - European populations MC1R - European populations |
| Parallel (Convergent) Evolution for Skin Color | 1. Light skin has evolved several times in our lineage and at least twice in modern humans 2. Light skin of Europe and Asians is an example of convergent evolution |
| Pigment in Neanderthals | Recall: Peninsular Europe (130,000 - 30,000 years ago, cold adapted) 2 Neanderthals were found to have a mutation in the MC1R gene that impairs its function - No modern human has the same mutation Potentially strongly correlated to red hair and freckles |
| Northern Regions and Vitamin D | Due to the lack of sunlight ad Vitamin D, they eat foods high in Vitamin D to survive (we have fossil evidence of people living in Northern regions since 24,000 years ago) |
| The Evolutionary Advantages of Dark Skin | 1. Dark skin acts as a natural sunscreen and protects against breakdown of folate by UVR |
| The Evolutionary Advantages of Light Skin | In geographic regions where UVR level is low, skin with less melanin facilitates the production of Vitamin D |
| SUMMARY | 1. Skin pigmentation is an evolutionary adaptation for regulating penetration of UVR into the skin 2. Skin pigmentation represents a compromise between the demands of protecting the body and making enough Vitamin D 3. Skin Pigmentation can change in response to environmental conditions over thousands of years. 4. Dark and light skins have evolved many times in human history |
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