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Chapter 5 - Exam Review Notes

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Ann Herring

Chapter 5Exam Notes Variation in Skin Colour Polygenetic Trait Trait controlled by more than one geneDetermined by amount of melanin hemoglobin carotene in the skin Hemoglobincarried oxygen gives reddish tinge Melaninabsorbs UV rays prevents damage to DNA Carotenefrom food plants yellowish castSkin StructureMelanin produced by melanocytes absorbs UV lightprotects from sunburnTanningburning temp increase melanin productionDarker skingreater melanocyte activity NOT more melanocytesDarker skincloser to equator lighter skinfarther away from equatorWhat are Clines Cline Gradual change in the frequency of a trait or allele in populations dispersed over geographical spaceVariation explained by evolutionCloser to equator more UV darker skin father away from equator less UV lighter skinThe Vitamin D HypothesisVitamin D essential for normal bone growth and mineralizationLack of vitamin D can cause rickets in childrenbones become soft Lead to reduced reproductive fitness especially in femalesVitamin D synthesized when exposed to UV radiationDarker skin would inhibit synthesis of Vit DLighter skinin areas with less UV radiation sufficient vitamin D Sufficient vitamin D Selection for less melanin where UV is weakDarker skinprotects against production of too much vitamin D Protects against production of too much vitamin D Selection for more melanin where UV is strongThe Folate Hypothesis Photolysis Chemical decomposition caused by visible lightUV light causes photolysis of folate Vitamin Bneeded to synthesis and repair of DNARisk of folate deficiency in areas of high UV radiationLink between folate deficiency and neural tube defects in infants spina bifidaDarker skin protects against folate photolysis Increased reproductive success in early humansEXCEPTIONSDiet high in vitamin DShort period of occupation in the North 5000 yrs 1
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