The Genetics of Phenotypic Pigmentation What factors contribute

; The Genetics of Phenotypic Pigmentation ;

What factors contribute to phenotypic color variation? A. Environment B. Genetics C. Neither D. Both E. I don’t know

Million-to-One Black & White Twins • • • Kian o Dark skin, brown hair, brown eyes Remee o Pale skin, blonde hair, blue eyes Genes o Both have white grandmothers & black grandfathers o One in a million combination of their parents’ genes • Mixed twins becoming more frequent

http: //www. youtube. com/watch? v=e 5 ODsf_TEk

Research Question: What genetic & environmental factors contribute to phenotypic color variation?

MC 1 R Gene • • Melanin is the substance that gives skin, hair, and eyes their color o Two main types of melanin: § eumelanin - brown or black hair and dark skin that tans easily § pheomelanin - red or blonde hair, freckles, and light skin MC 1 R gene: makes protein called melanocortin 1 receptor which plays an important role in pigmentation o Located on surface of “melanocytes” o melanocortin 1 receptor controls which type of melanin is produced § Activation → production of eumelanin § Inactivation → production of pheomelanin

Where is the MC 1 R gene located? • the MC 1 R gene is located from base pair 89, 917, 878 to base pair 89, 920, 976 on chromosome 16.

Which type of melanin contributes to Scandinavian blonde hair? A. Eumelanin B. Pheomelanin C. Neither D. Both

Hair color • • • All colors of hair can lose their pigmentation over time and become the gray and white hair associated with older age Scandinavian blond hair is also mainly formed from eumelanin Immense range possible in the mixtures of the two pigments Distribution of melanin is determined by genetics These ranges depend on type as well as quantity

• • Cells responsible for hair color (melanocytes) are large star-shaped cells, with branches called dendrites Found mainly at the bottom of the hair follicle, they manufacture melanin in the form of small grains of colored pigment After melanin is formed, the dendrites lengthen and inject the pigments into the keratinocytes of the hair shaft as it’s being formed Melanin in hair color is proportional to intensity

How Have Different Skin Colors Developed? • • Humans lost hair in order to keep cool Loss of hair associated with increase of UV sunlight exposure Melanin absorbs UV radiation thus decreasing risk for UV related cancer Skin color evolved by natural selection from sunlight exposure

Effects of UV Rays • • • Darker skin means that Vitamin B Folate will not be destroyed from UV rays Folate is necessary for healthy reproduction, DNA Synthesis, and Rapid Cell Proliferation UV Rays facilitate Vitamin D production Darker skin means less UV Rays penetrate and thus more rays are needed to produce vitamin D Diets rich in Vitamin D maintain dark skin colors Excess of UV rays causes premature skin aging and wrinkling

Not just Skin Deep • • • It’s a complex trait, so multiple genes attribute to skin color MC 1 R gene research on zebrafish helped scientists determine skin color gene o SLC 24 A 5 gene in humans Recent Migration Effects Skin Cancer Race is a social construct

Which one of the following is false about UV Rays? A. An excess of UV Rays can cause skin cancer B. UV rays over a long period of time darken skin C. UV rays contribute to the production of Vitamin D D. UV Rays cause a reduction of Vitamin B Folate which ensures healthy human birth E. UV rays cause premature skin aging and wrinkling

Eye Color How Children Inherit Eye Color • • • Different eye colors produced from different amounts and patterns of pigment in iris DNA from parents will determine the child’s eye phenotypic color Melanin is substance that produces the eye colors The more melanin means the darker the eye color The genes tell the enzymes how much melanin to deposit Predicting Children’s Eye Color • • • Use parent’s genotype Melanin production does not occur at birth True eye color determined at 3 years old Albino • • Have no pigment in either layer of the iris Iris appears red because of the reflection of blood vessels in the back of the eye 2 Different Eye Colors • • • Called Heterochromia Caused by a difference in the early stages of development of the iris Caused by diseases in the eye or certain types of medicine

Why do albino people appear to have red eyes? A. The large amount of melanin causes eyes to turn red B. The reflection of blood vessels in the back of the eye are shown through the iris C. Melanin mixes with blood in the eye D. Red eyes are the result of the blue and green gene shading

Photo Sources http: //www. wnyc. org/i/1200/627/80/photologue/photos/Race_FINAL_shea_walsh_web. jpg http: //peterlumpkins. typepad. com/. a/6 a 00 d 83451 a 37369 e 2011570 c 34344970 c-pi http: //upload. wikimedia. org/wikipedia/commons/6/6 a/Unlabeled_Renatto_Luschan_Skin_color _map. svg

Reference List http: //www. dailymail. co. uk/news/article-2123050/Look-The-black-white-twins-turn-seven. html http: //ghr. nlm. nih. gov/gene/MC 1 R http: //www. hair-science. com/_int/_en/topic_sousrub. aspx? tc=ROOT-HAIRSCIENCE%5 EAMAZINGLY-NATURAL%5 ECOLOR-PALETTE&cur=COLOR-PALETTE http: //humanorigins. si. edu/evidence/genetics/skin-color/modern-human-diversity-skin-color http: //www. ishrs. org/articles/hair-color. htm http: //news. psu. edu/story/299166/2014/01/02/research/studies-skin-color-gene-across-globalpopulations-reveal-shared

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