Transcript The Genetics of

;
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
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Kian
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Dark skin, brown hair, brown eyes
Remee
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Pale skin, blonde hair, blue eyes
Genes
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Both have white grandmothers & black
grandfathers
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One in a million combination of their
parents’ genes
Mixed twins becoming more frequent
http://www.youtube.com/watch?v=e5ODsf_TEk
Research
Question:
What genetic & environmental factors
contribute to phenotypic color variation?
MC1R Gene
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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
MC1R 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 MC1R gene located?
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the MC1R 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
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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
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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?
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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
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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
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It’s a complex trait, so multiple genes attribute to skin color
MC1R gene
research on zebrafish helped scientists determine skin color gene
o SLC24A5 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
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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
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Use parent’s genotype
Melanin production does not occur at birth
True eye color determined at 3 years old
Albino
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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
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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/6a00d83451a37369e2011570c34344970c-pi
http://upload.wikimedia.org/wikipedia/commons/6/6a/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/MC1R
http://www.hair-science.com/_int/_en/topic/topic_sousrub.aspx?tc=ROOT-HAIRSCIENCE%5EAMAZINGLY-NATURAL%5ECOLOR-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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