Evolutionary Genetics Selection and Skin Pigmentation
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Course
MCB3023S (MCB3023S)
Institution
University Of Cape Town (UCT)
In these notes the following is covered:
• An introduction to pigmentation
• The genetic variants linked to pigmentation
• A pigmentation gene conserved across species
• What was the skin color of Neanderthals?
,
,INTRODUCTION TO SKIN PIGMENTATION
G- WAS looking at responsible for
genes
and colour
skin colour eye
1
, Read paper Sulem et al paper
Watch the Nina Jablonski video
• Try to do this ASAP: this will allow to
engage better with the next few lectures
, Adaptation & Positive Selection in Human Populations:
not unique in
genes
Near equator 1- tropics -_
more
pigment Skin Pigmentation
_
-
humans
•
higher /
northern latitudes __ less pigment
• Skin is darker (more pigmented) for people living at the tropics and lighter
(less pigmented) skin in people from colder climates
• When early humans moved into hot, open environments, adaptations to keep
cool were favoured e.g. increase in number of sweat glands & decrease in
body hair
• “Hairless” skin is exposed to very strong sun near the equator results in
damage sunburn damage DNA
-
,
• Solution of a permanently dark skin was to protect against the sun’s more
damaging rays Lnatura / sun block -
3
,• Human pigmentation is the most visible, variable and
differentiating human trait
• Pigmentation is the result of melanin in skin, eyes and hair
• Variation in pigmentation is
determined by:
• amount
• type
• distribution of melanin within
melanocytes
[
specialized
• The number of melanocytes in a cell
L kind of
does not usually vary pigment
produced 4
,Variation in pigmentation is an adaptive trait in humans
( based on and latitude
geography
The strong correlation between skin colour and place of origin this
suggests that pigmentation is environmentally induced adaptation
UVA
radiation
• Latitude* is environmental factor that strongly correlates with the
intensity & duration of solar radiation (especially UVA radiation)
• Pigmentation is determined by amount of UV radiation, vitamin D
destroyed by sunlight strong Uv radiation
-
r
and folate synthesis – the *Vitamin D/folate hypothesis
L crucial
dietary thing
*Jablonski & Chaplin 2010; no need to read this ref. You will watch the Jablonski TED talk
5
, balancing
Vitamin D/folate hypothesis of skin
• Pigmentation is determined by amount of UV radiation,
vitamin D and folate synthesis – the *Vitamin D/folate
hypothesis
We need UV radiation to synthesis of vitamin D
BUT
High UV radiation degrades folate
6
, Vitamin D/folate hypothesis of skin pigmentation
• Sunlight (UV radiation) is needed for synthesis of vitamin D in the
skin from pro- vitamin D mental health -
lcatalyzed
useful fora
lot of processes
programmed
cell death
_ during development
7
, Vitamin D/folate hypothesis of skin pigmentation
• Folate is an essential micronutrient with a central function in single
carbon transfer reactions
• Folate is needed for:
– converted into S-adenosylmethionine (SAMe) - primary methyl donor
necessary for numerous cellular reactions
– conversion of homocysteine to methionine and used for protein synthesis
– cell division, repair, and methylation of DNA synthesis
/ Nprttottein
☐
– maturation of red blood cells complex folate involved
,
in
many pathways
• hairless skin destroy
folate ,
need via min D
8
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