EVOLUTION OF EYE COLOR

ELISE WOOD11/20/2014

What we will address:

Ancestry of eye color What causes different shades to appear

Mutation? Advantage? Large numbers decreasing to small numbers

• Human ancestors- Africa

• dark pigmentation- eyes, skin and hair

• were selected for due to hot temperatures/sunlight- darker pigmentation was advantageous

• Eye color is closely linked with skin color- genes are closely related

Ancestry of eye color

HOW IT ALL CHANGED… Human ancestors began to migrate to

various places around world

Selection for darker pigmentation wasn’t as high

• Mutation arose around Black Sea region

• OCA2 gene mutation

• Blue eyed people came from common ancestor with OCA2 mutation

• Inherited the same “switch” in the same spot in the DNA

• Spread of the mutation = advantageous?

Mutation? Advantage?

Theories:

Sexual selection- runaway selection like

peacocks

Sometimes blue eyes is linked with lighter skin

• Amounts of melanin

• Stroma- thick layer of melanin producing cells in iris

• OCA2 Gene

• OCA2 gene melanin production in eyes, hair and skin- P protein

• just affected the iris of the eye

Lipochrome

HERC2 gene + OCA2 gene

• Yellow pigmentation + blue = green

• Yellow + blue + little brown = hazel

• Rayleigh scattering – blue eyes

How are different shades “made”?

GENES TOOK OVER…

• 16 genes that are associated with eye color

• Offspring can have any eye color based on genes

• Alleles from each parent

• Combinations can be endless

• People are able to move all over the world and live in different

environments

• Blue eyed individuals are mating with brown eyed individuals- the

recessive blue gene becomes masked

• Genetics- the blue eyed gene usually loses out to the brown

Why are levels of eye color so different?

YouTube SciShow Video

SummaryBrown eyes are said to be the first eye color that our ancestors had

One common ancestor had a mutation in the OCA2 gene- passing it on over generations leading to blue eyes

Said to be some advantages to blue eyes, but none have been solidified

Mating and genes contribute to the lower levels of lighter eyes

Eye color will always vary- gene combinations/alleles/parent copies, etc.

References

http://evolution.about.com/od/humans/a/Evolution-Of-Eye-Color.htm

http://www.sciencedaily.com/releases/2008/01/080130170343.htm

http://genetics.thetech.org/ask-a-geneticist/origin-blue-eyes