evolution of eye color elise wood 11/20/2014. ancestry of eye color what causes different shades...
TRANSCRIPT
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