Thursday, January 31, 2008

Incest in Romance Novels? Fuel to the Fire....

Scientists find that blue-eyed individuals have a single, common ancestor

Image: Reese Witherspoon
Carolyn Kaster / AP file
How did actress Reese Witherspoon get those big blue eyes? A team of scientists has found that blue eyes are linked to a genetic mutation that occurred between 6,000 and 10,000 years ago.

A team of scientists has tracked down a genetic mutation that leads to blue eyes. The mutation occurred between 6,000 and 10,000 years ago, so before then, there were no blue eyes.

"Originally, we all had brown eyes," said Hans Eiberg from the Department of Cellular and Molecular Medicine at the University of Copenhagen.



The mutation affected the so-called OCA2 gene, which is involved in the production of melanin, the pigment that gives color to our hair, eyes and skin.

"A genetic mutation affecting the OCA2 gene in our chromosomes resulted in the creation of a 'switch,' which literally 'turned off' the ability to produce brown eyes," Eiberg said.

The genetic switch is located in the gene adjacent to OCA2 and rather than completely turning off the gene, the switch limits its action, which reduces the production of melanin in the iris. In effect, the turned-down switch diluted brown eyes to blue.

If the OCA2 gene had been completely shut down, our hair, eyes and skin would be melanin-less, a condition known as albinism.

"It's exactly what I sort of expected to see from what we know about selection around this area," said John Hawks of the University of Wisconsin-Madison, referring to the study results regarding the OCA2 gene. Hawks was not involved in the current study.

Baby blues
Eiberg and his team examined DNA from mitochondria, the cells' energy-making structures, of blue-eyed individuals in countries including Jordan, Denmark and Turkey. This genetic material comes from females, so it can trace maternal lineages.

They specifically looked at sequences of DNA on the OCA2 gene and the genetic mutation associated with turning down melanin production.

Over the course of several generations, segments of ancestral DNA get shuffled so that individuals have varying sequences. Some of these segments, however, that haven't been reshuffled are called haplotypes. If a group of individuals shares long haplotypes, that means the sequence arose relatively recently in our human ancestors. The DNA sequence didn't have enough time to get mixed up.

"What they were able to show is that the people who have blue eyes in Denmark, as far as Jordan, these people all have this same haplotype, they all have exactly the same gene changes that are all linked to this one mutation that makes eyes blue," Hawks said in a telephone interview.

Melanin switch
The mutation is what regulates the OCA2 switch for melanin production. And depending on the amount of melanin in the iris, a person can end up with eye color ranging from brown to green. Brown-eyed individuals have considerable individual variation in the area of their DNA that controls melanin production. But they found that blue-eyed individuals only have a small degree of variation in the amount of melanin in their eyes.

"Out of 800 persons we have only found one person which didn't fit — but his eye color was blue with a single brown spot," Eiberg told LiveScience, referring to the finding that blue-eyed individuals all had the same sequence of DNA linked with melanin production.


"From this we can conclude that all blue-eyed individuals are linked to the same ancestor," Eiberg . "They have all inherited the same switch at exactly the same spot in their DNA." Eiberg and his colleagues detailed their study in the Jan. 3 online edition of the journal Human Genetics.

That genetic switch somehow spread throughout Europe and now other parts of the world.

"The question really is, 'Why did we go from having nobody on Earth with blue eyes 10,000 years ago to having 20 or 40 percent of Europeans having blue eyes now?" Hawks said. "This gene does something good for people. It makes them have more kids."





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9 Comments:

Anonymous Bev Stephans said...

That is so interesting! I have a weird situation in my family. My father and mother had blue eyes. My 2 brothers and my sister have blue eyes. I have hazel eyes, leaning more to green. Yes, I am their child. My sister and I could be twins if it weren't for the almost 14 year age difference. my ex-husband has brown eyes and my 2 sons have brown and gray eyes respectively. That's quite a gene pool. Dive in, the water's fine.

January 31, 2008 11:11 PM  
Blogger Ann Wesley Hardin said...

Hey Bev, it's the same in my family! The parents had blue eyes, me and both brothers had blue eyes, and FabOne has hazel! Haha. This isn't the first time we found something in common, but I can't for the life of me remember what it was -- the names/ natures of our sibs, I think?

How cool.

February 01, 2008 10:51 AM  
Anonymous Bev Stephans said...

We both have sisters with the same name and had brothers with the same name. Is FabOne the oldest or youngest?

February 01, 2008 3:05 PM  
Blogger Ann Wesley Hardin said...

FabOne is older than me, but my brothers were older than both of us. So, she's the dread third child, though if you want to get technical, she could be considered a first born since there's a huge age difference between the boys and us. Same parents though!

Don't tell me you're the third child too. That would be too Twilight Zone...

February 01, 2008 9:26 PM  
Anonymous Jane/FabONE said...

dread third child?!

The way I remember it is - darling daughter number one

:)

--which used to peeve number two....

February 01, 2008 9:47 PM  
Anonymous Bev Stephans said...

No, I'm the eldest in the family!

FabOne, I like that: Darling daughter number one!

February 02, 2008 2:24 AM  
Anonymous jane/fabdame said...

Thanks Bev. That was our Dad's pet names for us - we knew we were loved.
I have a mixed bag of birth order stuff as there was almost a decade gap between the boys and me - I kinda qualify as a first-born (as #2 :) was explaining).

February 02, 2008 10:26 PM  
Anonymous Bev Stephans said...

Jane, my Dad had a lot of pet names for us. They would vary with his mood, from silly to kind of angry. He never got real angry with us unless we did something life-threatening.

Our family was spread out. I was number 1, followed by my eldest brother 4 1/2 years later, followed by my youngest brother 7 years later and finally my sister almost 14 years later. In spite of the age gaps, we have always been pretty close. Of course, being the oldest I came in for a lot of baby sitting. Gratis, I might add.

February 03, 2008 1:25 AM  
Anonymous jane/fabdame said...

But you're not bitter - eh Bev?

Yes, the oldest has to be extra good and be the example, responsible, etc.

Got to take the bad with the good. Being a sort of oldest endows one with confidence. ;)

February 03, 2008 3:11 PM  

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