Posted on 05/31/2009 1:23:07 PM PDT by SunkenCiv
What most people know about the inheritance of eye color is that brown comes from a dominant gene (needing one copy only) and blue from a recessive gene (needing two copies). University of Queensland geneticist Rick Sturm suggests that the genetics are not so clear. "There is no single gene for eye color," he says, "but the biggest effect is the OCA2 gene." This gene, which controls the amount of melanin pigment produced, accounts for about 74 percent of the total variation in people's eye color.
Sturm has recently shown that the OCA2 gene itself is influenced by other genetic components. After gene-typing about 3,000 people, Sturm found that how OCA2 is expressed -- and how much pigment a person has -- is strongly linked to three single nucleotide polymorphisms (SNPs), or single letter variations, in a DNA sequence near the OCA2 gene. That suggests a more complicated story than the blue-recessive/brown-dominant model of eye color. "For example, among individuals carrying the SNP sequence "TGT" at all three locations on both copies of the gene, 62 percent were blue-eyed," says Sturm's colleague David Duffy. By contrast, only 21 percent of individuals carrying only one TGT copy at each location and 7.5 percent of those lacking the TGT entirely had blue eyes.
Depending on the particular combination of SNPs inherited, a person can have a range of OCA2 activity that lands them on the spectrum between blue and brown eyes. What about green eyes? "Green eyes probably represent the interaction of multiple variants within the OCA2 and in other genes, including perhaps the red-hair gene," Duffy says.
(Excerpt) Read more at discovermagazine.com ...
As a kid my eyes were blue like top center but are not green likd middle left.
When in my twenties my eyes were stil blue, but when I drank they went very green.
All of my siblings and parents (7 total) have center top blue. I have center...green, I guess.
"About 74%" is a perfectly legitimate way to express a more precise number like 73.89%.
I would have had a hard time believing it myself, but it happened to ME!
Well, it does give the night bright colors.
"Green eyes probably represent the interaction of multiple variants within the OCA2 and in other genes, including perhaps the red-hair gene," Duffy says.:') Hair color is in that boat -- that is, true red hair has a different color, while everyone else (other than albinos I suppose) has varied levels of a single pigmentation. Maybe that's why the guy suggests that.
What good would that do anyone? ;’) Probably red hair and green eyes depends on having two X chromosomes...
...or so the dad likes to think. ;’) Probably atavistic, from one or both of their sides of the family, white ancestors in the woodpile.
*snort*
If yore purdy, it don’t matter none. ;o]
Eye color is an example of what biologists call "continuous variation" - a trait that is obviously influenced by multiple genes. I always remind my students that this is the case even while I am using eye color as an example of a simple Mendelian trait.Well, that's just mean. ;') ;')
Celtic, Romanian, Jewish and UkrainianHey, at least it rhymes.
Kinda makes it hard to refute, doesn’t it?
Wow!
Must be some extraterrestrial DNA... [spooky organ sounds]
I’m just glad I’ve *got* eyes. Although it would be cool to have Steve Austin’s $6 million dollar man eyes...
Oh I see, numbering the different examples above... I’m not even on there, just noticed this. I’m darker than the darkest, like rich columbian coffee. Or manure, depending on what I’ve just said to somebody...
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