Geneticists find an interesting source of Eye Colour

[Halden]

A team of Australian scientists have published a new study in the American Journal of Human Genetics that shows that eye colour is determined by a few letters of the DNA sequence and not Genes. A study of 4000 people demonstrated that a change of one letter in a SNP is all it takes to alter eye colour.

SOURCE (http://news.bbc.co.uk/2/hi/science/nature/6195091.stm)

[Zygar]

I find the title of the thread misleading. Most people would assume that you are implying that there is no genetic basis for eye colour. What you are saying is that eye colour is dependant not on an entire gene, but on a very short portion of a gene.

But this is cool stuff! It shows how few changes in a DNA sequence are necessary to create a major variation.

[Gilmar]

The article says genes ARE the source of eye color.

[ponderingturtle]

I find the title of the thread misleading. Most people would assume that you are implying that there is no genetic basis for eye colour. What you are saying is that eye colour is dependant not on an entire gene, but on a very short portion of a gene.

But this is cool stuff! It shows how few changes in a DNA sequence are necessary to create a major variation.

My understanding was that it was not in a gene but in the junk DNA portion around a gene.

Still not particularly well written article to explain what exactly was found.

Anyone here with enough genetic background to interpret?

[Aepervius]

But here is a relevant quote from the article :
"When OCA2 is knocked out, there is a loss of pigmentation. The position of these SNPs right at the start of the gene means it is possible we're looking at a change in the regulation of the gene in people with blue eye colour."

Functional change

So these SNPs, at the start of OCA2, probably regulate how much of the pigmentation protein is produced by the gene. People with brown eyes might have a lot of this protein, while people with blue eyes have less.

It seems that the mutation occurs at a specific position of the OCA2 gene, either changing its expression with a variety of degree (from supressing it to letting it fully with some intermediate), or changing its functionality, resulting in the various color.

I do not see anywhere in the article that the cahnge is in unexpressed DNA but maybe I misread....

[Paul C. Anagnostopoulos]

Here we go:

http://dienekes.blogspot.com/2006/11/human-eye-color-explained-by-three-snp.html

It's likely that the SNPs are regulatory and effect expression levels, although it could also be that they result in a protein change.

~~ Paul

[Paul C. Anagnostopoulos]

Halden, would you like me to change the title of this thread?

~~ Paul

[Orangutan]

My understanding was that it was not in a gene but in the junk DNA portion around a gene.
Snip.


I thought I read somewhere that geneticists were regretting the tag of "Junk" DNA as they were the "Junk" stuff actually had more uses that originally discovered.

Edit: maybe it was Wikipedia:
http://en.wikipedia.org/wiki/Junk_dna

[tracer]

SOURCE (http://news.bbc.co.uk/2/hi/science/nature/6195091.stm)


From the caption to the picture in the link:

there are about 2.9 billion base-pairs in the human genome wound into 24 distinct bundles, or chromosomes
We have 24 chromosomes now? Where did the other 22 go?

(And if they meant 24 chromosome pairs, then where did that new 24th pair come from?)

[hgc]

(And if they meant 24 chromosome pairs, then where did that new 24th pair come from?)
Just watch for the people with day-glo eyes. They're the 24 pair mutants.

[joobz]

Halden, would you like me to change the title of this thread?

~~ Paul
No, keep it. I'm think john Hewitt will get a kick out of it.

[athon]

I agree that the title of this thread is not just misleading, it's virtually the opposite of what the paper indicates.

Personally, I think this makes perfect sense in what we know about eye colour. Physiologically, its the placement of pigment in the layers of iris tissue that gives the variation. A small variation in a few base pairs could be all that's necessary to account for this, I guess.

Although I do remember reading somewhere that eye colour relies on something like a matrix of ten different genes. I wonder if this was wrong, or if it still requires a matrix of genes with variation relying on just one.

Athon

[Dark Jaguar]

I find the title of the thread misleading. Most people would assume that you are implying that there is no genetic basis for eye colour. What you are saying is that eye colour is dependant not on an entire gene, but on a very short portion of a gene.

But this is cool stuff! It shows how few changes in a DNA sequence are necessary to create a major variation.

Eye color isn't really major though. Think in terms of programming. In a web page, while adding an entire new feature requires a lot, if you already have a HEX code assigned to determine color, then all it takes is a single bit change in that hex color and you alter the color of the text it modifies.

However, by the same token a massive coded portion can all point to a single "bit" of code, depending on how it's coded, which will either activate or deactivate it completely. It isn't that that single bit codes for that feature, the other massive section does that, it's just that it is dormant until that single bit turns it on. The same could be true with DNA.

[Halden]

The study, which focused on twins, their siblings and parents, shows - conclusively - that there is no "gene" for eye colour.

The study concluded that is was a variation in the SNPs near the OCA2 gene that affect the amount of pigment in the eye and therfore it is not the Gene that decides. This is what I meant by the title and I apologize if this has mislead people.

Paul: Go ahead and change the title.

[athon]

The study concluded that is was a variation in the SNPs near the OCA2 gene that affect the amount of pigment in the eye and therfore it is not the Gene that decides. This is what I meant by the title and I apologize if this has mislead people.

Paul: Go ahead and change the title.

In that there is no 'blue' and 'green' colour? We've known that for quite some time, though. Even if the precise mutations are novel discoveries.

Athon

[Halden]

Wow, tough crowd. :(

I guess next time I will have to look for more substantial information.:book:

[athon]

Just have to watch the wording. So many arguments occur around these parts because two people who share similar views have a different understanding of definitions.

Please, don't be offended. Just expect anything you post to be torn apart and put back together again. It's actually quite an educational experience.

:)

Athon

[ponderingturtle]

I thought I read somewhere that geneticists were regretting the tag of "Junk" DNA as they were the "Junk" stuff actually had more uses that originally discovered.

Edit: maybe it was Wikipedia:
http://en.wikipedia.org/wiki/Junk_dna

Mabey. I just thought we knew the codes to look at and say stuff between code x and code y is a gene. Thus you can say you share 98% of your genes with a chip, but your DNA varies up to 40% from other humans.

Now it is not suprising that not all of the DNA not in genes is useless, but have they removed the idea of concidering a gene to be a select portion of the DNA?

[ponderingturtle]

Wow, tough crowd. :(

I guess next time I will have to look for more substantial information.:book:

Absolutely, it is an unwritten rule to haze the new people here right?

[Paul C. Anagnostopoulos]

Yes, it is, but so far Halden is doing quite well.

~~ Paul

[Halden]

I have no problem with the hard time as it only makes one try harder.

Thanks for the title change paul.

[Molinaro]

My eyes change color with my mood.

They are often brown with streaks of grey.
They are sometimes light green with streaks of grey.
They are sometimes orange.
They are sometimes very dark brown with no streaks.

[Orangutan]

My eyes change color with my mood.

They are often brown with streaks of grey.
They are sometimes light green with streaks of grey.
They are sometimes orange.
They are sometimes very dark brown with no streaks.

Sorry but I am skeptical (would you expect anything less), Are you sure they don't change with different lighting conditions. My eyes reportedly change from grey to green to blue but it generally reflects what color T-Shirt I am wearing.

Would mood changing eye color qualify as paranormal? You could win a $M!

My eyes change with photo-shop.
Sometimes they are blue,
sometimes green,
Mostly they reflect a screaming aggressive male orangutan.

[Molinaro]

I havn't done any scientific studies.. I just have my girfriend(s)' word to go by.

[ZirconBlue]

I havn't done any scientific studies.. I just have my girfriend(s)' word to go by.

Notoriously unreliable witnesses, girlfriends.

[Zygar]

Eye color isn't really major though. Think in terms of programming. In a web page, while adding an entire new feature requires a lot, if you already have a HEX code assigned to determine color, then all it takes is a single bit change in that hex color and you alter the color of the text it modifies.

However, by the same token a massive coded portion can all point to a single "bit" of code, depending on how it's coded, which will either activate or deactivate it completely. It isn't that that single bit codes for that feature, the other massive section does that, it's just that it is dormant until that single bit turns it on. The same could be true with DNA.

Yes, I agree about the dormancy. I am just pointing out how little it takes to make a fairly significant change.

And while eye colour doesn't seem that big, consider that many species of mammals have consistent eye colours across the species. And given how important eye colour is to us humans, I consider that variation to be rather significant.

[articulett]

People used to use eye color as a way of explaining recessive and dominant inheritance, but anyone can see that is an incorrect explanation because there are many variations between light blue eyes and dark brown eyes. The article is saying that eye color depends on how many "working" eye color alleles you have. The more you have, the more pigment that you will see in the eyes--unless you have 2 copies of the gene which causes albinism. Albinism makes it so that the eyes can't translate the genes for color, but they are still present as though the person wasn't an albino and these genes will be expressed in offspring (unless they happen to be an albino also.)

[luchog]

Sorry but I am skeptical (would you expect anything less), Are you sure they don't change with different lighting conditions. My eyes reportedly change from grey to green to blue but it generally reflects what color T-Shirt I am wearing..

That sounds like a particularly extreme example of colour change, but I've personally witnessed an ex-girlfriend's eye colour change from hazel to a pronounced green with no change in lighting or in anything that could be reflected (such as clothing), or even a change in position. The change occurred at the same time as... certain other physiological changes, in accordance with... certain external stimuli. :D

I've also noticed relatively minor changes in mine and others that seem to mirror, not mood, but physiological states (health, stress, etc). And being that I, and many of my aquaintances, tend to wear exclusively black clothing the vast majority of the time, it wasn't 'cause of a shirt colour change.

[Modified]

That sounds like a particularly extreme example of colour change, but I've personally witnessed an ex-girlfriend's eye colour change from hazel to a pronounced green with no change in lighting or in anything that could be reflected (such as clothing), or even a change in position. The change occurred at the same time as... certain other physiological changes, in accordance with... certain external stimuli. :D

I've also noticed relatively minor changes in mine and others that seem to mirror, not mood, but physiological states (health, stress, etc). And being that I, and many of my aquaintances, tend to wear exclusively black clothing the vast majority of the time, it wasn't 'cause of a shirt colour change.

What about a change in pupil size affecting the color?

[CapelDodger]

I havn't done any scientific studies.. I just have my girfriend(s)' word to go by.
Have you considered that the observed colour might change with your girlfriend's mood? In my experience anything's worth considering as a possible clue to a woman's mood, my experience being one of having far too few clues. On occasion, so I've been told, no clue at all.

[CapelDodger]

What about a change in pupil size affecting the color?
Oh, I get it now, luchog was talking about drugs.

[CapelDodger]

Wow, tough crowd. :(

I guess next time I will have to look for more substantial information.:book:
I'm sure you'll excuse people - me included - who couldn't immediately distinguish you from the "What about this, eh? Eh? It's science!" numpties who crop up here. Notice how the reaction was softly spoken and tentative but implied the big stick.

To avoid the T'ai Chi effect, always make a meaningful comment or ask a question in an opening post. Or alternatively never start a thread (I don't, I just leech on other people's).

Welcome :) . And Happy Solstice Everybody!

[CapelDodger]

And while eye colour doesn't seem that big, consider that many species of mammals have consistent eye colours across the species. And given how important eye colour is to us humans, I consider that variation to be rather significant.
How much selection pressure does eye colour exert? Poets might make a big thing of it in recent times but I can't help thinking genetic drift gave them the material to play with. Compared to figure, face and fortune eye-colour is an afterthought. OK, it worked for Steve McQueen, but what proportion of the women he could have impregnated did he actually impregnate? A very small one. I rest my case.

Damn, I love Solstice.

[athon]

Mabey. I just thought we knew the codes to look at and say stuff between code x and code y is a gene. Thus you can say you share 98% of your genes with a chip, but your DNA varies up to 40% from other humans.

Now it is not suprising that not all of the DNA not in genes is useless, but have they removed the idea of concidering a gene to be a select portion of the DNA?

The precise definitions for 'gene' have been argued in recent years. Once, genes were only considered to be codes, and as such, had a particular structure in which the code could interact with particular enzymes in order to be translated. Now we know that there are constructs throughout the genome which act physically in order to assist with genetic expression. Some describe these as genes, even though they don't have the typical structure of one.

Athon

[athon]

How much selection pressure does eye colour exert? Poets might make a big thing of it in recent times but I can't help thinking genetic drift gave them the material to play with. Compared to figure, face and fortune eye-colour is an afterthought. OK, it worked for Steve McQueen, but what proportion of the women he could have impregnated did he actually impregnate? A very small one. I rest my case.

Damn, I love Solstice.


It might have a lot to do with reading facial expression. Blue eyes are easier to watch for subtle eye movements than brown eyes are.

Eyebrows are thought to play a role in this; the movements of eyebrows detail emotions better than those who don't have them.

Athon

[ZirconBlue]

What about a change in pupil size affecting the color?

For example, many people think that David Bowie has two differently colored eyes, when in fact he just has one pupil that is always dilated.

[Zygar]

How much selection pressure does eye colour exert? Poets might make a big thing of it in recent times but I can't help thinking genetic drift gave them the material to play with. Compared to figure, face and fortune eye-colour is an afterthought. OK, it worked for Steve McQueen, but what proportion of the women he could have impregnated did he actually impregnate? A very small one. I rest my case.

Damn, I love Solstice.

I don't remember mentioning selection pressure. Only that we make a big deal over eye colour.

[CapelDodger]

I don't remember mentioning selection pressure. Only that we make a big deal over eye colour.
People make a big deal of mobiles or cars. Poets made eye-colour a thing when they ran out of tit-references. It's not important at a genetic level, which is kinda the scope of this thread.

[articulett]

Actually, the perceived change in eye color is probably an illusion based on clothing and surround colors--
To see how readily your color perception can be altered, check out these illusions:
http://www.johnsadowski.com/big_spanish_castle.php (my favorite)
http://www.planetperplex.com/en/img.php?id=166 (shows how contrast messes with color perception)
http://www.planetperplex.com/en/img.php?id=35
http://www.mindfake.com/illusion_55.html
and this one is a rather rude joke that colorblind people can't get:
http://www.tshirthell.com/store/product.php?productid=559

Although you may notice a persons eyes more as their mood changes and as the pupil dilates and constricts with lighting--it is unlikely that the pigment is actually undergoing any alterations. The more likely explanation is your perception is leading to the illusion that the eyes are changing colors.

[articulett]

I also think that people are unaware of how lighting and such changes color. If you do a color sample of skin or eyes or teeth in photoshop, you get a whole pallet of different colors in a single eye when sampling by pixel. Eyes and teeth and skin look one color--but they are clearly a blend of multiple colors, reflections of light, etc. But our eyes see this blend as "one color".

Skin color and hair color are also inherited similarly to eye color--with the more "working" melanin genes you inherit, the darker skin and hair will be. Red hair is a mutation of the traditional "working" color allele which you can only see if there are not too many "melanin" genes to cover it up. If you have dark hair, you could be carrying the red hair mutation and not know it.

[CapelDodger]

It might have a lot to do with reading facial expression. Blue eyes are easier to watch for subtle eye movements than brown eyes are.
The brown-eyed guy that sold you that idea - did you ever meet his boss?

Eyebrows are thought to play a role in this; the movements of eyebrows detail emotions better than those who don't have them.

Athon
There's a lot to faces, so let's face it, eye-colour is the last thing you're weighing-up in a poker game. Eye-movement isn't actually a subtle signal, for subtlety you have to look to nostrils.

[articulett]

Here is a page of optical illusions--http://websearch.about.com/gi/dynamic/offsite.htm?zi=1/XJ&sdn=websearch&zu=http%3A%2F%2Fwww.skytopia.com%2Fproject%2Fillus ion%2Fillusion.html

Go to the one called "vanishing fluff" to see colors disappear before your eyes.

And here's an image where children see a vase with dolphins, but adults do not. http://www.frenblog.com/illusion/dolphin-illusion/ (I've actually asked an 8 year old.)

Jerry Andrus' optical illusions are always on display at TAM. Our visual perception is prone to particular types of errors; so are their memories. I'm guessing that sort of phenomena is behind the belief that a persons eyes change color with their moods, clothing change, etc. Of course there could be some shifting pigment phenomena that no one has discovered yet, but I'm skeptical.

[articulett]

For example, many people think that David Bowie has two differently colored eyes, when in fact he just has one pupil that is always dilated.

Yes, that's true...because our color perception involves an averaging out of the colors we see. Blue eyes are more readily "readable" because pupil dilation is associated with arousal (be it a good poker hand or something else that increases adrenalin)--Brown eyed people are thought to be warmer, but this is probably due to the fact that small pupils are not as noticeable as they are against light blue eyes (they don't seem as "cold" when their pupils are constricted.) I don't know if there is an actual reproductive advantage for any particular eye color, but in climates exposed to a lot of sun, brown eyes offer protection against cataract formation. (Melanin's main effect is to protect from sun damage--for both skin and eyes). I think blue eyes may be more valued because they are rarer, but as Paris Hilton shows, they are very easy to fake now that color changing lenses are available.

[articulett]

Wow, tough crowd. :(

I guess next time I will have to look for more substantial information.:book:

Clearly, it's an interesting topic even if people have problem with your title. We've known for some time that eye color was an additive genetic trait...but prior to this, we hadn't pinpointed these genes were located. Now, theoretically, we can tell you where a fetus will fall along the spectrum of eye colors by adding up the copies of working eye color genes (no working copies means light blue eyes by default.). Theoretically this means that people can do pre-implantation genetics and discard the brown eyed embryos--to increase the odds of having a blue eyed child, but it seems like an expensive method considering how easily eye color can be changed to any color you want with contacts...heck, you can change them by the hour to reflect your mood if you want!

[articulett]

Welcome :) . And Happy Solstice Everybody!

Thanks. I hadn't realized but today, is indeed, the winter solstice. This is the shortest day (measured in daylight) in the Northern hemisphere, but is it the longest day for our Australian forum members? (Another digression, but I have to ask...Do flat maps of the world in Australia have Australia in the center? In the United States, most world maps show the United states towards the center in the upper left quadrant (Northwest) and Australia in the Southeast. Do your maps look the same? It's not completely off topic since we are talking about "perception".)

[luchog]

Oh, I get it now, luchog was talking about drugs.

No, but that certainly explains some of your posts.

[blutoski]

From the caption to the picture in the link:


We have 24 chromosomes now? Where did the other 22 go?

(And if they meant 24 chromosome pairs, then where did that new 24th pair come from?)

Depends on the context.

1-22 (paired), plus x and y. 24 'kinds' of chromosomes in the genome.

Or, you could say 44 (paired) + 2 sex chromosomes, actually in each cell.

Or, you could say 46 functioning in a male's cells, 45 functioning in a female's cells (the extra X is compressed into a Barr body).

&c. I wouldn't worry about it.

[blutoski]

My understanding was that it was not in a gene but in the junk DNA portion around a gene.

Still not particularly well written article to explain what exactly was found.

Anyone here with enough genetic background to interpret?

The abstract explicitly says the location of interest is in the intron, which means it's not junk dna. The gist of the article is that very little change in genome can translate into a wide range of noticeable difference in phenotype.

It's also worth noticing that these three SNPs control - they estimate - 76% of phenotype... it follows that they haven't put their finger on the origins of the other 24%.

(I'd like to know where gold flecks come from.)

[DRBUZZ0]

Just as an aside, which may or may not be of interest. I have two distant cousins (sisters) who both have an interesting condition. They both have two different color eyes, one is very deep blue and the other is hazel. Both of them also have one normal eye and one eye with a somewhat unusual iris.

Their iris is missing a small section and the pupil opening is slightly off center, resulting in a "keyhole" shaped pupil. There's no ill effect other than a slightly greater sensativity to bright glare in one eye.

but what is strange is that the medical opinion on this condition is that it is rare, but thought not to be genetic. Rather it is presumed to be a random fluke in development of the eye.

However, the chances of that seem slim, given that both of them (sisters, not twins though) have it in the exact same way. Their brother does not and nor does their father or mother.

Here's a pic. Yes..it has been Photoshopped I didn't Photoshop it because I'm making this up, but because the poor resolution glare in the eyes, in all the pictures I have, makes it very difficult to see. This has been adjusted to give a better impression of how it looks in person...


Just gives some idea of some of the things which are not yet completely understood