Eye Color Question

[evomom]

Okay, bear with me, please. I grew up in a religious household that shunned science and am now struggling to make up for lost time. As a first step in learning, I am currently reading a children's book on evolution. The author mentions that blue eye color is a mutation. I thought it was a trait. Reading up on what mutations and traits are, I am confused; what are the differences between the two? They sound so similar.

Also, if our ancestors all started out with brown eyes and blue eye color makes someone more susceptible to sun-related eye problems, then why would a mutation occur for blue eyes?

Any book/website suggestions to learn about this stuff as simply as possible are appreciated! The sites I went are chockfull of information that's pretty much over my head right now. I have such a ways to go in learning.

 

[elte]

Okay, bear with me, please. I grew up in a religious household that shunned science and am now struggling to make up for lost time. As a first step in learning, I am currently reading a children's book on evolution. The author mentions that blue eye color is a mutation. I thought it was a trait. Reading up on what mutations and traits are, I am confused; what are the differences between the two? They sound so similar.

Also, if our ancestors all started out with brown eyes and blue eye color makes someone more susceptible to sun-related eye problems, then why would a mutation occur for blue eyes?

Any book/website suggestions to learn about this stuff as simply as possible are appreciated! The sites I went are chockfull of information that's pretty much over my head right now. I have such a ways to go in learning.

I like your new curiosity for knowledge. I'm glad you are here on the forums. I think you have said it correctly in that the mutation could get passed down as a trait. I will like to wait and see if someone more versed in genetics would like to explain it, even if I might know somewhat how to explain it.

 

[cosmictraveler]

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. Before then, there were no blue eyes.

"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.

http://www.google.com/url?sa=t&rct=...-b2sAg&usg=AFQjCNE42aIpOKhU5yPb7OiP0DEqyGr_hQ

 

[skaught]

It is a mutation, and a trait. Once a mutation happens in an individual, that particular mutation is now a trait in that persons DNA. Which they will then pass on to their offspring.

Not all mutations are always beneficial to the given environment. However, because there is far less sun in the north than there is by the equator, then having blue eyes wouldn't have been as much of a liability. It may very well have been an aesthetic thing. If you were the first and only blue eyed person in the world, people would probably have been really attracted to you. Therefore, you would have many more offspring.

 

[Ophiolite]

First a word of congratulations. I applaud your effort to learn of this important topic and to do so coming froma background that would have discouraged this.

Secondly, a word of caution. Treat everything your read sceptically. Don't believe something simply because someone in authority says so. On the other hand if several authorities tell you the same thing and they provide the evidence to support that, then provisionally accept it as factual. (Everything in science is always provisional, it's just that some things are more provisional than others.)

As to your questions: blue eyes are both a trait and a mutation. They are a trait, in that their presence, or absence, is controlled by our genetic makeup.

If we inherit the genes for blue eyes from both parents then we will have blue eyes. If we inherit the gene for blue eyes from only one parent and for brown eyes from the other we will have brown eyes, since the gene for brown eyes is a dominant gene and for blue eyes a recessive gene. (It is actually more complicated than that: you can find a slightly more detailed, but still simple, explanation here:http://www.brighthub.com/science/genetics/articles/22176.aspx).

But blue eyes, or rather the gene for blue eyes is also a mutation. It occured, probably a number of times in some of our ancestors, then spread through the population.

You ask why would it occur? Well most mutations are either neutral or harmful. They occur by chance, not as a means of improving the fitness of the organism. By chance a small percentage of mutations will offer some advantage to the organism.

I don't know the details for the blue eye gene, but here are some thoughts. Where did blue eyed people evolve? In the far north, where - trust me on this one - there is precious little sun, so that the disadvantage of the gene may have been quite minor, or even absent. Moreover, there may be some advantage confederred by blue eyes. Certainly in some societies the blue eyed person will be favoured over the brown eyed as a potential mate - that's sexual selection an important compliment to natural selection.

Also, the gene that controls the eye colour may be controlling other things too and these may confer advantages. The specifics in this area lay outside of my expertise.

Have you looked at wikipedia articles such as this one on genetics: http://en.wikipedia.org/wiki/Genetics.

Don't try to absorb it all in one sitting, but reading a number of articles like that will allow you to become familiar with the language. There are many excellent books on evolution. I'm not a great fan of Richard Dawkins, but two of his works The Ancestor's Tale and The Greatest Show on Earth are both good. Also, as a direct repsonse to creationist arguments Why Evolution is True by Jerry Coyne may be a good choice for you.

Edit: I see I took so long to complete this that several others have already made the same points. My apologies for the repetition.

 

[evomom]

Thanks for your responses. It's making more sense to me (and sparking my curiosity further). I will check out the links soon.

And, Ophiolite, there's no need to apologize. From where I'm at, repetition is a good thing.

 

[scheherazade]

Welcome to the forum evomom.

You may find the following brief video presentation helpful: Genetic Traits: Eye Color, by Joshua Page



Click on image to start.

 

[KilljoyKlown]

I agree with skaught and appreciate Ophiolite's detail on the subject. I know the OP narrowed the scope to blue eye color, but much the same can be said about other non-brown colored eyes.

When I was in high school I knew a natural blond woman who had one very blue eye and one very green eye. It was amazing to say the least, after that I've always liked green eyes. I found some info and pictures of green eyes.

Green Eyes are less than 2 % of worlds population. They are the only eye color that changes colors.. more blue, more grey, more green depending on the weather and mood. Green Eyes are the best and rarest.

As in the case of blue eyes, the color of green eyes does not result simply from the pigmentation of the iris. Rather, their appearance is caused by the combination of an amber or light brown pigmentation of the stroma, given by a low or moderate concentration of melanin, with the blue tone imparted by the Rayleigh scattering of the reflected light.

Green eyes probably result from the interaction of multiple variants within the OCA2 and other genes. They were present in south Siberia during the Bronze Age. They are most common in Northern and Central Europe. They can also be found in Southern Europe and North Africa. In fact, Turkey, at 20%, is the country with the largest percentage of green eyes. In Iceland, 89% of women and 87% of men have either blue or green eye color. A study of Icelandic and Dutch adults found green eyes to be much more prevalent in women than in men. Among European Americans, green eyes are most common among those of recent Celtic and Germanic ancestry, about 16%.

 

[Aqueous Id]

As a first step in learning, I am currently reading a children's book on evolution. The author mentions that blue eye color is a mutation.

Good for you, and good for the educators who want youngsters to understand mutation.

Also, if our ancestors all started out with brown eyes and blue eye color makes someone more susceptible to sun-related eye problems, then why would a mutation occur for blue eyes?

Melanin affects both eye and skin color. The amount of melanin depends on genetics and light exposure. Blue eyed newborns coded for brown eyes begin producing melanin with light exposure and the eyes turn brown as they mature.

This is connected to skin coloration then.

Here is a rationale for evolving a fair, blue eyed trait:

You already know fair skin is susceptible to skin cancer. You also need to know that Vitamin D is manufactured by sunlight on the skin. Fair skin collects more Vitamin D. Lower melanin gives lighter skin, bluer eyes. The northern latitudes receive less sunlight. Less sunlight yields lower Vitamin D. Less melanin lightens the skin, restoring Vitamin D production. The risk of cancer is balanced, because there is less sunlight.

For more info:

Why Are My Eyes Blue? The Genetics of Eye Color

 

[aaqucnaona]

Okay, bear with me, please. I grew up in a religious household that shunned science and am now struggling to make up for lost time. As a first step in learning, I am currently reading a children's book on evolution.

You must read about science before you do evolutionary biology. The absolute best book I can just is:
The magic of reality.
http://isohunt.com/torrent_details/351689585/?tab=comments
http://en.wikipedia.org/wiki/The_Magic_of_Reality:_How_We_Know_What's_Really_True

The author mentions that blue eye color is a mutation. I thought it was a trait.

A trait is any characteristic that is specific to a species or a population. Eye colour, average height, skin color are traits. A mutation is a random change in the genes [it happens because 3 billion pair of gene information cannot be always replicated perfectely, so mistakes happen, slightly tweeking the traits that the gene creates]. Genes affect traits because genes determine how the embreyo turns out to be like.

Also, if our ancestors all started out with brown eyes and blue eye color makes someone more susceptible to sun-related eye problems, then why would a mutation occur for blue eyes?

Mutations themselves are completely random. Just because blue eyes may be harmful doesn't mean the mutations for blue eyes wont happen. Similiarly, giraffes dont have more mutations for longer necks if tree grow taller. Instead, more giraffes with randomly arising longer necks survives, so the effect is the same as there being more longer necks. The blue eyes may not be a problem big enough to actually kill the person, in which case the person will have children and the blue eyes will spread.

Any book/website suggestions to learn about this stuff as simply as possible are appreciated! The sites I went are chockfull of information that's pretty much over my head right now. I have such a ways to go in learning.

This is the absolute must have -
http://www.amazon.com/Magic-Reality-Know-Whats-Really/dp/1439192812

Sites -

http://en.wikipedia.org/wiki/Introduction_to_evolution [use the hyperlinks to learn more on specific topics].

Plus, even if you hate dawkins [because he is an atheist {like most of us here}], you must read his books on biology because he is the most prominent evolutionary biologist of our time - he is the new charles darwin just like stepeh hawkin is the new einstein.
His books -
http://thepiratebay.ee/torrent/5693142/Richard_Dawkins_-_E-Books_Collection_2010

And last but not the least - welcome to the bright side of the world!

 

[michael_taylor]

....?

Your questions about biology seem to have been dealt with, I just wanted to add my agreement to the earlier suggestion to learn the general method of science before specifics.

To that end I'd suggest;
http://www.youtube.com/watch?v=EYPapE-3FRw
...which is a video featuring Richard Feynman, and also the book "The Demon-Haunted World" by Carl Sagan, which is very accessible and even quite entertaining.

As for evolution, if you really can't wait, I'd suggest "The Origin of Species" by Charles Darwin. It doesn't have all sorts of jargon and technical detail, it's written quite like a story.

 

[chimpkin]

I wonder how I ended up with hazel eyes precisely, and I guess that isn't answered yet.
If it were a matter of simple dominance, I would have ended up with brown eyes, or possibly blue if my dad carried it as a recessive.
Instead my eyes are...pondscum-colored.