Biology Question about Green Eyes

College Life
1

<p>If green are dominant over blue eyes, then why are green eyes rarer than blue eyes?</p>

2

<p>First, just because a gene is dominant doesn't mean that it's the most prevalent gene in the gene pool. For example, [polydactyly</a> <a href="having%20more%20than%20five%20fingers%20or%20toes%20on%20one%20hand/foot">/url</a> is dominant, but you don't see all that many people walking around with six fingers. </p>

<p>The frequency of a gene has to do with a lot of factors, some of which have to do with the selective value of the gene and some of which have to do with random factors. For example, the frequency of various [url=<a href="http://anthro.palomar.edu/vary/vary_3.htm%5Dblood"&gt;http://anthro.palomar.edu/vary/vary_3.htm]blood&lt;/a> type alleles](<a href="http://www.ncbi.nlm.nih.gov/entrez/dispomim.cgi?id=174200%5Dpolydactyly"&gt;http://www.ncbi.nlm.nih.gov/entrez/dispomim.cgi?id=174200) varies markedly between people from different regions of the world. In some cases, the increased frequency of a certain type can be related to selection against people who don't carry the type (in populations with endemic cholera, type O blood is more frequent). In other cases, the distribution seems to be related merely to the distribution in the founding population (Native Americans have a distribution which resembles that of Asians, because the ancestors of Native Americans came to North/South America from Asia over the Bering land bridge).</p>

<p>Also, eye color is a polygenic trait, meaning that it's not determined by alleles at only one locus. (I know, I know, that's how your high school biology teacher taught it. He/she lied!) The National Institutes of Health [url=<a href="http://www.ncbi.nlm.nih.gov/entrez/dispomim.cgi?id=227240%5Dsays%5B/url"&gt;http://www.ncbi.nlm.nih.gov/entrez/dispomim.cgi?id=227240]says[/url&lt;/a&gt;]


</p>

3

<p>I love how on CC, one can ask a 9th grade level introductory biology and have it answered by an MIT senior majoring in the subject.</p>

4

<p>yeah if its dominant it doesn mean it will be more common. it jsut means that the person who has the dominant gene will have green and not blue eyes.</p>

5

<p>Here's another eye question (just because I'm curious & putting off studying for finals):</p>

<p>Everyone on my mother's side of the family has blue eyes; everyone on my father's side of the family has brown eyes. I have eyes that are light brown around the pupil and blue/green/grey on the outside. My eye color also changes depending on the time of the day, my mood, etc.</p>

<p>Why did this happen? Nobody in the last ~3 generations on either side of my family had/has eyes like mine. For that matter, what is the official term for the color of my eyes? I've heard "true hazel," but they are definitely NOT hazel... (You can imagine the problems I've had with deciding what eye color to put down on official documents and forms!)</p>

<p>Thanks :)</p>

6

<p>Well, I'm not Mollie, but I can answer the last question (courtesy of one of my friends, who has a bio degree). I have eyes that used to be dark brown; then they were light brown. Now they are a little brown, mostly green. </p>

<p>Basically, even with a dominant/recessive trait, the recessive trait can take over later on in life or the dominant trait can take a while to become dominant. With me, the brown is losing out over time to the green; forget the exact term for this (Mollie!) but it happens. </p>

<p>If you EVER figure out what colour eyes you have, let me know. I'm wondering myself (hazel? blonde? - yes, they used to match my hair and people thought I wore contacts. brownish/greenish/bluish? Moldy peanut butter?) and would love to know. Don't know if you ever get guys trying to pick you up... "I can't decide what colour your eyes are." (You're never gonna find out, buddy.)</p>

7

<p>I have to admit I don't know much concretely about eye color, but I am happy to speculate.</p>

<p>I found a [url=<a href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=16280011&query_hl=6&itool=pubmed_docsum%5Dpaper%5B/url"&gt;http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=16280011&query_hl=6&itool=pubmed_docsum]paper[/url&lt;/a&gt;] which I'm referencing here. (Can you see it from that link?) The citation is
Wielgus AR, Sarna T. "Melanin in human irides of different color and age of donors." Pigment Cell Res. 2005 Dec;18(6):454-64.</p>

<p>Color in the ring around the pupil is caused by the relative amount of a pigment protein called melanin (the same stuff that makes moles and freckles brown). People who have more melanin (= more or more productive melanin-producing cells) have brown eyes, while people with very little melanin (= fewer or less productive melanin producing cells) have blue eyes. There are several other sources of color variation: melanin comes in a few different forms (pheomelanin and eumelanin, and probably others), and color can be modulated by iron molecules in the eye.</p>

<p>
[quote]

It appears that the iris color fully develops during infancy.... pigment production is not normally observed during later stages of organism development. Thus, the characteristic color of the eye... does not change significantly during the lifetime. This should not lead to a conclusion that melanin content and/or its structure do not undergo any changes at all. Indeed, some epidemiological studies suggest that the human irides become lighter at older age.

[/quote]
</p>

<p>So it seems like what's happening is that there's variation in the production of melanin, both across the area of the iris (in atmjunk's case) and in time (in ariesathena's). The reason for this is probably complicated, and can't be well-described by just referring to dominant or recessive genes. Basically, for whatever reason, the genes for melanin are transcribed at different frequencies at different times/areas of the eye.</p>

8

<p>i thought eye color determination was a lot more complicated than just a simple cross of alleles</p>