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Eye color inheritance explained
- Mar 24, 2009 at 5:22 AM
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- Comments (17) Total Views (944) Everyone can see this journal post.
banner above editied from a picture from analtech.com
Eye color inheritance is probably the topic of most genetics questions I see on CafeMom. And unfortunately, the answers people get are almost always wrong, or at minimum, over-simplified.
Genetics is an complicated field that requires an understanding of molecular biology in order to fully grasp. Understanding a Punnett Square does not make you a geneticist, nor does it qualify you to answer questions on inheritance. Even if you are one smart chick. If you really want to know how eye color is inherited, read on. Feel free to skip down to the take-home message in red if you aren't interested in details.
The Basics of Genetics
When you were conceived you received one set of genes (DNA) from your mom and one from your dad. There is a copy of this set of genes in most cells of your body. Each cell uses the genes it needs to perform its specific function. For example, heart cells will turn on genes that brain cells won't. We call this 'gene expression'. Gene expression is a complicated process where DNA is used as an 'instruction book' to make a wide variety of proteins. Proteins are always being degraded while new ones are being made. Gene expression is a continous process that changes based on causes both inside and outside of the cell. Each protein has a specific function. Each protein can have one or many functions, and there are proteins with overlapping functions, different functions in different cells, proteins that form masive complexes with other proteins, resulting in a variety of functions, etc. In addition, the expression level of the gene is not controlled by the gene itself, it is controlled by other proteins. So proteins that are encoded by genes on an entirely different chromosome can affect the expression of the eye color pigment genes. This is what makes genetics so complex.
*NOTE - Stanford has a great online exhibit of DNA on their homepage. It is VERY COOL!!
The Basics of Eye Color
Eye color refers to the pigment that is in the iris of each eye. The gene expression in the eyes determines which pigments (proteins) are made, how much is made, and where in the iris they are stored. Remember these proteins are constantly being made and destroyed, and the gene expression is being affected by causes inside and outside of the cell, such as sudden mutation, or hormone production.
Eye Color Genetics
It is known a variety of genes influence eye color, but the major contributor is the OCA2 gene, which produces the protein pigment melanin. This gene expression explains the basic blue and brown eye color inheritance. Remember you have two copies of this gene (one from mom and one from dad). Both genes are present, but in blue eyes they aren't making much (or any) pigment. One good copy of this gene making pigment in high levels will give a person brown eyes. These genes could also show a variety of expression levels, differing between individuals or within the same individual at different times (which is why eye color can change).
Pigments other than melanin contribute to eye color, and making of these pigments is controlled by other genes. Also, eye color can be affected by the structure of the iris. In the interest of space, I would like to direct you to the Wiki article on eye color if you want additional information. the basis I have provided you here will help you understand their detail. It is really quite an interesting subject!
The QUICK take-home message:
Genes are used as instructions to make protein, such as the pigment melanin.
Gene expression is controlled by a variety of things, including other proteins, hormones and mutation.
The OCA2 gene produces melanin in the iris of the eye. If one or more copies of the gene is producing melanin, the eyes will appear brown. Other genes, other pigments, and the structure of the eye also control eye color.
Another good website for more information on genetics (and specificaly eye color) is run by Stanford's School of Medicine. They have an eye color calculator "for fun", which of course, is a simplification of how it really works in real life.
I am happy to use this forum to answer questions about eye color inheritance. There are a few good resources I can use to help you understand the many exceptions to basic blue-brown eye color inheritance.
Tonya
AKA sunmoonstars
Comments:
Thank you for posting this! So my understanding after reading some of the articles others posted on my thread, was basically correct. It's all about how the genes are "read" or gene expression :)
That stinks I cant use the calculator thingie because my husband was adopted so I don't know his biological parents eye color.. boo
sunshine - you can play with it and try a few variations (just for fun), to see how the results would be affected :) I had to do that since I didn't know my in-law's eyecolor without asking.
Ok, I read through this and my brain hurts. The scientific speach went way, and I mean waaaaay over my head.
My eyes are brown, my hubby's are blue. My oldest son has Dark brown eyes like mine. My youngest son's eyes are hazel (he will be 2 in may) and they appear to change color often.
his parents
Brown and Blue
my moms are Brown, not sure about bio dad as I have never met him.
My Grandmother, my mom's mom, has green eyes.
So where did my son most likely get his green/hazel eyes, and could they just not have completely changed to brown yet?
cool post btw
Very enlightening! Thanks!
Sophie - sorry, I am working on making these posts more user-friendly, so thanks for your feedback.
Yes, your son's eyes may not have changed yet. The geneticists at Stanford explain that here - http://www.thetech.org/genetics/ask.php?id=176 . If they are his permanent color, he most likely has the green eyes as a result of a variety of genes and pigments all working together. In brown eyed people this is hidden by the massive amounts of melanin in the iris.
My dh's eyes seem to change daily too. Stanford explains it here http://www.thetech.org/genetics/ask.php?id=30 but basically, I think that the daily change is more due to how we perceive colors, lighting changes and clothing colors than anything else.
I hope that helps! It really is a complex subject.
Thank you so much for the clarification!!!
Its probably not the wording of your post so much as science always gets jumbled in my head.
My oldests son's eyes didn't fully change till he was about 14 months old.
Jack the youngest also has lighter hair, could it be that since his hair is lighter that his eyes will be lighter as well?
btw, my eyes are Green, Grey with flecks of Gold...my parents and grandparents (with the exception of one with brown/hazel eyes) have beautiful blue eyes. Maybe I should ask my mom about the milkman?!
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I liked that. it also explains to me why some people have bright blue eyes in youth that turn sorta dull gray-blue as they age.
- MythicMMM
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