|MadSci Network: Genetics|
First, let me apologize for the long delay in answering your question. Unfortunately, things got lost in the shuffle, which we try to avoid, but sometimes it happens. I hope you are still interested in the answer to your question! Eye color is a very complicated and interesting phenomenon. Many people know that brown eyes are "dominant" over blue eyes. In other words, you only need one copy of a "brown eyed gene" to have brown (dark) eyes, but to have blue (light) eyes you need two copies of the "blue" version of the gene. For a long time, it was thought to be that simple. Unfortunately, it is actually quite a bit more complicated, and frankly, we don't understand in detail all the things that affect eye color. The simplest thing known to affect eye color is the production of a pigment called melanin in the iris of the eye. This is the same pigment that makes your skin brown. Some people have genes that give higher melanin production in the eye, resulting in dark eyes, and since you only need one copy of the high-producing gene to get pigment production, dark eyes are "dominant". These same people tend to have dark skin as well, as is common experience. However, it is very possible to have black individuals with blue eyes, and all sorts of other interesting combinations. So melanin production in the iris doesn't seem to be absolutely linked to skin color. Further, it is clear that many more subtle features of the eye affect its apparent color, beyond just the level of pigment. Specifically, the architecture of the iris affects the way it reflects light, and thus the color that it appears. Interestingly, this is similar to the way that bird feathers appear so many different colors - they often do not contain colored pigment, but simply look colored by how they reflect the light. For the eye, we don't know exactly what all these factors are, nor how they are inherited. We call such traits "multi-factorial". But WHY do we have different colored eyes - what purpose does eye color serve? The simple answer is none. Even though people continue to try to show a difference in the ability to do certain tasks based on eye color, there is really no good reason to think that the color of your eye affects any aspect of vision. The purpose of melanin in general is to protect the skin from damaging UV light, and presumably this happens in the iris too. However, people with blue eyes don't seem to have a problem! Finally, it is also true that eye color is like any other trait of appearance. We may not be able to give a specific function, but these traits certainly affect the way other people see us, how they react to us, and ultimately, how likely we are to be able to reproduce and pass on more of our blue-eyed genes to our children! Hope this helps. I also hope I understood correctly that the questioner here was a teacher of grades 4-6, and not a student.
Try the links in the MadSci Library for more information on Genetics.