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Three most recent questions: 2009-11-19 2009-11-05 Although we can't publish all of the questions we receive, we do our best to share our insights on these issues. If you'd like us to consider a question you have about genetics, please fill out the question form.
Ask a Geneticist by Dr. Barry Starr, Stanford University Why do I have blue-eyes? I am an African-American. I am 37 now, it's always been a shock to many. I was born with natural blue-eyes. I am not light skinned at all; I am a brown skinned woman. People are amazed that they are blue just like how white people eyes are. I have a 15 year old and he has one total blue-eye, (the right eye) and the other eye is half brown and blue, weird right? -An undergraduate student from Georgia
 There are a number of reasons why you probably don't have OA. People with OA tend to have very poor eyesight, something you didn't mention in your description. Also, they probably would have tested you for this and told you about it at the Georgia Eye Institute. The final reason is that you are a woman. Like colorblindness or hemophilia, OA happens mostly in men (see the OA link below for more details on why this is). If not OA, then what about the other possibilities? It is possible that there are white relatives on both your mother's and your father's side of the family. You need to have Caucasian relatives on both sides as will hopefully become clear later. It can sometimes take many generations for a trait like blue eyes or straight hair to pop up in the family tree again. The reason it can take a few generations to see something like blue eyes or red hair is that these are both recessive genes. To help understand how this works, let's give an example. Our example simplifies eye color too much (see the reference below for more details on how eye color might really work), but it'll make the same point as a complex example would. Remember that for most genes, you have two copies of each gene that you inherited from your mother and your father. The brown version of the eye color gene (B) is dominant over the recessive blue version (b). Dominant means that if either of your genes is the B version, then you will have brown eyes—blue is recessive to brown's dominance. Genetically speaking, people with brown eyes can either be BB or Bb; people with blue eyes only bb. How could two brown-eyed people have a blue-eyed baby? The most likely way is if both were carriers for blue eyes (Bb). Each parent would contribute a b version of the gene so that the child would be bb and have blue eyes. If a single gene were involved, the chances for a blue-eyed child would be 1 in 4. One of the ways blue eyes can stay "hidden" for a long time is if there are always marriages between Bb (brown eyed carriers of blue eyes) and BB folks. You can only get brown eyes from this mix—the BB parent can only contribute the dominant B gene. The situation is actually even more complicated making it even harder to get blue eyes. There are at least two and probably more eye color genes. All your copies have to be the blue kind to get blue eyes. This makes blue eyes rarer still. What if there are no whites in your background? Another possibility is that a key eye color gene was mutated or changed in you so that you now have blue eyes. These sorts of mutations are rare but it is where all the wonderful variety of people you see around you originally came from. You may be a genetic pioneer! More Information |
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