Expert: Dana Krempels, Ph.D. - 12/11/2007

Question
I have two children that have blue eyes, and I have brown eyes. Their dad has blue eyes. I know that it takes two recessive genes for someone to have blue eyes. I'm wondering if maybe I don't carry the brown eyed gene, even though I'm brown eyed. is that possible?

Answer
Dear Laura,

Although eye color inheritance is turning out to be far more complex than scientists first thought, it's still generally true that there is a gene coding for dark pigmentation of the iris (Brown eyes, usually written in shorthand as "B" to represent that version of the gene) and a different version of the same gene that fails to produce dark pigmentation in the iris (blue eyes, abbreviated "b").

Every person has two copies of each gene, including the B/b gene.  So the possible combinations are BB, Bb, and bb.

The brown version is considered to be dominant to the blue version, meaning that a person needs to have only one copy of B to mask the expression of b.  Your husband's genotype with respect to this gene must be bb if he has blue eyes.  You, on the other hand, could be either BB or Bb.

Since you have brown eyes, but also have blue-eyed children, it's clear that your genotype is Bb, and that each of your children inherited a "b" from dad (the only thing he could give them) and also a "b" from you.  Each child *could* have inherited a "B" from you, but since there's a 50/50 chance in each birth that the child will get "b", both your kids had a pretty large chance of inheriting blue eyes.

Hope that helps!

Dana