Expert: Dana Krempels, Ph.D. - 5/9/2009

Question
My husband and I both have blue eyes. Mine are clear blue and my husband has a couple of "specs" of brown or hazel but light blue eyes.  Our first 2 boys have blue eyes But our third boy has dark brown eyes. How is this possible.  I get many questions on this and don't know how to answer this question from people.  There is no question of paternity!!

Answer
Dear Kim,

It is possible that either you or your husband is responsible for your son's eyes, in the form of a mutated gene in either egg or sperm.  Brown eyes is considered the "wild type" in humans, and blue eyes is one "mutant" form of this trait.  When a gene mutates from wild type back to a mutant form, this is known as a reversion mutation.

Only one of you--you or your husband--would have had to pass on this reversion to your son, as the brown eye trait is dominant.  The chances of this happening are small, but it's not impossible.

Hope that helps.

Dana