Expert: Dana Krempels, Ph.D. - 6/22/2007

Question
I just have a quick question.. my daughter's father has brown eyes and dark brown hair. His whole family has brown eyes.. on my side of the family has mostly blue eyes except my dad he had green eyes they change to blue.. I had blue eyes they change to hazel.. my daughter right now has blueish grey eyes.. I was just wondering if they will change brown or just stay the same.. and other thing.. I had dark blond hair and her dad has dark brown hair.. she right now has dark blonde.. will they change to brown or just go lighter?

Answer
Dear Amanda,

Eye and hair color in humans are both complex traits, each controlled by more than one gene locus.  This means that although we usually think of eyes being "blue" or "brown", there are actually more than 150 possibilities!  Hair color is nearly as complex and variable.  In short, it's very difficult to predict with precision the exact hair and eye color of a child without knowing *all* the genetic input of both parents.  But we can give it a shot.

Let's do eyes first.

The best known eye color gene locus codes for "brown" or "blue," but other genes contribute other pigments (e.g, yellow pigment overlying a "blue" iris will create green), and other genes will control *how much* of each type of pigment is deposited in the iris.  The combination of these genes results in a range of human eye colors.  The pigment cells in the iris also can expand or contract in response to light and mood and even to what a person is wearing, which means that blue eyes can change to green, hazel, grey, etc., depending on circumstances.  But the underlying iris color is still blue (the recessive trait, which is masked by brown).

If you have light-coloried/blue eyes, your side of the genetics equation is simple:  You will donate one blue eyed allele (form of the blue/brown gene locus) to your child.  If you don't have any greenish tinge to your eyes, then you probably lack the pigment deposition genes for melanin or other pigments (carotenoids), so blue is blue.

If the father has brown eyes, but your child has light eyes, that means that the father carries a recessive blue version of that eye color gene, and he passed it along to his daughter.

That means that the father is *heterozygous* for the blue/brown gene:  he has one copy of each.  He has a 50% chance of donating the brown version to a baby, which would mean the baby will have brown eyes, and a 50% chance of donating the blue version, which would mean the baby will have light-colored/blue eyes (as your daughter does).

If the father's family members also have some of the yellow pigment genes "hidden" behind the dark brown, the baby may also develop green, hazel, or any variation as s/he matures.  You don't say how old your daughter is, but if she still has pale colored eyes by the time she's about 8 months old, she'll probably have pale colored eyes for life.

Hair color, like eye color, is controlled by at least two different genes for pigment (one for the brown pigment, melanin, and one for a reddish carotenoid pigment) plus others that control the amount of pigment in the hair shaft, making hair range from dark brown (almost black) to light brown to blonde to reddish brown/blonde, pale red, and dark red.  Whew!

If you have blonde hair with no reddish tinge, then you will probably donate only those recessive alleles to your baby, and those will code for blonde.  But since your husband has dark brown hair, then he again has a 50% chance of donating the dark hair version to the baby (which is dominant, and the baby would have dark brown hair) and 50% chance of donating the blonde allele *if* he has one from either parent.  In this case, a child could have lighter hair, as your daughter does.

As people age, their hair generally becomes darker, especially if they are born with very light hair.  It's not likely that your daughter's hair will get lighter unless she spends a lot of time in the sun or gets hold of a bottle of peroxide.  ;)

I can't see the subtle variations in hair color of everyone involved, and that could complicate matters.  But this is about as simple an answer as one can give with the information at hand.

Hope that helps.

Dana