Expert: John Locke - 5/20/2007

Question
My sons partner is half aboriginal with an olive complexion and brown eyes. He has ginger hair and green eyes. The baby has ginger hair and at present blue eyes with very fair skin. Is ginger hair dominant ??

Answer
Thank you for using AllExperts, and I'd be happy to answer your question.

Hair color in humans is not well-defined genetically, at least compared to human eye color and skin color, for which we have now have a pretty good understanding. The most popular, current hypothesis (though this idea is not yet widely accepted or proven) is that hair color is controlled by two gene pairs; one of these codes for brown/blond (where brown is dominant) and the other controls red/not red (where the not red is dominant). The possible genotype/phenotype combinations would be something like this:

Brown/Not Red: Brown hair
Brown/Red: Dark red hair
Blonde/Not Red: Blond hair
Blonde/Red: Lighter red hair

However, other genes have an effect, as well, with the dominant forms leading to darker hair and the recessive forms leading to lighter hair. The naive model proposed above may or may not be exactly correct, but it does express some known facts about human hair color: brown hair is a dominant trait, while red hair is recessive, and the shade of one's hair is controlled separate from their actual hair color. Remarkably, two parents with the same hair color can give birth to a baby with a completely different hair color, and/or a completely different shade of hair color.

In summary, then, the interaction of all these genes is what yields a given hair color in a person. Red hair is not dominant (nor are the many shades of red hair, like ginger), according to what is currently known; the safest thing to be said about this is that hair color is a polygenetic trait, controlled by the interplay of multiple genes in any one person, and even by environmental conditions (consider the popular stories of soldiers coming back from wartime with their hair turned white out of fear).