In general, children inherit their eye color from their parents, the eye colors of the mother and father. Predict your baby's eye color by selecting mom's and dad's eye colors to see your customized baby eye color chart. But inheritance of eye color isn't that simple because it is polygenic. Polygenic means that the trait is influenced not by one gene, but by multiple genes working together. Even if only the one most obvious gene is considered--the one with the most control over brown vs. all other eye colors, there are still a few things to consider.
- The parents' eye colors
- Whether the parents are homozygous or heterozygous for that color
- If the eye colors of the parents are dominant or recessive.
Each person carries two copies of every gene, one copy inherited from mom and one inherited from dad. Homozygous means that the two copies match (for example, maybe both copies are for brown eyes). If someone is heterozygous, it means that the two copies of the gene differ (for example, one for brown and one for non-brown). It's usually impossible to determine by looking at a person's eye color whether she is heterozygous or homozygous.
Dominance of one copy of the gene over the other means that the dominant copy has an effect you can see, in this case you can see that the person has brown eyes, and the effect of the other gene copy is hidden. Brown and maybe green are considered dominant. Thus a brown-eyed person may carry both a brown version and a non-brown version of the gene, and either copy may be passed to his children.
Two brown eyed parents, if both are heterozygous, can have a blue-eyed baby. By these rules it would seem that two blue-eyed parents cannot have a brown-eyed baby, because blue-eyed people are homozygous. However, eye color, as you remember, is polygenic, and those several other genes exert their effects as well. So yes, while it's unusual, it is possible for blue-eyed parents to have a brown-eyed child, as the baby eye color chart shows.