Both my husband and I have brown eyes. Does that guarantee us a dark-eyed child?
No, it doesn't. Two brown-eyed parents can have a blue-eyed baby. In fact, though less common, the reverse is also possible: two blue-eyed parents could get a brown-eyed baby. "The dominance of brown eyes is a familiar lesson from biology class, but eye color is actually determined by many genes," says Kate Garber, PhD, and director of education in the department of human genetics at Emory University School of Medicine. "One gene might say, 'Let's make lots of blue,' and another says, 'Let's add some brown.' It's like layering colors from different crayons." Meanwhile, other genes control the amount of pigment. Thus, more blue pigment could trump less brown, or a variation such as hazel might emerge. It's not so much that genes are dominant and recessive but that they have stronger and lesser effects, says Robin Bennett, a genetic counselor at the University of Washington Medical Genetics Clinic, in Seattle. "Traditionally we thought dominant genes made the product and recessive ones did not. Now we know that sometimes they both do."