How to Calculate the Probability of a Baby's Eye Color

By Michelle Johnson
Parents often wonder what color of eyes their baby will have.
Parents often wonder what color of eyes their baby will have.

Researchers have studied eye color for more than a century, and throughout most of that time, they believed eye color followed simple Mendelian genetic rules. Brown eyes were dominant, blue eyes recessive, and thus if both parents had blue eyes, their children's eye color would inevitably match the parents'. But scientists have come to realize that eye color is a polygenic trait, which means more than one gene influences it. While it is possible to estimate the probability of a baby having a particular eye color, enough factors influence this trait that the precise shade of eyes a baby will have is one mystery that won't be solved until after a baby's birth.

Determine the eye color of yourself, your mate and both of your sets of parents. While a baby will not necessarily have the same color of eyes as his parents or grandparents, their genes provide the most direct influence on his eye color.

Find out the eye colors of you and your mate's siblings. Sibling eye colors provide clues about possible recessive genes carried in your family trees. Brown-eyed parents with green- or blue-eyed siblings may carry genes for the lighter eye colors that their children could inherit.

Identify whether you or your mate comes from a population where the genes for a particular eye color are more common. In most human populations brown eyes are the norm. Children with African or Asian ancestry, for instance, will most likely have brown eyes. Eye colors other than brown only appear frequently in white populations, and in those populations may even be the most common colors. A 2004 study in "Preventative Medicine" found that 89 percent of Icelandic women and 87 percent of Icelandic men had either blue or green eyes.

Plug your family's eye colors into an online baby eye calculator, like the one at the Tech Museum. This calculator provides an oversimplified model for predicting a baby's eye color since it assumes only three eye colors exist, only two genes influence eye color and everyone using the calculator shares an equal likelihood of producing children with brown, blue or green eyes. Despite these drawbacks, the calculator can provide a rough idea of how likely your baby is to have a particular eye color.

Tip

Many babies are born with blue eyes because pigment in the iris hasn't developed yet. But after birth, light stimulates the production of melanin, and baby's eyes may start changing. You will likely have a good idea of what color your baby's eyes be when she reaches 6 to 9 months of age.

About the Author

Based in southern Idaho, Michelle Johnson started writing in 1991. Her work has been published in the science fiction and fantasy journal, "Extrapolation." Johnson holds a Bachelor of Arts in creative writing and a Master of Arts in fantasy literature, both from Hofstra University in New York.