What is it about a newborn baby’s bright blue eyes that makes our hearts melt? Even if both mom and dad have brown eyes, and the baby itself ends up with brown eyes, they are most likely born with clear, blue irises. Have you ever wondered why?
We all inherit eye color from our parents. Melanin, a protein molecule that determines the colors of our hair, skin and eyes, is coded into a variety of genes. Melanin does not generally settle fully onto the iris of a newborn baby for 6 – 12 months. The color of a child’s iris is usually stable by about six months, but can darken for up to three years.
Production of melanin increases dramatically during the first year. A large amount of this protein will yield dark brown or black eyes; a small amount will give the child green, gray, or light brown eyes; and blue or light gray eyes are a result of very little melanin. Since eye color is a polygenic trait, the actual number of genes that contribute to its color are unknown. Scientists have recently found it possible to predict the likelihood of brown eyes versus blue eyes with up to 90% accuracy. Green eyes are the least common eye color world wide. Predicting this color and its variations (light green, hazel) is still very difficult.
Heterochromia is a condition that occurs when there is an uneven melanin content across the eyes. This may not be initially apparent, but as the protein settles on the irises, the distribution may cause one eye to be a different color than the other. This condition can vary from a slight change in shade to a total color difference, such as blue and green. It occurs infrequently in humans, but can be common among other species like dogs and cats.
Variations in eye color have no effect on your child’s vision. But keep an eye on their eyes throughout the first few years of life … you never know what changes you’ll see!