How Identical Twins Can Have Different Eye Colors
Identical twins develop from a single fertilized egg and share nearly the same DNA. Despite this, they can have different eye colors. This occurs when genetic changes or early developmental events affect melanin production in one twin more than the other.
What Is Heterochromia in Twins
Heterochromia means having two different colored irises. In identical twins, it can appear as one twin having two different colors or each twin having a distinct color. The condition results from uneven distribution of melanin during eye development. It is usually harmless and present from birth.
Genetic and Environmental Factors
Eye color is controlled by several genes that regulate melanin. Small genetic differences, even within identical twins, can change how much pigment the iris makes. Rarely, a genetic change or injury early in development can lead to different eye colors. For more on the genetics of eye color, see this overview from the National Library of Medicine.
