When the pupil size changes, the pigments in the iris compress or spread apart, changing the eye colour a bit.Ĭertain emotions also can change both pupil size and iris colour. The pupil also shrinks when you focus on near objects, such as a book you are reading. The pupil enlarges in dimmer lighting and grows smaller in brighter lighting. The iris is a muscle that expands and contracts to control pupil size. If you notice an unusual appearance to your eye colour, don't wait to see your eye doctor. Other causes can be inflammation, freckle (diffuse nevus) of the iris and Horner's syndrome. Usually this condition - called heterochromia - is caused by faulty developmental pigment transport, local trauma either in the womb or shortly after birth or a benign genetic disorder. Some children are born with irises that don't match in colour. However, a scenario in which one parent has brown eyes and the other has blue eyes doesn't automatically produce a brown-eyed child. The darker colours tend to dominate, so brown tends to win out over green, and green tends to win out over blue. But if both parents have brown eyes, it's most likely that their children also will have brown eyes. Darkening occurs if melanin, a brown pigment usually not present at birth, develops with age.Ĭhildren can have completely different eye colours than either of their parents. Most non-Hispanic Caucasian babies are born with blue eyes that can darken in their first three years of life. Each parent has two pairs of genes on each chromosome, and multiple possibilities exist for how this genetic information is expressed in terms of eye colour.Īnd early in life, eye colour can change. But modern science has shown that eye colour is not that simple.Įye colour isn't just a blend of the parents' eye colours, as in mixing paint. Other colours, such as gray, hazel and multiple combinations are not fully understood or explainable at this time.Īt one time, brown eye colour was considered "dominant" and blue eye colour was considered a "recessive" trait. These genes account for the most common colours - green, brown, and blue. Human eye colour originates with three genes, two of which are well understood.
The coloured part of the eye is called the iris, which has pigmentation that determines our eye colour. The influences from each parent aren't known until after the child is born. How a child looks depends on the genetic material each parent contributes to the child.īut the parents' genes can mix and match in many different ways.
Will the child's eyes be black, brown, blue, gray, green, hazel or some combination of colours? Eye colour often is the genetic trait that fascinates parents the most as a child develops.
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