The Mystery of Eye Colour

A child's eye colour is an individual process that depends on the traits the child inherits from their parents. These traits are located in chromosomes. In every pair of chromosomes, one chromosome comes from the father and the other from the mother. If a child receives traits for blue eye colour from both their father and mother, the child will have blue eyes. If the child receives traits for brown eye colour from both parents, the child will have brown eyes.

If the child receives a trait for blue and one for brown eye colour, the child will usually have brown eyes. Brown colour produces more pigment and is therefore dominant. But it is not certain that the child will have brown eyes just because one parent has brown eye colour. This is because the parent may carry genes for blue eye colour despite having brown eyes themselves. If the child has brown eyes, the trait of blue eye colour still exists and can be passed on to the next generation.

Melanin pigment

A child's eye colour can also change over time. Some children are born with very dark eyes, blue or gray eyes, which can later change colour to brown or green. The colour depends on the pigment melanin, which is produced in the so-called stromal cells in the coloured part of the eye, the iris. The maturation of melanocytes in combination with stimulation from the sun provides the melanin that then gives colour to the iris. If the cells contain a large amount of pigment, the eyes will become brown or black. If they contain little pigment, they primarily reflect blue light. This can be likened to small molecules in the air making the sky look blue.

The newborn baby has immature melanin cells, but production develops continuously. As the child grows, the cells mature, which causes colour change. This is often seen around 6 months of age. After 8 months, the child has a more defined eye colour, this is known as the iris' true pigmentation.

The final eye colour of your child is determined by the individual "recipe" for melanin in the cells' DNA. In newborn babies, the cells have not started "reading the recipe" yet. The process starts when the child first opens their eyes outside the womb. The length of time the process lasts is individual. In some newborn babies, the eyes change colour quickly, in others, it takes longer. Generally, the process starts when the pigmentation of the iris changes to its final eye colour around 6 to 12 months of age.