Many parents-to-be spend hours wondering who their baby will take after. Will they have blue eyes like theirs? Or will they have striking green eyes like Great Aunt Jane?
All Caucasian babies are born with blue eyes, regardless of the eye colours of their parents. This is because newborns have not yet started producing the pigment ‘melanin’ which is a dark brown colour in the irises of their eyes. A child’s true eye colour cannot be determined until the age of three.
What determines eye colour?
Eye colour is a physical trait that is determined by the pairing of genes from both parents.
There are three eye colour genes that are known to scientists but only two of these are well understood. They explain the inheritance of brown, green and blue eye colours. However they don’t explain why some children have grey, hazel or varying shades of colour eyes.
Genes are the basic units of heredity; they determine many characteristics about a baby. Genes also come in pairs. ‘Alleles’ are found in genes and determine the appearance of any characteristic. There are two alleles for each trait inherited.
One allele is expressed over the other allele. This is called the dominant allele, while the unexpressed allele is called recessive. With eye colour, the brown allele is always dominant over the green and blue alleles, the green allele is always dominant over the blue allele, and the blue allele is always recessive.
Brown eyes are dominant in humans and in many parts of the world. Over half of the world’s population has them. Blue eye colour is the result of recessive genes.