You would think that if two parents have brown eyes that their children would also have brown eyes but this does not always occur! Genes determine eye color. It is more likely that the children will have brown eyes if the parents are brown eyed but they could also have hazel, green or blue eyes!
Genes are subunits of DNA (or deoxyribonucleic acid) and all physical traits of a person are controlled by genes. When a baby is conceived the mother and father pass down their genes to the child. Originally, the genes came from the newly conceived baby’s grandparents, great-grandparents and on it goes. Therefore it is possible, although unlikely that the baby could be born with one of his great grandparent’s green eyes which can seem strange if no one in the immediate family has them.
The science behind eye color is very technical. Simply put, an individual person has two eye color genes which their parents provided them with. In males this is represented as BG, the potential for brown and green eyes. In females this would be BBI the potential for brown and blue. A set of parents could randomly send one of these genes with the sperm or the egg used to create the fetus so the child could have blue, green, brown, hazel or some combination.
There are eye colors that are more dominant than others. If a child has brown and blue eye color genes passed to them it is more likely they will have brown eyes and this is because brown eye genes are dominant over blue eye genes. Recessive and dominant genes also determine vision, hair color, finger/toe length and health conditions amongst other characteristics. Visible characteristics are usually from dominant genes being passed down.
To expand on this, there are several genes that are responsible for eye color. This makes it even trickier to know what eye color your child could have. Each of the eye color genes also controls other aspects of the eye color, for example, how light or dark the eyes are. A child born with brown eyes might have very dark brown eyes, very light brown eyes or any shade of brown in between.
Most babies are born with blue eyes but after a few months and in some cases two years, the baby’s eyes will change to the color they will have in adulthood. Parents therefore may not know what color eyes their child will end up with until they are two years old!
If both parents have brown eyes it is most likely their child will too. If the parents have the same eye color then it is most likely the child will have the same eye color. If the parents have different eye colors then it is most likely the child will inherit the dominant eye color. It is possible that the child will have an eye color given by a recessive gene so could have different color eyes to his parents.