The study of genetics gives mankind insight on who we are, why we look the way we do, and why we are predisposed to certain diseases, actions, and temperament. Our genes make us who we are, each of individual and unique. Genes and genetics tell us how tall we will be, what color our hair will turn out as we get older, whether we are thin or heavy, look more like or dad, and what color our eyes are.
Eye color is actually determined by two genes and surprisingly enough, only people of European descent actually have different eye colors. Natives to other regions such as South America, Africa, and the Middle East tend to all have brown eyes unless there is a European somewhere in the family tree. The gene for brown eyes is dominant over every other color unless you get that right genetic sequence to have another color, such as blue which is actually the rarest eye color of all.Geneticists use a chart called a Punnett square matrix to determine the many different possibilities of eye color a person can have. Every person has two genes that determine eye color and each of these genes are separated into two alleles – one dominant and one recessive. That means it take four different pieces of genetic material to determine what color eyes a person is going to have. The four parts are labeled ‘B’ for the dominant brown eye color and ‘b’ for the recessive blue with ‘G’ for the dominant green/hazel eye color and ‘g’ for lighter shades of the green/hazel variation.
Every person has a set of two genes that determine eye color from their mother and two genes that determine eye color from their father. This means that the mother will provide four different gene combinations and the father will provide four different gene combinations. When put into a Punnett square, geneticists get sixteen different eye color possibilities for a person. The dominant brown color – ‘B’ – will always be dominant over the dominant ‘G’ for green/hazel eyes. In turn the ‘G’ will always be dominant over the two recessive genes ‘b’ and ‘g’. Out of 16 different eye color possibilities, 12 will be brown, 3 will be a variation of green/hazel, and 1 will be blue.Of course, this is the most basic explanation for how genetics determines eye color.
There are other variables that can be added to this explanation that determines the exact shade of the eyes based on how much black or yellow melonin – a pigment – is actually in your eyes. People with no melonin in their eyes whose genetics give them blue eyes tend to have very light blue to grey eyes. The more melonin in the eyes, the darker they are. More yellow melonin makes your green eyes greener. More black melonin makes your brown eyes browner.
Because of the way genetics works – which is clearly displayed by a Punnett square for the best visual representation – blue eyed parents can have brown eyed children and vice versa. It all depends on which gene happens to be the dominate one when the egg and sperm meet and become one.