The Genetics Behind Eye Color

The genetics of eye color is a fascinating topic that is commonly inquired about.

Eye color is determined by your genetics, but it can be difficult to discern who gets what eye color, and for what reason. 

Read on to learn about how eye color is determined, its genetic and hereditary aspects, and what each color means.

What Determines Eye Color?

You might be surprised to learn that there is no such thing as green or blue pigment in the human eye. In fact, all eye colors are made up of levels of brown melanin.

The concentration and location of this melanin determine the color, based also on the reflection of light.

All brown eyes are in fact blue underneath, and blue or green eyes simply indicate the absence of brown pigment and not the presence of blue or green.

In our cells there are 46 chromosomes; divided into 23 pairs. Within each pair, you inherit one chromosome from each parent.

Chromosome 15 plays a large role in determining eye color for each child, and within this chromosome, there are two important genes, called OCA2 and HERC2. 

• The OCA2 gene is responsible for P protein production. The more protein present, the more likely the eyes will be brown. On the other hand, the less P protein present, the more likely the eyes will be blue 
• The presence of the HERC2 gene can affect the levels of protein as well, essentially turning the OCA2 gene on and off 

The genetic information a child gets from his or her parents determines the color of their eyes. 

Is It Genetic?

The eye color of each person is determined by the genetic material they receive from both parents; the presence and levels of the two genes, OCA2 and HERC2. If at least one genetic variation of the HERC2 gene is present, it can reduce the amount of protein or melanin produced.

This then leads to higher chances of lighter eyes like blue, green, or hazel. The color will be determined by the parents’ color, and whether their genes are dominant or recessive.

Is It Hereditary?

In the past, the consensus was that there was one hereditary factor determining eye color. For example, it was believed that if one parent had brown eyes, that gene would be dominant, and the lighter eye gene recessive.

There was an overall consensus that darker colors were more dominant than lighter colors, based on a polarized understanding of dominant and recessive genes.

Thanks to advancements in genetics, we now know that this model is too simplistic and that there are many genetic factors that can predict a child’s eye color.

Can It Be Predicted?

While we cannot predict the eye color a child will have, we can calculate probability.

One way is using a Punnett square. Scientists are able to use this method to plot the genetic information within a grid to gain an understanding of probabilities for any color outcome.

For example, if two parents have brown eyes but carry a blue-eye gene, the grid will indicate that the child will most likely have brown eyes, with a 25% chance of blue eyes. 

What Does Your Eye Color Mean?

Eye color may contain interesting insights into your ancestry and family history. In fact, people with blue eyes may have originated from one singular ancestor some 6,000 years ago.

Here is what you can learn about each color:

Blue eyes: 

• A mutation in the OAC2 gene caused humans to develop blue eyes
• There may be an evolutionary benefit to having blue eyes since the mutation continues, but specific details are still unknown
• Around 8-10% of the world’s population has blue eyes

Green eyes: 

• Green eyes are rare, and only about 2% of the population have them
• There is no green pigmentation present in the eyes. Like blue eyes, their color is due to low levels of brown melanin
• Changes in the light can cause green eyes to appear to change colors

Brown eyes: 

• Originally all humans had brown eyes
• There are many variations of the brown pigment, and it depends on your specific genes
• Brown eyes are more easily protected from the sun, and oftentimes people with brown eyes have darker skin as the two are closely related genetically

Hazel eyes:

• Hazel eyes are most closely related to brown eyes, though only 5% of the world has them
• It can be difficult to define the exact color of hazel eyes since they often have specks of green, brown, and gold present

Conclusion

Eye color is a fascinating subject. Due to the fact that it is based on genetics, it is hard to determine how each gene will behave or determine outcomes.

However, understanding your DNA and family history may provide helpful information and clues.