You may notice a distinct green or hazel sparkle, icy blue intensity, or deep brown warmth when you glance into someone’s eyes. However, have you ever thought about why the colors of our eyes are so captivating?
Our DNA has the solution. One of the most obvious characteristics influenced by genetics is eye color. Although it may appear to be a simple feature inherited from parents, the science underlying eye color is more complex and intriguing than you might think.
In this blog, we will talk about the role of melanin in eye color and eye colors around the world.
The Role of Melanin in Eye Color
Let’s start with melanin, the pigment that gives our skin, hair, and eyes their color, before getting into genes. The distribution and quantity of melanin in the iris, the colored portion of the eye, are the main factors influencing eye color.
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- Brown eyes have a high concentration of melanin, which absorbs more light and makes them appear darker.
- Green or hazel eyes fall somewhere in the middle, with moderate melanin levels and particular light scattering that gives them their distinct tones.
- Blue eyes have much less melanin, which allows more light to scatter, making the eyes appear blue due to the Tyndall effect—a phenomenon similar to why the sky appears blue.
It's Not Just One Gene
Eye color was thought to be a simple Mendelian characteristic governed by a single gene in the early days of genetics. According to the antiquated theory, two blue-eyed parents could only conceive blue-eyed children since brown was dominant and blue was recessive.
However, modern genetics has demonstrated that eye color is polygenic, which means that several genes, rather than just one, affect it.
The two primary genes associated with eye color are:
OCA2 (on chromosome 15)
This gene plays a major role in melanin production, and changes in OCA2 can lead to lower melanin levels, resulting in blue or green eyes.
HERC2 (also on chromosome 15)
For OCA2, this gene functions as a switch. Lighter eyes can result from a particular mutation in the HERC2 gene that lowers OCA2 expression.
Why Blue Eyes Are a Genetic Surprise
It’s among the most amazing things about blue eyes. They might all have a common ancestor, according to scientists. The first blue-eyed person is believed to have been caused by a genetic mutation in the HERC2 gene, which is estimated to have happened in Europe between 6,000 and 10,000 years ago.
This mutation caused the iris to produce less melanin, and the condition was passed down across generations. Therefore, if you have blue eyes, you probably have a distant ancestor who also has blue eyes!
Can Two Brown-Eyed Parents Have a Blue-Eyed Child?
Yes, it’s absolutely possible.
Multiple genes determine eye color; therefore, parents with brown eyes may contain recessive genes for lighter eye colors without displaying them. A child who inherits a gene that decreases melanin from both parents may have blue or green eyes.
This explains why some families, even when the parents seem very similar, have children with varied eye hues.
What About Hazel and Green Eyes?
Green and hazel eyes, which fall between brown and blue on the eye color spectrum, are less common worldwide. Low to moderate melanin levels and a special combination of yellowish pigments and blue light dispersion give green eyes their distinctive color.
Even more variable are hazel eyes. Because of the unequal distribution of melanin across the iris and the existence of both brown and green tones, they frequently give the impression of changing color in response to illumination and environmental factors.
Can Eye Color Change?
Although most people’s eye color is set by age 3, slight changes can occur due to:
- Aging (some eyes lighten or darken over time)
- Injury or trauma
- Medical conditions such as Horner’s syndrome or pigmentary glaucoma
However, dramatic changes in eye color during adulthood should be evaluated by optometrist, as they can sometimes signal underlying issues.
Eye Color Around the World
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- Brown eyes are by far the most common globally, especially in Africa, Asia, and South America.
- Blue eyes are more common in Northern Europe, particularly in countries like Estonia, Finland, and Sweden.
- Green eyes are the rarest natural color, found in about 2% of the world’s population, mostly of European descent.
This global variation is a result of human migration, genetic mixing, and adaptation to different environments over thousands of years.
Conclusion
Your own genetic code is beautifully expressed in the color of your eyes. Your eyes are the result of complex biological activity, from the predominance of melanin to the minute changes in DNA. Even if our eye color may be inherited from our ancestors, human genetics is made all the more fascinating and surprising by the variances and exceptions.
Therefore, keep in mind that behind that color is a complex genetic adventure encoded in your DNA the next time you look into someone’s eyes or the mirror.
Get your eyes checked—schedule a visit with our optometrist, Dr. Jeffrey Porter, and his associates.
Our experienced eye doctors in Crystal Lake and Algonquin, IL, are dedicated to providing exceptional eye checkups to residents of Crystal Lake, Algonquin, Illinois, and surrounding areas.
Walmart Vision Center Crystal Lake, IL
815-477-4053
Walmart Vision Center Algonquin, IL
847-458-5796
