Hazel eyes are a fascinating eye color that often appear to shift between shades of brown, green, and gold. The exact genetics behind hazel eyes have been widely debated, with many believing they are a mixture of brown and green that results in an in-between eye color. In this article, we’ll explore the key question: are hazel eyes genetically green?
The Genetics of Eye Color
To understand what makes hazel eyes hazel, we first need to understand some basics about eye color genetics. The main gene that determines eye color is OCA2, located on chromosome 15. Within OCA2 are specific variations that code for brown, green, and blue eye colors:
| Gene Variation | Eye Color |
|---|---|
| HERC2 allele with no OCA2 mutations | Blue |
| 1 or 2 HERC2 alleles + OCA2 alleles for brown melanin | Brown |
| 1 HERC2 allele + OCA2 alleles for green melanin | Green |
As you can see, green eyes are produced when there is one HERC2 allele paired with OCA2 alleles that code for green melanin production.
The other main gene involved is SLC24A4, which codes for melanin and also helps determine eye color. Variations in this gene are associated with green and hazel eyes.
What Makes Hazel Eyes Hazel?
Hazel eyes arise when there is a combination of HERC2 and OCA2 alleles that code for both brown and green melanin. Essentially, hazel is a blending of brown and green genetics.
Most hazel eyes have an inner brown or gold ring around the pupil, with an outer green/gold/brown ring around that. The brown tones come from the OCA2 brown alleles, while the green hues are produced by the OCA2 green alleles.
The exact distribution of melanin is unique in each person and accounts for the spectrum of hazel shades. Some hazel eyes appear more brown overall, while others lean green. The ratio of brown to green melanin determines where a hazel eye falls on that spectrum.
Are Hazel Eyes More Green or Brown?
While hazel eyes are a mix of green and brown, researchers have found that the green alleles typically appear to be more influential in hazel eyes:
- One study found that people with hazel eyes had one HERC2 allele and OCA2 alleles associated with green eyes.
- Multiple studies conclude that hazel eyes are genetically closer to green than brown eyes.
- Hazel eyes most likely arise when brown eye genetics mix with strong green genetic components, rather than vice versa.
Therefore, while hazel eyes are a combination, the green influence tends to be stronger than the brown when it comes to the genetics behind hazel eyes.
The Role of Rayleigh Scattering
One factor that makes hazel eyes appear greener is a phenomenon called Rayleigh scattering. This is when shorter wavelengths of light are scattered more easily than longer wavelengths.
Blue and green light have shorter wavelengths than red and brown. Because of Rayleigh scattering, the yellows/browns of hazel eyes are masked, while the greens stand out more vibrantly.
This makes hazel eyes perceptually “greener” than their actual genetic makeup. The scattering effect exaggerates the greenness that comes from the underlying OCA2 genetics.
Hazel Eyes Over Time
Another key aspect of hazel eyes is that they can appear to change color over time. Hazel eyes often appear more brown/gold in childhood but become greener with age.
Again, Rayleigh scattering is at play. As the eye’s collagen fibers loosen with age, this enhances the Rayleigh effect and increases the scattering of brown wavelengths.
In reality, the eye’s genetic makeup is not changing. But the visible color shifts towards green as the Rayleigh effect becomes more pronounced with age.
The Interplay of Genetics and Environment
In summary, hazel eyes arise from a genetic interplay of green and brown eye color alleles. The green alleles play a stronger role than brown in terms of genetic determination.
However, factors like Rayleigh scattering also influence the outward color of hazel eyes. This environmental influence makes hazel eyes appear subjectively greener than their actual genetic makeup.
So in the end, hazel eyes are not genetically fully green. But the green genetic components tend to be stronger, and the environment of the eye further enhances the greenness.
Conclusion
Hazel eyes are an intriguing mix of brown and green genetics. While they are not genetically fully green, research shows the green alleles play a bigger role than brown in producing hazel eyes.
The greens in hazel eyes also pop more, due to Rayleigh scattering enhancing those wavelengths of light. All combined, this gives hazel eyes a perceptual greenness that goes beyond the underlying genetics. But there are still brown genetic components involved that make hazel a true blending of two eye colors.
So in summary: hazel eyes are not genetically fully green, but do tend to be more strongly associated with green alleles and exhibit more visual greenness than their genetic makeup would suggest. Their unique beauty arises from a complex interplay of genetics and physics!
