What you carry at this position in your DNA and what research says about it.
Eye Pigmentation and Health: 10/10 evidence, 25 publications.
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Sample genotype (not yours): C/C
Darker Eyes with Glaucoma Risk
This genotype is strongly associated with brown eyes and darker hair. It carries a higher risk for glaucoma and cataracts, but offers protection against macular degeneration.
What this genotype means: Strongly linked to brown eyes; Higher risk of glaucoma; Lower risk of macular degeneration.
Sample genotype (not yours): C/T
Typical Eye Color and Balanced Risks
This heterozygous genotype typically results in intermediate or dark eye colors. It represents a balanced genetic profile with moderate, intermediate risks for various ocular conditions.
What this genotype means: Associated with hazel, green, or brown eyes; Intermediate risk profile for eye diseases; Moderate UV sensitivity.
Sample genotype (not yours): T/T
Lighter Eyes with Macular Degeneration Risk
This genotype is highly predictive of blue or gray eyes and lighter hair. It is linked to an increased risk of macular degeneration and uveal melanoma, but a lower risk of glaucoma.
What this genotype means: Highly predictive of blue or gray eyes; Increased risk of macular degeneration; Lower risk of glaucoma.
Gene function and biological role
Gene Function: The HERC2 gene encodes a large enzyme that plays a key role in targeting proteins for degradation, but its most famous region is an intron that acts as a genetic switch [1]. This switch functions as an enhancer regulating the neighboring OCA2 gene, which is responsible for producing P-protein [2]. P-protein is essential for the maturation of melanosomes and the synthesis of melanin pigment in the eyes, skin, and hair [3]. When this regulatory region is altered, OCA2 expression is dramatically reduced, resulting in a lack of melanin in the iris [4]. Consequently, HERC2 is recognized as the primary genetic gatekeeper determining blue versus brown eye color in human populations [4].
Variant Impact: The rs1129038 variant is a single nucleotide polymorphism located in the 3 prime untranslated region of the HERC2 gene. It is inherited as part of a highly conserved ancestral haplotype that spans chromosome 15 and is strongly linked to eye color [1]. The T allele is strongly associated with lighter eye colors, such as blue and gray, as well as lighter hair shades [5]. Conversely, the C allele is associated with darker brown eyes and dark hair [4]. Beyond cosmetic traits, this genetic variation alters light sensitivity and tissue vulnerability, influencing the risk of several ocular conditions including macular degeneration and glaucoma [6].
Key Insight: This single genetic spelling change is part of the founder haplotype responsible for nearly all blue eyes in the global population, but it also acts as a biological trade-off that alters susceptibility to different types of degenerative eye diseases.
Location: HERC2. Chromosome 15 · 15q13.1 · 28.1 Mb
Origin Story: The blue-eye haplotype associated with the T allele is believed to have arisen from a single founder mutation in the Near East or Europe around 6,000 to 10,000 years ago, rapidly spreading due to positive selection and sexual selection.
Estimated prevalence by population
Global 36.4%; European 5.7%; African 76.4%; East Asian 99.7%; South Asian 82.7%; Americas 57.2%; Ashkenazi 18.4%; Finnish 1.6%; Middle Eastern 60.7%; Amish 14.2%.
Estimated CC genotype frequency.
Global 29.9%; European 36.3%; African 22.0%; East Asian 0.3%; South Asian 16.5%; Americas 36.9%; Ashkenazi 49.0%; Finnish 22.1%; Middle Eastern 34.4%; Amish 47.0%.
Estimated CT genotype frequency.
Global 33.6%; European 58.0%; African 1.6%; East Asian < 0.1%; South Asian 0.8%; Americas 5.9%; Ashkenazi 32.6%; Finnish 76.3%; Middle Eastern 4.9%; Amish 38.8%.
Estimated TT genotype frequency.
Showing effects for C/C genotype
Organ Systems
Pigmentation & Appearance
Eye Color. Evidence: 9/10. Source: PMID 18172690. Darker (Brown).
Hair Color. Evidence: 10/10. Source: PMID 30166351. Darker Hair.
Vision & Eye Health
Macular Degeneration. Evidence: 9/10. Source: PMID 36917350. Typical Risk.
Open-Angle Glaucoma. Evidence: 6/10. Source: PMID 37386247. Increased Risk.
Cataract. Evidence: 8/10. Source: PMID 34594039. Increased Risk.
Cancer & Oncology
Skin Cancer
Uveal Melanoma. Evidence: 4/10. Source: PMID 34424336. Typical Risk.
Showing effects for C/T genotype
Eye Color. Evidence: 9/10. Source: PMID 18172690. Intermediate/Dark.
Hair Color. Evidence: 10/10. Source: PMID 30166351. Intermediate.
Macular Degeneration. Evidence: 9/10. Source: PMID 36917350. Slightly Increased.
Open-Angle Glaucoma. Evidence: 6/10. Source: PMID 37386247. Slightly Increased.
Cataract. Evidence: 8/10. Source: PMID 34594039. Slightly Increased.
Uveal Melanoma. Evidence: 4/10. Source: PMID 34424336. Slightly Increased.
Showing effects for T/T genotype
Eye Color. Evidence: 9/10. Source: PMID 18172690. Lighter (Blue/Gray).
Hair Color. Evidence: 10/10. Source: PMID 30166351. Lighter Hair.
Macular Degeneration. Evidence: 9/10. Source: PMID 36917350. Increased Risk.
Open-Angle Glaucoma. Evidence: 6/10. Source: PMID 37386247. Typical Risk.
Cataract. Evidence: 8/10. Source: PMID 34594039. Typical Risk.
Uveal Melanoma. Evidence: 4/10. Source: PMID 34424336. ~1.79x Increased Risk.
What this genotype means for the people who carry it
Sample genotype: CC (Homozygous)
Having two copies of the C allele means the genetic switch for eye pigmentation remains fully active [1]. This results in high levels of melanin in the iris, giving rise to brown eyes and providing natural protection against ultraviolet radiation [2]. Because of this protective pigment, there is a significantly lower risk of developing uveal melanoma, a rare cancer of the eye [3]. Additionally, this genotype is associated with a lower risk of age-related macular degeneration [4]. However, large-scale genetic studies show that the C allele is linked to an increased susceptibility to open-angle glaucoma and cataracts [5]. Regular comprehensive eye exams are beneficial to monitor intraocular pressure and lens clarity over time.
Strongly linked to brown eyes; Higher risk of glaucoma; Lower risk of macular degeneration.
Sample genotype: CT (Heterozygous)
Carrying one copy of each allele usually leads to intermediate eye colors, such as hazel or green, or sometimes brown depending on other genetic modifiers [1]. The presence of one C allele provides moderate melanin production, offering some protection against ultraviolet light compared to light-eyed individuals [2]. Consequently, the risk for uveal melanoma and age-related macular degeneration is only slightly elevated compared to the baseline [3]. At the same time, the presence of the T allele slightly mitigates the higher risk of glaucoma and cataracts associated with the C/C genotype [4]. This intermediate status means that overall ocular risks are relatively balanced. Maintaining standard eye care and wearing UV-protective sunglasses outdoors remains a sensible practice.
Associated with hazel, green, or brown eyes; Intermediate risk profile for eye diseases; Moderate UV sensitivity.
Sample genotype: TT (Homozygous)
Inheriting two copies of the T allele downregulates the expression of the nearby OCA2 gene, drastically reducing melanin in the iris [1]. This lack of pigment allows light to scatter, creating the appearance of blue or gray eyes [2]. Because lighter eyes allow more light to penetrate, this genotype is associated with a higher susceptibility to age-related macular degeneration [3]. It also carries an increased risk of uveal melanoma, a rare eye cancer [4]. On the positive side, studies indicate that this genotype is protective against cataracts and open-angle glaucoma [5]. Protecting the eyes from UV radiation with sunglasses is highly recommended to mitigate light-sensitive risks.
Highly predictive of blue or gray eyes; Increased risk of macular degeneration; Lower risk of glaucoma.
Variants with shared genetic architecture
rs12913832 · HERC2 Gene · Chr 15 · Eye Color and Skin Cancer
rs1667394 · HERC2 Gene · Chr 15 · Eye Color
rs916977 · HERC2 Gene · Chr 15 · Eye Color
Human eye colour and HERC2, OCA2 and MATP.
Genetic determinants of hair and eye colours in the Scottish and Danish populations.
Different Pigmentation Risk Loci for High-Risk Monosomy 3 and Low-Risk Disomy 3 Uveal Melanomas.
Diversity and scale: Genetic architecture of 2068 traits in the VA Million Veteran Program.
Content updated August 2026.
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