rs1800407 — OCA2 Arg419Gln

Eye color modifier gene influencing green and hazel eye color through melanosome pH regulation

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The Green-Eyed Gene — How a Single Amino Acid Shapes Eye Color

Your eyes get their color from melanin, the same pigment that determines skin tone. But eye color isn't just about how much melanin you make—it's also about how efficiently your cells can package it11 how efficiently your cells can package it
Melanin is produced in specialized organelles called melanosomes within melanocytes, and the efficiency of this process depends on precise pH regulation. The OCA2 gene encodes the P protein, a melanosomal transporter that regulates the pH environment where melanin is synthesized22 regulates the pH environment where melanin is synthesized
The P protein is a chloride channel that shifts melanosomal pH from acidic to neutral, which is essential for tyrosinase enzyme activity. When this system works at full capacity, you get deeply pigmented brown eyes. When a variant reduces its efficiency, the result can be lighter shades—including the distinctive green and hazel hues.

rs1800407 is one such variant. This SNP changes a single amino acid in the P protein (arginine to glutamine at position 419), creating a hypomorphic version33 hypomorphic version
A hypomorphic allele produces a partially functional protein—not completely broken, but less efficient than normal that reduces melanin production in the iris. Unlike the famous HERC2 rs12913832 variant44 HERC2 rs12913832 variant
The HERC2 rs12913832 SNP is the primary determinant of blue vs. brown eyes in Europeans, but rs1800407 in OCA2 acts as a penetrance modifier that primarily controls blue versus brown eyes, rs1800407 is the strongest genetic predictor of intermediate eye colors—green, hazel, and light brown.

The Mechanism

The OCA2 gene sits on chromosome 15 and encodes an 838-amino-acid transmembrane protein localized to melanosomes. The P protein functions as a chloride-selective anion channel55 chloride-selective anion channel
OCA2-mediated chloride efflux from the melanosome lumen reduces proton pump activity, raising organellar pH that modulates the pH of these pigment-producing organelles. Early-stage melanosomes are highly acidic (pH < 6.0), but tyrosinase66 tyrosinase
the rate-limiting enzyme in melanin synthesis | is inactive below pH 6.0. To produce melanin, the melanosome must neutralize its pH—and that's where OCA2 comes in.

By transporting chloride ions out of the melanosome, the P protein counterbalances proton pumps and shifts pH toward neutral. This creates the optimal environment for tyrosinase to convert tyrosine into melanin. The Arg419Gln substitution77 Arg419Gln substitution
rs1800407 changes CGG (arginine) to CAG (glutamine) in exon 13 reduces the efficiency of this chloride transport, resulting in a more acidic melanosomal environment and reduced melanin synthesis.

Importantly, rs1800407 doesn't act alone. HERC2 rs12913832 acts as an enhancer that determines whether OCA2 is expressed at all, while rs1800407 determines how efficiently the protein works once it's made.

The Evidence

Andersen et al. (2016)88 Andersen et al. (2016)
Importance of nonsynonymous OCA2 variants in human eye color prediction. Mol Genet Genomic Med 4:420-430 identified rs1800407 as one of three nonsynonymous OCA2 variants critical for eye color prediction. In a sample of 1,042 European individuals (Scandinavian, Italian, and Portuguese cohorts), a four-variant haplotype (HERC2 rs12913832 + three OCA2 coding variants including rs1800407) explained 76% of eye color variation (adjusted R² = 0.76).

Branicki et al. (2008)99 Branicki et al. (2008)
Association of polymorphic sites in the OCA2 gene with eye colour using the tree scanning method. Ann Hum Genet 72:184-192 used an evolutionary tree scanning approach to identify rs1800407 as the single strongest OCA2 predictor of eye color variation.

Donnelly et al. (2012)1010 Donnelly et al. (2012)
A global view of the OCA2-HERC2 region and pigmentation. Hum Genet 131:683-696 genotyped 3,432 individuals from 72 populations for 21 SNPs in the OCA2-HERC2 region. The rs1800407 T allele (derived allele) is geographically restricted, reaching frequencies of 0-11% in Europe, 0-9.4% in Southwest Asia, and 0-9.3% in Central Asia, with highest frequencies in Northern Europe. Outside these regions, it's rare (1-4% in some Native American and African American populations, <1% in East Asia and Africa).

There's also evidence linking rs1800407 to melanoma risk. Fernandez et al. (2009)1111 Fernandez et al. (2009)
Pigmentation-related genes and their implication in malignant melanoma susceptibility reported that the rs1800407 variant allele was a significant risk factor for cutaneous malignant melanoma in a Spanish case-control study (OR 1.55, 95% CI 1.04-2.31, p=0.03).

Practical Actions

If you carry the T allele, you likely have lighter eye color (green, hazel, or light brown) and possibly lighter skin tone than your CC counterparts. This has implications for UV protection1212 UV protection
Melanin absorbs and dissipates UV radiation, preventing DNA damage. With less melanin in your skin and eyes, you have reduced natural photoprotection and should prioritize sun safety—especially if you also carry blue-eye alleles at HERC2 rs12913832.

Beyond pigmentation, this variant is a reminder of how tightly regulated biological systems are. Melanosome pH must be precisely controlled to balance competing demands: acidic enough to prevent premature melanin polymerization, but neutral enough for tyrosinase to function. A single amino acid change at position 419 tips this balance, producing not just a different eye color, but a slightly different melanin profile throughout your body.

Interactions

rs1800407 shows strong epistatic interactions with HERC2 rs129138321313 HERC2 rs12913832
A regulatory variant in an enhancer region 21 kb upstream of OCA2 that controls OCA2 gene expression. The HERC2 variant determines how much OCA2 protein is produced, while rs1800407 determines how well that protein functions.

There's also evidence for gene-gene interactions beyond OCA2. Studies have found synergistic interactions between HERC2 rs12913832 and TYRP1 rs14087991414 TYRP1 rs1408799
tyrosinase-related protein 1, another enzyme in the melanin synthesis pathway in determining green eye color. The prediction accuracy for green eyes increases from AUC 0.667 to 0.697 when these interactions are modeled. This suggests that the final eye color phenotype emerges from a network of interacting variants across multiple pigmentation genes.

Genotype Interpretations

What each possible genotype means for this variant.

GG Standard Pigmentation Normal

Normal OCA2 function with efficient melanosome pH regulation

You have two copies of the ancestral G allele, which encodes the standard arginine at position 419 of the P protein. Your melanocytes maintain optimal melanosomal pH for tyrosinase activity, allowing full melanin synthesis capacity. About 85% of people globally carry this genotype, though frequencies vary by ancestry—nearly 100% in sub-Saharan Africa and East Asia, and 80-90% in Europe.

Your eye color is primarily determined by other genetic variants, particularly HERC2 rs12913832. If you also carry the GG genotype there, you likely have brown eyes. If you carry the AA or AG genotypes at HERC2, you likely have blue eyes. The absence of the rs1800407 A allele means you're unlikely to have green or hazel eyes unless other rarer pigmentation variants are influencing your phenotype.

CC Standard Pigmentation Normal

Normal OCA2 function with efficient melanosome pH regulation

You have two copies of the ancestral C allele (corresponding to the plus-strand reference allele), which encodes the standard arginine at position 419 of the P protein. Your melanocytes maintain optimal melanosomal pH for tyrosinase activity, allowing full melanin synthesis capacity. About 85% of people globally carry this genotype, though frequencies vary by ancestry—nearly 100% in sub-Saharan Africa and East Asia, and 80-90% in Europe.

Your eye color is primarily determined by other genetic variants, particularly HERC2 rs12913832. The absence of the rs1800407 T allele means you're unlikely to have green or hazel eyes unless other rarer pigmentation variants are influencing your phenotype.

AG Moderate Modifier Intermediate

One copy of the green-eye variant with intermediate effect on pigmentation

The heterozygous state creates a mixed population of melanosomes: some with fully functional P protein, others with the hypomorphic version. This doesn't produce a simple 50% reduction in function—rather, it shifts the population average toward slightly more acidic melanosomes and moderately reduced tyrosinase efficiency. The resulting phenotype is influenced by other genetic and environmental factors, including overall melanocyte density, tyrosinase activity from other genes, and regulatory elements controlling OCA2 expression.

Research shows that heterozygotes contribute significantly to the spectrum of intermediate eye colors. While homozygous AA individuals have the strongest effect, AG genotypes still show measurable impacts on eye color prediction models, improving accuracy by 3-7% when included alongside HERC2 variants.

CT Moderate Modifier Intermediate

One copy of the green-eye variant with intermediate effect on pigmentation

The heterozygous state creates a mixed population of melanosomes: some with fully functional P protein, others with the hypomorphic version. This doesn't produce a simple 50% reduction in function—rather, it shifts the population average toward slightly more acidic melanosomes and moderately reduced tyrosinase efficiency. The resulting phenotype is influenced by other genetic and environmental factors, including overall melanocyte density, tyrosinase activity from other genes, and regulatory elements controlling OCA2 expression.

Research shows that heterozygotes contribute significantly to the spectrum of intermediate eye colors. While homozygous TT individuals have the strongest effect, CT genotypes still show measurable impacts on eye color prediction models.

AA Green-Eye Variant Reduced

Reduced OCA2 function strongly associated with green and hazel eye color

The AA genotype produces melanosomes where chloride transport is consistently impaired, shifting the entire population of pigment organelles toward a more acidic pH. This reduces tyrosinase activity across all melanocytes, not just in the iris. The result is a distinctive phenotype: green or hazel eyes (when combined with reduced OCA2 expression from HERC2 variants), and often lighter skin, freckling, and increased sun sensitivity.

The AA genotype has been under positive selection in Northern Europe, where reduced pigmentation may have been advantageous for vitamin D synthesis at high latitudes with low UV exposure. Long-range haplotype tests show signatures of recent selection, consistent with the allele rising rapidly in frequency over the past 5,000-10,000 years. Interestingly, this is a different evolutionary solution than the one in East Asia, where lighter skin evolved via a different variant (rs1800414, His615Arg) in the same gene—an example of convergent evolution.

TT Green-Eye Variant Reduced

Reduced OCA2 function strongly associated with green and hazel eye color

The TT genotype produces melanosomes where chloride transport is consistently impaired, shifting the entire population of pigment organelles toward a more acidic pH. This reduces tyrosinase activity across all melanocytes, not just in the iris. The result is a distinctive phenotype: green or hazel eyes (when combined with reduced OCA2 expression from HERC2 variants), and often lighter skin, freckling, and increased sun sensitivity.