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The OCA2 gene (oculocutaneous albinism II) is the primary gene controlling brown, hazel, green, and blue eye color in babies. It codes for a protein that helps produce melanin in the iris, the colored ring around the pupil. Variants of OCA2 reduce melanin production, which lightens eye color.
OCA2 accounts for about 74% of the variation in human eye color. It works closely with a neighboring gene called HERC2, which acts as a switch controlling whether OCA2 is turned on or off.
The OCA2 gene codes for the P-protein, which sits in the membrane of melanosomes (the cellular compartments where melanin is produced). The P-protein helps transport substances needed to make melanin.
When OCA2 is fully functional, melanocytes produce abundant brown melanin. This melanin accumulates in the iris of the eye, producing brown or dark eyes.
When OCA2 variants reduce protein function:
The gene is on chromosome 15 at position 15q12-q13.
| Eye color | OCA2 expression level | Approximate global frequency |
|---|---|---|
| Brown / dark brown | High (lots of melanin) | 70-90% globally |
| Hazel | Medium | 5% |
| Green | Low | 2% |
| Blue / grey | Very low | 8-10% |
| Pink/red (albinism) | None (with full mutation) | <1% |
The amount of melanin produced controls the shade. More melanin means darker eyes. Less means lighter eyes.
OCA2's expression is partially controlled by a neighboring gene called HERC2. A specific variant in HERC2, called rs12913832, acts as a switch that turns OCA2 on or off in the iris.
The blue-eye variant (G/G) is recessive. Two copies are needed for blue eyes. One copy (A/G) usually produces hazel or green eyes. Two A copies produce brown.
This is why eye color was once taught as Mendelian: the HERC2 switch behaves like a simple dominant/recessive gene. The full picture involves additional genes that explain green, hazel, and various shades of brown.
For the simplified two-gene model (OCA2 with HERC2 switch):
| Parent 1 OCA2 status | Parent 2 OCA2 status | Most likely baby outcome |
|---|---|---|
| Brown eyes (functional OCA2) | Brown eyes (functional OCA2) | Brown eyes (>90%) |
| Brown eyes | Blue eyes (recessive variant) | Mostly brown, sometimes lighter |
| Brown carrier | Brown carrier | 25% blue, 75% brown |
| Blue eyes | Blue eyes | Mostly blue (95%+) |
| Hazel/green | Hazel/green | Varies, often hazel/green |
For real biological accuracy, you would also need to factor in at least 14 other eye color genes, each making a small contribution. For practical prediction, the OCA2/HERC2 model captures most of what happens.
Two blue-eyed parents are typically both homozygous for the OCA2/HERC2 blue-eye recessive variant. The baby inherits the recessive variant from both parents, producing blue eyes. The rare exceptions (less than 5% of cases) usually involve other genes contributing pigmentation.
This is one of the most reliable eye-color predictions in genetics. If both parents have blue eyes, the baby almost certainly will too.
Both parents can carry the recessive OCA2/HERC2 blue-eye variant without expressing it. They have brown eyes because their dominant allele wins out. If both parents pass their recessive copy to the baby, the baby has two recessive copies and shows blue eyes.
The probability:
This is exactly the kind of probability a Punnett square calculates.
Severe OCA2 mutations cause oculocutaneous albinism type 2 (OCA2), an inherited condition characterized by:
OCA2 albinism is one of the most common forms of albinism, especially in populations of African and African-American ancestry. It is inherited in a recessive pattern, requiring two non-functional copies of the OCA2 gene.
This is also why the gene is named "oculocutaneous albinism" rather than something descriptive of normal eye color. Researchers identified the gene because mutations cause albinism. Only later did they realize variants of the same gene control normal eye color variation.
OCA2 variants are distributed differently across populations:
This distribution reflects the geographic history of how OCA2 variants spread through populations.
While OCA2/HERC2 is the dominant factor, at least 16 genes contribute to eye color. Notable contributors:
Together with OCA2, these explain why some people have hazel eyes (a mix of brown and green), why eye color can shift slightly over a lifetime, and why heterochromia (different colored eyes in one person) occurs.
For predicting baby eye color, our calculator factors in parent and grandparent eye colors to capture multi-generational gene flow. For a visual prediction of overall appearance, the AI baby photo generator at PredictMyBaby reads parents' phenotypes directly.
Many babies are born with blue or grey eyes that change over the first 6-12 months. This is because melanin production in the iris ramps up after birth. By 6-9 months, the eye color is usually settled, though small changes can continue into early childhood.
This developmental timing is controlled by OCA2 expression. The gene starts producing more P-protein in the months after birth, increasing melanin and darkening eyes that were destined to be brown.
If you have a newborn with blue eyes and both parents have brown eyes, the baby's eyes will likely darken over time as OCA2 expression increases.
OCA2 codes for the P-protein, which helps melanocytes produce melanin in the iris of the eye. Higher OCA2 expression produces more melanin and darker eyes. Lower expression produces less melanin and lighter eyes (hazel, green, or blue).
OCA2 is located on chromosome 15 at position 15q12-q13. It sits very close to the HERC2 gene, which controls whether OCA2 is turned on or off in the iris.
OCA2 controls approximately 74% of human eye color variation. It is the single most influential gene for eye color. The remaining variation comes from at least 16 other genes contributing smaller effects.
OCA2 itself is codominant: it produces melanin at levels proportional to the gene copies you have. However, the HERC2 variant that switches OCA2 on or off behaves in a more dominant/recessive way. The blue-eye variant is recessive.
Yes. Both parents can carry the recessive OCA2/HERC2 blue-eye variant without expressing it. If both pass the recessive variant to the baby, the baby has blue eyes even though both parents have brown. This is the standard recessive inheritance pattern.
OCA2 primarily affects eye color, but it has small effects on skin and hair pigmentation in some populations. Mutations causing albinism affect all three (eyes, skin, hair). Normal variation in OCA2 affects mostly eye color.
Want to see what color eyes your baby is most likely to have? Try our free baby eye color calculator for a multi-generation prediction. For a full appearance visualization, the AI baby generator reads both parents' faces and produces a realistic baby prediction.