Eye colour is one of the most fascinating — and most misunderstood — aspects of genetics. The simple dominant/recessive model taught in school is an oversimplification. Here is how it actually works.
It's All About Melanin
Eye colour is determined by the amount and type of melanin (pigment) in the iris. Brown eyes have high melanin; blue eyes have very little. Green and hazel eyes fall in between. The depth of the iris also matters — the same amount of melanin creates different appearances depending on iris structure.
Which Genes Are Involved?
| Gene | Chromosome | Effect |
|---|---|---|
| OCA2 | 15 | Major determinant of brown vs blue eye colour |
| HERC2 | 15 | Controls whether OCA2 is switched on |
| SLC24A4 | 14 | Influences blue vs green distinction |
| TYR | 11 | Tyrosinase enzyme — affects melanin production |
| TYRP1 | 9 | Influences brown pigment type |
Can You Predict Your Baby's Eye Colour?
The old dominant/recessive model suggested two blue-eyed parents could only have a blue-eyed child. In reality, because multiple genes are involved, two blue-eyed parents can occasionally have a green or even light brown-eyed child if they carry the right variants in secondary genes.
Why Newborn Eyes Are Often Blue or Grey
Most babies — regardless of eventual eye colour — are born with blue-grey eyes. Melanin production in the iris is low at birth and increases over the first 6–12 months as UV light exposure stimulates melanocytes. By 6 months, true eye colour is usually apparent. By 12 months, it is mostly fixed — though some people continue to have eyes that shift slightly until age 3.
Eye Colour in Singapore
Most babies in Singapore are born to parents with brown eyes, as the OCA2 gene variants associated with brown pigmentation are dominant in East Asian populations. It is very rare for two brown-eyed Chinese, Malay, or Indian parents to have a blue-eyed child — it would require rare recessive variants in both parents.
Tip
If you're curious about your baby's likely eye colour, it's mostly set by 9 months. Significant changes after that age are very unusual in Asian babies.