Eye Colour Genetics Calculator
Choose each parent’s eye colour to estimate the probability of common eye colours in a child. This tool uses a simplified multi-gene model for educational use.
Note: Real eye colour inheritance is polygenic (many genes), so real outcomes may differ from model predictions.
How this eye colour calculator works
Eye colour is influenced by multiple genes that affect melanin production and distribution in the iris. In classic school biology, you often see a simple “brown dominates blue” model. While that model is useful for introduction, modern genetics shows that eye colour is more complex.
This calculator uses a simplified two-locus inheritance framework with weighted genotype assumptions behind each visible eye colour category. It then combines possible parental genotypes and estimates the child’s probabilities for brown, hazel, green, blue, and gray eyes.
Why eye colour inheritance is not strictly simple Mendelian genetics
1) Multiple genes are involved
Genes near OCA2 and HERC2 are major contributors, but not the only ones. Additional genes can alter pigment amount and light scattering in the iris, creating a broad spectrum of colours.
2) Eye colour is a spectrum
Categories such as hazel, amber, gray, and green overlap. Two people can both be called “green-eyed” while having noticeably different pigmentation patterns.
3) Family history matters
Grandparent and extended family genetics can strongly influence outcomes. Two brown-eyed parents can still have a blue-eyed child if both carry relevant recessive variants.
Interpreting your results
- Percentages are probabilities, not guarantees. A 70% result means “more likely,” not certain.
- Lower percentages can still happen. Even rare outcomes occur in real families.
- Use this as an educational estimate. It is not a clinical or diagnostic test.
Example scenarios
Blue + Blue
Usually predicts mostly blue/gray outcomes, with a smaller chance of green depending on assumed hidden variants.
Brown + Blue
Often produces broad distributions because brown-eyed parents may carry recessive alleles and blue-eyed parents can still contribute modifiers.
Hazel + Green
Frequently yields mixed results spanning hazel, green, and occasionally brown or blue in lower proportions.
Limitations of this calculator
This model intentionally simplifies biology. It does not account for all known gene variants, ancestry-specific allele frequencies, developmental colour shifts in infancy, or uncommon pigment conditions. For rigorous genetic prediction, full genomic analysis is required.
FAQ
Can two blue-eyed parents have a brown-eyed child?
In a very strict single-gene model, no. In real genetics, unusual cases can occur due to additional genes, rare variants, misclassification of eye colour, or complex inheritance patterns.
Do babies keep their birth eye colour?
Not always. Infant eye colour can change during the first months or years as melanin production increases.
Is green rarer than blue?
Globally, yes—green eyes are generally less common than blue eyes, though prevalence differs by region and ancestry.