Hair Colour Genetics Calculator

Predict the probability of your child's hair color based on parental phenotypes and genetic carriers.

How Hair Colour Genetics Work

Hair color is a complex polygenic trait primarily determined by the amount and type of melanin in the hair shaft. While dozens of genes are involved, the most significant are the MC1R gene (which dictates red hair) and the OCA2/HERC2 complex (associated with brown vs. blonde levels).

In our hair colour genetics calculator, we simplify this using the classic Mendelian model which focuses on two types of melanin:

• Eumelanin: High levels result in brown or black hair. Low levels result in blonde hair.
• Pheomelanin: High levels produce red hair. This gene is typically recessive.

Dominant vs. Recessive Alleles

Brown hair is considered a dominant trait. This means if one parent passes down a "Brown" gene and the other passes a "Blonde" gene, the child will likely have brown hair but will "carry" the blonde gene. For a child to have blonde or red hair, they generally need to inherit the recessive alleles from both parents.

Example Scenario:

If both parents have brown hair but both carry the blonde gene (because they each have a blonde parent), there is a 25% chance their child will be born with blonde hair, despite neither parent showing it.

Why Red Hair is Rare

Red hair is caused by mutations in the MC1R gene. It is a recessive trait, meaning both parents must be carriers for a child to have a chance of being a redhead. Even if two brown-haired parents are both carriers of the red gene, the probability is usually only 25%.

Limitations of the Calculator

Genetics is not always as simple as a Punnett square. Factors such as incomplete dominance and polygenic inheritance mean that hair can come in various shades (strawberry blonde, auburn, etc.) and can change color as a person ages. This calculator provides an estimate based on the most common genetic pathways.

Genetic Insight: