Someone with brown eyes may be carrying one blue allele and one brown allele, so a brown-eyed mother and a blue-eyed father could give birth to a blue-eyed child. So, to try and clarify things, let’s think about this situation. This is because the generally less dominant blue-eyed trait can be passed along by brown-eyed people until the genes for the lighter eye colour happen to match up, possibly many generations later. Generally though, it’s far more likely for two brown-eyed parents to have a blue-eyed child than for two blue-eyed parents to have a brown-eyed child. How eye colour is inherited is far more complicated than what was thought back in the day. But since they have brown-eyed, green-eyed and blue-eyed children, the most likely possibility is that mum is Bb Gb, meaning she has brown eyes but carries genes for both blue and green eyes. Since mum has brown eyes, she could have any of six different possibilities. Dad can only be bb bb as he has blue eyes. The possible gene combinations that can give you brown, green, or blue eyes are shown in the chart.īack to the green or blue-eyed children. Brown is dominant over green, so if you have a B version of gene 1 and a G version of gene 2, you will have brown eyes. Green eyes can be GG, or Gb, while blue eyes are bb. So brown eyes are either Bb or BB and blue eyes are bb.įor gene 2, there are two possibilities, green or blue. Geneticists represent the different versions of the eye colour gene as B for brown and b for blue (the capital letter is the dominant, the lowercase, recessive). Dominant means that if at least 1 of your two copies is brown (Bb), then you will have brown eyes. The brown version of gene 1 is dominant over the blue one. Let’s look at why a blue-eyed parent (dad) and a brown-eyed parent (mum) and can have brown, green, and blue-eyed children.įor gene 1, OCA2, there are two possibilities: brown or blue. ( This model is too simple to explain a lot of things, but it will suit our purposes.) Why are our kids’ eyes different colours?

For each gene, we inherit two copies, one from our mother and one from our father. In the simplest models of eye colour, there are two genes involved. There is evidence that up to 16 genes can influence eye colour the two most important genes are OCA2 and HERC2. This is what makes it possible for two blue-eyed parents to have brown-eyed children. But modern science has shown that eye colour is not at all that simple.Įye colour is a polygenic trait it is determined by multiple genes and the interactions between them. It was originally thought that eye colour was a simple Mendelian trait, that it was determined by a single gene. An increasing proportion of the yellow melanin, in combination with the black melanin, results in shades of colours between brown and blue, including green, grey and hazel.īrown is the most frequent eye colour worldwide. Eye colour comes from a combination of two black and yellow pigments, melanin, in the iris. If you have no melanin in the front part of your iris, you have blue eyes. The human eye comes in many different shades and intricate, unique iris patterns. Why? Well, it’s complicated, but we can start by telling you that what you learnt at school, assuming you are of a certain age, is wrong. It’s rare, but blue-eyed parents having brown-eyed children does happen.

If both parents have blue eyes, the children will have blue eyes. Where’d the green-eyed monster come from?

Hazel eyes