Why do we have different eye-colours?

Why do we have different eye-colours?

Green? Blue? Maybe brown…? Have you ever wondered why do we have different eye-colours? If you want to know more about it, keep reading little scientist!

The colour…

First of all, little scientist, you should know that there are some main factors which determine our eye-colour:

  • The quantity of melamine (dark pigment) in our eyes.
  • How the light that goes through our iris, spreads in our eye.

That pigment’s colour is genetically inherited, which means that it depends on our family’s eye colours. Every cell in our body contains genetic information in its core as well as 46 chromosomes, divided into 23 pairs. These chromosomes are also inherited (middle from our dad and another one from our mum) and contain the information that will determine our physical appearance. That is why you are so similar to your parents, little scientist!

What exactly is a Chromosome?

A chromosome is a DNA sequence compounded by some gens that determine our characteristics. We all have different forms of the same gen, the alleles, each of them inherited from dad and mum. Consequently, the shown characteristic will be determined by the interaction between these gens. How is the interaction between them? There two types of alleles: recessive alleles, which only appeared when there is another similar allele; and the dominant alleles, which always appears. This all means that not all of our parents’ characteristics will be inherited!

Our eye-colour…

Once you know that, notice that blue eyes are normally consequence of recessive alleles, while brown eyes are consequence of dominant alleles, which means that even though some of our parents had blue eyes, if the other doesn’t, we won’t probably have blue in our eyes. However, if our grandparents had blue eyes, we could inherit their recessive alleles to have blue eyes although one of our parents doesn’t!

Who do your eyes-colour match with, little scientist? Parents or grandparents?


  • Babies usually have bright colour since their production of melamine is very low.
  • The Heterochromia is a rare anomaly which is produced during the iris development and people who suffer it have each colour with a different colour.
  • Around the 8% of the World’s population have blue eyes, while just the 2% have green eyes!
  • In Central and North Europe, people normally have blue eyes.

And you…where are your from and what is the most common eye-colour there? Check your family eye-colours and discover why you have that colour in your eyes! Keep paying attention to our blog if you want to discover more things about science, little scientist!


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