Eye colour is still used to teach genetics in school, with students learning brown eyes are dominant over recessive blue eyes.
This is a hangover from the days when it was believed that eye colour was determined by a single gene, with one copy inherited from each parent and the eye colour of the child determined by the most dominant version.
It caused some confusion when blue-eyed parents had a brown-eyed child!
A continuum of colour
Now we know that eye colour is a complex genetic trait, controlled by multiple genes that produce a continuum of eye colours that move through a spectrum of brown, amber, hazel, green, blue and grey. But the myth of a single gene for eye colour is still perpetuated, probably because it is a simplistic teaching tool.
One of the main genes that influences our eye colour is OCA2. Eye colour is related to the amount of melanin – molecules that produce pigment, among other functions – in the front layers of your iris. Brown eyes have a large amount of melanin and light blue eyes have much less.
OCA2 is involved in the production, transport and storage of melanin. Oculocutaneous albinism, which results in very light skin and light-coloured irises, is caused by a mutation in OCA2. A specific mutation in a sequence within the adjacent HERC2 gene regulates the function of OCA2 and plays a role in blue/brown eye colour. Other genes with lesser effects are also involved in skin and hair colouring.
Over 60 genes taking part
In 2021, IMB’s Professor David Evans collaborated in the largest genetic study of eye colour to date, to find out if there were more than 11 genes involved in eye colour.
“We were surprised to find a further 50 genomic regions associated with eye colour – many of these genes were linked with melanin pigmentation, but we also found others associated with the structure and formation of the iris,” Professor Evans said.
“This study clearly demonstrates that the genetic complexity of human eye colour considerably exceeds previous knowledge and expectations.”
So if you learnt the ‘one gene, one colour’ basic genetics, it’s back to school!
