Brown or blue eyes are most desirable
Eye color genetically more complex than expected
For a long time, eye color was considered a trait controlled by only a few genes. In a study among almost 195,000 people in Europe and Asia, researchers have now discovered 50 new gene variants for the color of the iris. The genetics of human eye color are therefore much more complex.
An international research team led by King’s College London and Erasmus University Medical Center Rotterdam has identified 50 new genes for eye color in the largest genetic study of its kind to date. The study, published in Science Advances in mid-March, included genetic analysis of nearly 195,000 people in Europe and Asia.
Blue eyes “only” for 10,000 years
Around 90 percent of all people worldwide have brown eyes, including the vast majority of people of non-European descent. The rest is divided into blue, green and gray, with green being the rarest eye color with less than 2%. There are very few brown-eyed people in the Baltic Sea region: in Estonia, 99% of the population have blue eyes (source: Wikipedia).
People of European descent show the greatest diversity in eye color. The differences are due to different proportions of the pigments melanin and pheomelanin in the iris. If the black-brown melanin predominates, the eyes appear brown, with a larger proportion of the lighter pheomelanin the eyes are green or gray. If the pigments are completely absent, blue eyes appear. According to genetic researchers, the blue variant “only” appeared 6,000 to 10,000 years ago.
Gray and green eye color puzzles
In the beginning, scientists thought that the variation in eye color was controlled by just one or two genes. In further research, researchers identified a dozen genes that are related to eye color and that allow, for example, to predict whether a person has blue or brown eyes. However, gray or green eyes were left out. Even then, the scientists assumed that there would have to be more genes for this.
Largest comparative study in Europe and Asia
In search of these additional genes, the researchers from London and Rotterdam carried out the largest genome-wide comparative study to date. To do this, they analyzed the genome of almost 195,000 people from ten populations in Europe and two in Asia.
In doing so, they specifically searched for gene locations and point mutations that occur more frequently in people of the same eye color - and discovered 50 other gene locations in which gene variants for the eye color are located and which explain some of the genetic connections that were previously missing. Amazingly, many of these gene variants were also found in Asians, although their eye color "only" varies between different shades of brown.
Help for medicine and forensics
According to the researchers, these findings will help improve our understanding of eye diseases such as pigmentary glaucoma and ocular albinism, in which eye pigmentation plays a role. In addition, the newly discovered gene variants can now help forensic scientists and anthropologists to determine the eye color of skeletons more precisely using DNA during archaeological excavations or criminal investigations.
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