In a 12-page study published Thursday in the peer-reviewed journal Science Advances, researchers led by King’s College London and Erasmus University Medical Center Rotterdam examined the genetic analysis of almost 195,000 people from 10 populations across both Europe and Asia.
“We knew of all these people whether they had brown, blue or any other color eyes. Computers searched their DNA for areas that have something to do with eye color. In this way, we found 61 genes associated with eye color, 50 of which were still unknown,” Dr. Manfred Kayser of the Erasmus University Medical Center Rotterdam, said in an article on the university’s website.
“Many genes had to do with pigmentation, but we also found genes that say something about the structure and formation of the iris,” the study’s senior co-author added.
A genetic association study tests whether a given sequence — like a gene — has involvement in controlling the phenotype of a specific trait, metabolic pathway, or disease by comparing genetic material, according to Nature.
“We find evidence for genes involved in melanin pigmentation, but we also find associations with genes involved in iris morphology and structure,” the abstract said. “Further analyses in 1,636 Asian participants from two populations suggest that iris pigmentation variation in Asians is genetically similar to Europeans, albeit with smaller effect sizes.”
In layman’s terms, the researchers found that eye color in people who are Asian with different shades of brown is genetically similar to the eye color in Europeans ranging from dark brown to light blue.
The group said their findings collectively explain 53.2% of eye color variation using “common single-nucleotide polymorphisms” or SNPs.
SNPs are a variation at a single position in a DNA sequence among individuals.
“Overall, our study outcomes demonstrate that the genetic complexity of human eye color considerably exceeds previous knowledge and expectations, highlighting eye color as a genetically highly complex human trait,” the abstract concludes.
In an accompanying release, King’s College London said the results would help to improve ophthalmologists’ understanding of eye diseases like pigmentary glaucoma and ocular albinism.
They also noted that the study — the largest genetic study of its kind to date — was built on previous research in which scientists had identified a dozen genes linked to eye color and that it had initially been believed that variation in eye color was controlled by only a couple genes with brown eyes dominant over blue eyes.
“The findings are exciting because they bring us to a step closer to understanding the genes that cause one of the most striking features of the human faces, which has mystified generations throughout our history,” Kings College London’s Dr. Pirro Hysi, also a co-senior author, said in the release. “This will improve our understanding of many diseases that we know are associated with specific pigmentation levels.”
“This study delivers the genetic knowledge needed to improve eye color prediction from DNA as already applied in anthropological and forensic studies, but with limited accuracy for the non-brown and non-blue eye colors,” Kayser told Kings College London.