More and more details are being gathered about how exactly human genes influence medically relevant traits, such as the propensity to develop a particular disease. The ultimate goal would be to predict whether or not a given trait will develop later in the genome sequence alone (i.e. from the sequence from the bases that comprise the DNA strands that store genetic information in each and every cell from the body).
Now, writing in the journal Current Biology, a Cell Press publication, several researchers make up the Netherlands put this goal to a test using eye color. The group around Manfred Kayser from the Erasmus University Medical Center Rotterdam showed that it can be predicted with an accuracy well over 90% whether an individual has blue or brown eyes by analyzing DNA from only 6 different positions of the genome.
Human the color of eyes, which is based on the extent and type of pigmentation on the eye’s iris, is exactly what geneticists call a ‘complex trait’. Which means that several genes control which color your eyes may ultimately have. Over the past decades numerous such ‘eye-color genes’ have been identified, and people with different eye color, have a different DNA sequence at certain points during these genes.
Such differences are known as single nucleotide polymorphisms (SNPs). Manfred Kayser and the colleagues analyzed the DNA of over 6000 Dutch people whose the color of eyes have been scored. They determined the sequence at 37 SNPs in 8 the color of eyes genes for every of these and located that the the color of eyes of the given individual can be predicted with more than 90% confidence already with the best 6 SNPs from 6 genes, as long as the person’s eyes are blue or brown. For the intermediate color, shown by about 10% of those tested, the precision is lower at about 75%.
The implications of the study are two-fold. For one, it is a proof-of-principle that complex traits could be predicted from the genome sequence alone, so long as genes with strong effects around the trait exist and therefore are known. This could have implications for predicting disease risks based on DNA, prior to the disease breaks out. Additionally, these bits of information have direct relevance in the forensic sector. Think about a case in which the only trace from the suspect is really a DNA trace but the DNA profile generated doesn’t match that of known suspects or any in the Criminal Database.
There currently is in fact one such open case in Germany where the DNA of a single woman was found at a large number of crime sites over many years. While using approach of the new study, the eye color of a suspect”” as well as in principle also other traits for example hair color “” could be predicted, thus assisting to find unknown suspects. Needless to say, there are also caveats, one of them would be that the prediction was only tested for individuals of Dutch European descent, and, although expected, it needs to be shown that similarly high prediction accuracies are obtainable in other populations across Europe.
Also, the toughness for such DNA-based eye color prediction test currently depends on a precise knowledge the unknown person whose DNA was tested is of European descent, because the used SNPs are associated with eye color but have no direct functional implications as far as known. Inferring highly accurate info on European ancestry from a DNA sample isn’t trivial, although such scientific studies are underway as well.
The researchers include Fan Liu, Kate van Duijn, Johannes R. Vingerling, Albert Hofman, Andr© G. Uitterlinden, A. Cecile, J.W. Janssens, and Manfred Kayser, of Erasmus University Medical Center Rotterdam, Rotterdam, The Netherlands.