Elsevier journal publishes groundbreaking research on genetic inheritance

Article in Trends in Genetics explores relation between eye colour, pigmentation genes and ancestry.

London, 22 June 2004– Skin, hair and eye colour have fascinated those studying inheritance in families since the dawn of genetics. Dr. Richard Sturm and Dr.Tony Frudakis, writing in the August issue of Trends in Genetics, argue that one of the classic examples of genetic inheritance taught in schools is wrong. Their research shows that the colour of our eyes is influenced by the interaction of several genes. Using special markers (called ancestry informative markers, or AIMs) that can identify the genetic differences between different populations, they have identified the sequences that explain variable eye colour in Europeans. AIMs have important applications in forensic science and can be used to shed light on human ancestry.

The concept that is commonly taught in schools is that brown eye colour is always dominant to blue, that two blue-eyed parents always produce a blue-eyed child. This is simplistic and does not convey the complexities of real life. Although it is not very common, two blue-eyed parents can produce children with brown eyes. “There are examples of blue-eyed parents having darker eye coloured children. This is because eye colour is determined by several interacting genes,” said Dr. Richard Sturm, Principal Research Fellow, from the University of Queensland, Australia.

Although the OAC2 gene on chromosome 15 is the major determinant of brown and blue eye colour, analysis suggests that other genes are also important in determining eye colour. “There is a predominant gene for blue/brown eye colour but it is not an absolute determinant. There are subtleties of eye colour and a range of hues that we cannot yet fully explain. Many other genes do influence the type of eye colour we see in the European population,” said Sturm.

The physical basis of eye colour is determined by the distribution and content of melanocyte cells (the specialised cells that produce melanin) in the eye. Brown eyes have an abundance of melanocytes, whereas blue eyes contain only a little melanin. Differences in melanin pigment produce the range of eye shades observed in humans. “In the eyes, the melanin is packaged differently and retained in the cells that produce them. Because of this, eye colour has a structural basis,” said Sturm.

“Blue eye colour is actually due to a light scattering effect (similar to the blue of the sky) of the packaged melanin – not due to the colour of the pigment itself,” said Sturm.

He added, “As more melanin is packaged, the darker the eyes become and the brown colour is more the colour of the pigment. If we can understand what regulates the packaging of the melanin in the eye, we will have a much better understanding of the basis of a persons eye colour.”

Indeed the colours of our eyes, hair and skin are linked. The same genes affect the production of melanin in all of these tissues. However, certain genes will have more influence on one tissue than another.

“The genetics of eye colour must be seen as for skin colour. Darker traits [tend to] go together but we do see individuals with blue eyes and black hair. Eye colour may be a touch more sensitive to the genes affecting melanin pigment synthesis because the eyes do not make melanin continuously as is the case with the hair and skin,” said Sturm. “There are as many hues of eye colour as there are of skin colour. Because we often simply [see] these traits as a dark or light dichotomy, the subtlety and realisation that it is a continuum of shades along a spectrum is lost. We have a major blue/brown distinction in Europeans, but we also have grey/green/hazel and every shade in between.”

AIMs will have many applications in forensic science. “We are using all of these sequences to develop a model to classify gross iris color shade from an unknown DNA sample (such as might be found at a crime scene) and this product is in the final stages of commercial development, “ said Dr. Frudakis, director, DNAPrint Genomics, Inc, based in Sarasota, Florida. “We hope to do the same for hair color and skin shade and have made preliminary progress on both of these traits. Hopefully in the near future, these products, combined with products for the inference of ancestry and ethnicity, will enable a physical profile of a suspect to be reconstructed from DNA found at the crime scene.”

About Trends in Genetics

Trends in Geneticsis a forum for all aspects of current research in genetics, developmental biology and genomics. Every issue of Trends in Genetics contains concise, informed and timely reviews that synthesise for a non-specialist readership current topics in these fields.

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