21 September 2010

Reconstructing human appearance from DNA

By
Cosmos Online
Police sketch artists might soon be trading in the pencil and paper for a genetics lab. Forensic biologists say they may soon be able to reconstruct a criminal's profile from the DNA they leave at a crime scene.
Police Sketch

Forensic biologists think that one day they may be able to construct the physical characteristics of a criminal from DNA left behind at the scene. Credit: iStockphoto

SYDNEY: Police sketch artists might soon be trading in the pencil and paper for a genetics lab. Forensic biologists say they may soon be able to reconstruct a criminal’s profile from the DNA they leave at a crime scene.

This would potentially render DNA databases obsolete, said molecular biologist Manfred Kayser from Erasmus MC in Rotterdam in his keynote address at the 20th International Symposium of Forensic Science, in Sydney in September.

This kind of approach could revolutionise police work. Particularly in relation to so called ‘cold-cases’, where the DNA sample does not match a suspect’s profile or that of any criminal in a DNA database, Kayser said.

Gender and pigmentation

“We don’t yet know if it’s possible to find accurate genetic markers for individual specific traits [such as facial dimensions] … if we do, it could eventually mean that criminal databases won’t be needed. For now that’s of course science fiction,” Kayser told the Sydney audience.

Most physical characteristics are complex traits, defined by several interacting genes and possibly environmental factors too. Yet, Kayser and others in the have already identified several DNA markers that determine various physical characteristics, including gender, hair colour, eye colour have already been discovered

The simplest characteristic to determine with a DNA sample of unknown human origin is gender. The gene for amelogenin (a protein involved in tooth development) can be used in sex determination of samples, because the length of the gene is different on the X chromosome to the Y chromosome. This is a relatively robust, but not foolproof, gender test, according to Kayser.

Hair colour prediction underway

Beyond gender, the human traits with highest predictive accuracy are those affected by pigmentation, simply because they are the least complex. Red hair colour, which is determined by a single gene, can be predicted with a certainty of around 93%.

For other hair types, accuracy is slightly lower, but still promising. Kayser reported confidence levels as high as 85, 81 and 80% for predicting black, brown and blond hair respectively.

Perhaps the most progress has been made in determining eye colour: Kayser and colleagues reported that using DNA they could predict with 90% confidence if a person of European origin had blue or brown eyes, based on an analysis of just six positions on the genome.

Eye colour, height and even age next

Although the predictive accuracy is less robust for intermediate eye colours, new genes, involved in the subtle variation of iris colour, are being discovered all the time, Kayser said.

Some traits, however, are inherently problematic. While height is a classic example of an inherited trait, it is notoriously difficult to predict. This is because there are more than 50 DNA markers associated with height.

Kayser also alluded to alluded to research, in press, detailing tools for predicting human age. Thus far, the most promising technique for separating the young from the old involves the analysis of ribonucleic acid (RNA) – a molecule chemically similar to DNA but principally involved in protein synthesis and gene expression.

There is also emerging data for a raft of other traits, such as skin colour, freckles, baldness and hair morphology, Kayser said.

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