Forensic scientists could use DNA retrieved from a crime scene to predict the surname of the suspect, according to a new British study.
It is not perfect, but could be an important investigative tool when combined with other intelligence.
The method exploits genetic likenesses between men who share the same surname, and may help prioritise inquiries.
Details of the research from the University of Leicester, UK, appear in the latest edition of Current Biology.
The technique is based on work comparing the Y chromosomes of men with the same surname. The Y chromosome is a package of genetic material found only in males.
It is passed down from father to son, just like a surname.
“The evidence would not be hanging on the Y chromosome, all it would give you is an investigative tool to prioritise a sub-set of your suspects,” said co-author Dr Mark Jobling from the University of Leicester.
Mining the information would require building a database of at least 40,000 surnames and the Y chromosome profiles associated with them.
Dr Jobling emphasises the limitations of the method; it could have some predictive power in just under half the population, after the most common surnames like Smith, Taylor and Williams have been excluded.
But he says it has the potential to cut down on the police workload.
“If you had a big enough database, it would give you from your crime scene sample a list of names,” Dr Jobling, from the University of Leicester, told the BBC News website.
“That would help you prioritise your suspect list. Some investigations have very large suspect lists, in the thousands.”
The Leicester researcher said police could consult the Y chromosome and surname database to help prioritise their search in cases where a crime scene sample had failed to turn up matches in the national DNA database.
“You might have a situation where the Y chromosome predicts 25 names. So you could go and see in the pool of suspects whether the names are there,” Dr Jobling explained.
“If they are¿ you could then ask them for a DNA sample and do conventional DNA profiling to see if they match the crime scene sample.”
Over time, the Y chromosome accumulates small changes in its DNA sequence, allowing scientists to study the relationships between different male lineages.
It follows that men with the same surname might have very similar Y chromosomes. But adoptions, infidelity, name changes and multiple founders for just one surname complicate the picture.
For the study, Turi King and colleagues from the University of Leicester recruited at random 150 pairs of men who shared a British surname and compared their Y chromosomes.
Across the sample, the authors determined that just under a quarter of the pairs had recent common ancestry.
Given the small sample size and the random recruitment, Dr Jobling said he was surprised at the strength of the signal.
Sharing a surname also significantly raised the likelihood of sharing the same type of Y chromosome, with the link getting stronger as the surname gets rarer.
The researchers used the data to roughly test the predictive power of the method. They found the approach was most useful for less common names, with a 34% chance of prediction in the 80 least common surnames from the 150-name sample.
“This range of surnames makes up 42% of the population. So we’re looking at prediction in just under half of the population. We have to exclude the Smiths and Joneses,” Dr Jobling said.
The researchers extrapolated their success rate to the 25-65 no-suspect murders and 300-400 no-suspect rapes on the police books each year, and found the method could help in roughly 10 murders and 60 rapes annually.
Max Houck, a former scientist with the FBI Laboratory, and director of the Forensic Science Initiative at West Virginia University, US, commented: “I think by itself it is probably not useful—a single point of evidence—and for most evidence types that’s the case.
“But if you have that and other data, it can put you more towards or more away from a particular proposition if you know the person may have an uncommon surname, and, for example, some ethnicity information.
“If it’s a bit more cumulative it might push you in a particular direction,” he told the BBC News website.
It was at the University of Leicester in 1984 that the technique of “DNA fingerprinting” was first developed.