A new DNA test will help police in the UK solve rape cases even when the attacker has not left any traces of sperm,reports the New Scientist reports.
According to researchers from Birmingham's Forensic Science Service the test traces the genetic hallmark of other cells present in semen, such as skin and immune cells, and is likely provide DNA evidence in a further 90 sexual assault cases a year, Charges have already been brought in a case reported earlier this year..
A common problem for forensic scientists hoping to use DNA fingerprinting to identify assailants in sexual assault cases is that the quantity of male DNA in swabs taken from the woman is often tiny compared with the amount of hers present.
Conventional methods of amplifying small amounts of DNA do not work because the female DNA would be amplified as well.
The team headed up by Andy Hopwood from the Forensic Science Service looked at ways to isolate the male component using enzymes that destroy the coating of ordinary cells, leaving intact only sperm cells.
But this is not possible in every case - in 10-15% of the cases the FSS deals with, no sperm can be found in the semen, either because of a medical condition or because the male has had a vasectomy.
In tests the FSS scientists combined a method called laser microdissection, which enables any male cells carrying the Y chromosome to be extracted from a microscope slide, with fluorescence in-situ hybridisation, which can highlight unique DNA sequences within cells.
With these, and the FSS's super-sensitive DNA Low Copy Number analysis, the scientists were able to obtain accurate male genetic fingerprints from vaginal swabs taken up to 24 hours after sexual intercourse, even when no sperm were present.
Research manager Martin Bill said to the New Scientist that it will help them to obtain vital DNA profiles in a further 90 sexual assault cases a year that have previously been just too difficult to get a usable DNA profile from.