Doctor shines light on DNA in Forensics

Any contact between human beings leaves behind DNA (Deoxyribonucleic acid.) “When we shake hands we exchange sweat and this as well as saliva, hair and anything containing nucleated cells hold DNA,” explained Dr Valery Alexandrov, a forensic pathologist for the past 40 years who is currently based at the Forensic Science Centre in St James. Dr Alexandrov, who has studied and worked with DNA exclusively, spends most of his working hours uncovering evidence to help police solve murders—the type found on a victim’s body and left, usually unknowingly, by attackers. DNA is found in any nucleus containing cell in the body—every cell except for red blood cells and the skin keratin. The millions of DNA in the human body are contained in sweat, saliva and even hair. Every human being gets 50 per cent of their DNA from their mother and 50 per cent from their father. “This is the basis for paternity testing,” said Alexandrov. 

 

 

In clinical applications, DNA can indicate genetic abnormalities, mutations and radiation that causes genetic mutations.“If you have  even a single cell, you can extract DNA,” he said, adding that the science DNA is an analysis of match. Alexandrov said before DNA evidence was introduced to courts, police relied on blood groups to investigate crimes. “The problem was that most of the population have the same blood groups so the evidence was sometimes inconclusive,” he said. “DNA evidence is 99.99 per cent accurate and has made a remarkable difference in forensics.” However, Dr Alexandrov said, DNA can be difficult to understand. “People are usually misled, I think by the media, they think autopsy is a magic tool that solves crimes. “The autopsy, which includes DNA evidence, is important and essential but only when combined with a police investigation. An autopsy cannot solve crimes.”  Alexandrov said people usually believe if DNA is found on a body at a crime scene, it is 100 per cent implied that the victim was assaulted.

 

 

“It’s not like that. I can compare it to finding semen on a body. This is indicative of intercourse but not rape. Finding foreign DNA on a body just means the person had contact with someone else,” he said. “The rest of the scenario, whether a beating or a touch is a matter of police investigation.” How it’s done? “In our autopsy, we take finger nail clippings and when possible blood from the victim. He said a pathologist can determine that DNA was transferred, but not why. “The blood DNA and finger nail DNA will match 100 per cent but the presence of foreign DNA indicates physical contact which shows DNA transfer,” he said. A technique known as Polymerase Chain Reaction (PCR), where special enzymes are applied to DNA to cut out pieces of it, separates identical pieces of DNA leaving behind pieces that do not match. Alexandrov said problems can occur in the process but are based on human rather than method failure.

“The major problem with DNA is contamination from using instruments that aren’t sterile, from mould and air particles—almost anything can contaminate DNA.” 

 

 

He said this is a big problem because when DNA specialists go to court they will always have to answer whether the sample was contaminated. He said at the crime scene, the pathologist takes DNA samples and gives it to a police officer who takes it to an evidence room. The person in the evidence room will take it to the lab where it is distributed among lab personnel. “Every sample passes five to six hands so there is a lot of room for contamination,” said Alexandrov. In the United States DNA evidence is produced in court quite frequently but it rarely reaches the courts in T&T.  He said DNA evidence is used locally but because of the structure of our legal system, it takes longer. “There are five forensic pathologists that I know that are from this country and they all work in the United States,” said Alexandrov. He felt that this was unfortunate but added that forensic pathologists were always in demand and the US offered more in terms of compensation.