Today we’re going to talk on DNA and forensics. This is a subject that embraces several disciplines; there is by one in genetics to explore the various regions in the genome;
then, statistical genetics, that calculates probabilities of given hypothesis; and then law: the evidences obtained by the DNA that is presented to court. So, we’re going to explore the three of them but focusing mostly on the third one because is more far away from genetics and DNA itself. Alex is an officer at National Institute of Toxicology and Forensics of the Ministry of Justice in Barcelona. Alex did his PhD on genetics in cancer studying microsatellites in oncogenes and tumour suppressor genes
and then became involved in forensics and the analysis of evidences from de the field of police and judicial investigator: homicides, sexual assaults, identifications, paternities and so on. He also issues the expert reports in trials so he’s going to talk on this very, very special application, a direct application of genetics in court. Alex, thank you very much for being here. Which kind of cases do you deal with in forensics? Which are the problems that you try to solve? Yeah, well, most of the cases that we deal with in our laboratory are sexual assaults, but we also deal with homicides, with identification of human remains and also paternity and kinship testing.
From all of them, we analyse samples that we receive both from forensic doctors or from the police departments and, well, our aim is to try to find out or to identify the person who for instance has left biology fluids in the scene of crime or in a victim and so on. The problems in forensics, forensic genetics, I would say, mostly are due to the low quality of the DNA that we can obtain from the evidences. This is because the grade of degradation or the low amount of DNA present in the evidences difficult very much our analyses and, at the end, the outcome of our results. This would be, perhaps, the most important problem that we have to deal with.
Which kind of genetic analyses do you perform on the samples you are analysing? Yeah, once we receive the samples in the lab, first of all, we have to make an identification of the biological fluid that we are looking for. This means for instance semen, saliva, blood, remains, among others. And from here we have to try to make a DNA extraction by using different techniques from both organic extraction methods to maybe automatic extraction methods too. And after that, from most of the samples we have to perform quantification of DNA analyses usually using real time PCR techniques.
And after that the kind of genetic marker that we study, the most are Short Tandem Repeats or STRs because they are very spread, used around the world, because they are highly polymorphic among the populations, they’re quite easy to analyse and also because they are the kind of genetic markers used in genetic DNA data bases both from criminal or humanitarian purposes.
After that, using also PCR techniques and afterwards mostly capillary electrophoresis procedures, we obtain our genetic profile, and this is our main tool to deal as the same way, perhaps, a medical doctor with the results and analyses from blood samples or any, any other kind, and he makes his reports, so this is our tool, our main tool, is the genetic profile that we obtain from the samples, both from unknown samples and also from known samples from suspects, victims and so on.