Forensic DNA testing

Field advancements in DNA testing have been making their presence felt for the past 10 years, and there’s a lot of controversy surrounding forensic DNA testing, mostly due to some controversial results. But science is always improving, and this type of analysis is definitely much needed in forensic studies.

How forensic DNA testing works

Virtually any advanced organism carries around DNA after which it can be identified; we’re not yet at the level where we have decoded the DNA code of every animal, but we’re pretty good at studying humans.

DNA profiling is a technique used by forensic scientists to assist individuals by their DNA profiles. Basically, DNA profiles are encrypted sets of information that reflect a person’s DNA genetic make-up. However, DNA profiling shouldn’t be confused with full genome sequencing – which is an entirely different thing.

Basically, over 99.9% of everybody’s DNA is identic; but the 0.01% is enough to differentiate between all of us. To identify individuals, forensics typically scan 13 DNA regions, or loci, that vary from person to person and use the data to create a DNA profile of that individual – basically you can consider this as a DNA fingerprint.

The DNA code, as long and twisted as it may be, basically consists of four nucleotides:
- Adenine
- Cytosine
- Guanine
- Thymine

Any DNA molecule consists of these for elements, linking together like rungs on a ladder, 2 by 2 (Adenine and Thymine always go together, and so do Cytosine and Guanine). It’s these combinations that basically make everybody unique.

DNA samples

You can take DNA samples off of virtually everything: clothes, hats, weapons, condoms, cigarette buds, bottles, cigars, stamps, books, linen, fingernails, and even directly from other people. When you see forensic technicians taking samples, they place them in paper bags or paper envelopes – not plastic bags; this is important because plastic bags retain moisture, which can significantly damage the DNA samples. After this, the samples are taken to the lab, where they are subjected to thorough analysis.

Nowadays, many labs have the ability to conduct DNA testing, though the capabilities greatly vary; only a few labs offer more specialized techniques, such as Y-chromosome or mitochondrial DNA analysis, on which I’ll go into more detail in future posts.

How effective is DNA analysis?

Let’s consider this situation. Say that type O blood is found at a crime scene; this blood type occurs in almost half of all people, so this doesn’t really say much. But say they also find markers which suggest he is blond. That starts limiting it a little, but it’s still not definitive – and this is where things start to get tricky, and it’s easy to make mistakes, because the reference sample is sometimes damaged and coincidences can occur, and sometimes do, though less in recent times. In the early days of DNA foernsic analysis, juries were often swayed by statistic considerations presented somewhat one-sided or downright misrepresented:

“[your honor,] given a match that had a 1 in 5 million probability of occurring by chance, the lawyer would argue that this meant that in a country of say 60 million people there were 12 people who would also match the profile”

The argument is not valid unless the suspect was drawn at random from the population of the country – so alone, DNA evidence is not entirely relevant. But coupled with other evidence, that’s an entirely different story. The odds of a suspect DNA matching the DNA analysis found at the scene is all but impossible by coincidence.

However, DNA evidence can be faked, it can be planted upon and it can be tampered with. In the case of the Phantom of Heilbronn, police detectives found DNA traces from the same woman on various crime scenes in Austria, Germany and France — among them murders, burglaries and robberies. Only after the DNA of the “woman” matched the DNA sampled from the burned body of a male asylum seeker in France, detectives began to have serious doubts about the DNA evidence.

I don’t wanna go into more details about forensic DNA testing, hopefully you have an idea by now on what it means, how it works, what are the upsides and downsides. I’ll try to get more into the details of this technique and as I do this, I’ll start adding links to this post, so hopefully you’ll have all the info centralized.