How reliable is forensic DNA testing?

Question

I was asking because doing research I think they don't test large fractions of it, they only look at like 13 single variations (or 26?). This shouldn't be as good as TV makes it ou to be, and I hope the public realizes that.

Answer 1

It depends upon the quality of work done by the technicians in the lab!  With adequate quality control and rigorous following the protocols, the results should be highly reliable.

Answer 2

Tv is TV... Facts are Facts!! DNA testing is 99.9% accurate. That should be good enough for anybody!

Answer 3

You are right that forensic DNA testing only examines a small portion of the entire genetic makeup of an individual.  But this small amount of DNA examined has such great variability between individuals that the chance of two unrelated individuals having the same DNA profile at these 13 genetic loci is usually about 1 in a quadrillion (keep in mind there are only about 6 billion people on earth).

Think of it this way:  eyewitness identification may rely on height, weight, s*x, age, hair color, hair length, race.  This is only 7 "variations" (your word choice).  BUT within those 7 areas there can be an almost infinite number of combinations.

Also... looking at the ENTIRE genome of forensic evidence would not be significantly more informative.  A significant amount of DNA is exactly the same between every single human (these are the areas of DNA that make us human).  No information would be gained by determining the DNA profile of the evidence to determine if the donor of that evidence has lungs (the production of lungs is driven by the DNA).

So, your thought that testing the entire DNA of the evidence would be more reliable than only the 13 locations currently tested is correct.  However, the significance of that difference is practically non-existent.

As far as the technology not being reliable:  YES, it is very reliable.  Testing the same individual numerous times produces the same DNA profile.  Comparing the DNA in someone's blood vs saliva vs s***n produces the same DNA profile.  

The same technology used for forensic DNA testing is also being used in the medical field, research fields, and identification of war remains / mass disaster remains.

Caution should be taken when trying to interpret DNA profiles from very degraded samples since no all of the information may be detected.  This is where the experience of the analyst is important in knowing when they should state that the evidence is too poor to draw any reliable conclusions.

Yes, I'm sure in the statistics.

The latest case that I did provided the statistics that approximately 1 in 170 QUINTILLION Caucasians unrelated to the suspect would be expected to have the same 15 locus DNA profile as he does.