DNA testing speed

[gibbie99]

THis has nothing to do with OBL. But alot of people are asking about how fast it takes to test DNA. Mostly we use PCR method, it's gotten much faster; it used to take 4 hours. Now with fast cycling you can get results in an hour. But still there is the DNA processing, that takes 2 hours easily. Also you have to run the microsatellites on a gel, that could be an hour for agarose or all day for poly acrylamide. I have no idea what they did to confirm/validate the results, but 24 hours is not unreasonable length of time. Any lower, i'd be suspicious. It really depends on what tests they did. Some take days, some not.

If anyone cares about bona fides, i have done forensic dna analysis, i have 13 years lab experience and several graduate degrees.

[Tziva]

For people who are more interested in this, one of the blogs I regularly read posted something similar today, with lots of details and tasty information:

http://scienceblogs.com/observations..._osama_any.php

(It's very interesting, I recommend reading it if one is at all interested in this topic)

[Addamus]

So you went to school for forensics? Not to be a creep, but I'd kinda like to talk 1-on-1 with you about it. I'm currently at the end of my second year as a forensic biology student and I'm thinking of specializing in serology.

[Catta]

yea but... PCR is needed when u dont have sufficiently DNA for testing... I dont see the difficulty of just cuttin up some DNA from father and son then put it into a gel-electroforesis

[Auralan]

I can hear the sound of crying CSI fans all over the world.

Awesome stuff, this is.

[gibbie99]

yea but... PCR is needed when u dont have sufficiently DNA for testing... I dont see the difficulty of just cuttin up some DNA from father and son then put it into a gel-electroforesis

No offense, but the human genome is 3 billion base pairs, separated into 23 chromosomes, eacch millions of base pairs. A typical agarose gel can only handle 4kb to 400 bp, thereabouts. So you see, if you did a restriction enzyme digest, with a typical 6 bp cutter, that is only 4^6 / millions of bp = many fragments, handle it! Can't be resolved. Some of my work actually went into figuring out ways to handle RE digests of genomes. We used HPLC to separate out DNA with base pair precision. It was still a giant mess. What people do when they analyze genomes is do these RE digests then stick them into artificial chromosomes, YACs or BACs (yeast or bacterial artificial genome). Once you get the genome into million bp fragments you can take each fragment and cut it further, then finally walk your way through small plasmids (10kb typical insert). In this fashion the human and many other genomes were sequenced. (I worked on this project, along with many many others).

Anyway. There are two main ways to do forensic DNA analysis now. Microsatellites, which are highly polymorphic sequences in the genome, created by repeat sequences such as TACTACTAC, or by SNPs, single nucleotide polymorphisms. I do not know much about SNPs, it's a chip technology, I think it takes quite a bit of DNA and quite a long time to analyze. I am a microsatellite expert, my MS was in that technology. Microsatellites can be analyzed in a day. I dont' think anyone does sequencing, way too much DNA required. Also we used to do RFLPs, but again that took alot of DNA (not to mention high technical expertese).

[Silmariella]

This is a very enjoyable thread

your friendly neighbour biochemist