DNA question

I'm no forensics expert, but I have a friend who is a tech in a DNA research lab.

1. Without attached skin or the follicle, a hair is useless for DNA testing. That said, if there are already hairs in evidence, there's other things that can be done for a match besides DNA (comparison microscope comes to mind easily).

2. Depending on what kind of sequencing they're doing, the test itself takes from 12 to 36 hours to run (IIRC). HOWEVER, 99.9% of the labs are extremely backed up in the workload, which is why it can take days, weeks, months to get results back. From what I understand, if your right people know their right people, you can get a quicker turnaround time, but standardly it takes a couple-three weeks at best to get results back from what I've heard.

So, basically, you can make it work for your story however you want it to happen--but don't take your guidance from CSI. Their labs are someone's wetdream from all I've heard from my friends in the field.

A DNA test can be performed in as little as 3-5 days.
Here again it's the substance/object which is being tested that can cause the delay.
In DNA comparison tests (for example: paternity), you have 2 persons with DNA being tested. Relatively easy being you either have a match of a DNA strand or not.

When testing hair, skin, and body fluids with no comparison it may take a considerable amount of time to find a "match". In some cases weeks and others up to 3 months.

Edit:
There can be dried skin/dander in human hair that can be tested.
Doesn't have to be a follicle. Poor woman could have a bit of dandruff and that can be tested.

mollyluna said:

He's a billionnaire; she's a poor librarian. He can afford to have it rushed. This is very very helpful. Could you elaborate on the microscopic hair test? How long would it take and how accurate would it be? Is there any likelihood that possibly one hair follicle/skin tag might be in that hair just because we shed so much on a daily basis?

thanks.

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Comparison microscope: http://en.wikipedia.org/wiki/Comparison_Microscope

This article only talks about the ballistics applications, but I've seen on shows where they use it for hairs and fiber samples as well.

Losing one's follicle is fairly rare because that's in the skin and what grows the hair from what I've heard. Having a hair plucked out on purpose is usually the best way of harvesting for a DNA sample (think of plucking eyebrows)--though some could be pulled out in a fight I'd guess.

mollyluna said:

hair is proof of life.

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Hair with or without follicles would never be considered proof of life. It might depending upon circumstances be proof of who was kidnapped, but not that they were still alive.

Hair alone can be tested for drugs and poisons which remain in the hair. Blood taken out would need to be stored with an anticoagulant or it will clot very quickly then breakdown. If you've ever donated blood, the receiving bag has fluid in it that is an anticoagulant. The blood then would need to be stored in a fridge so the blood wouldn't die. Shelf life is short, 6 weeks for whle blood but cryogenesis can hold red blood cells (in gycerol to prevent freezing and bursting) up to 10 years.

No on the blood for proof of life, Molly.
Are you stuck on a biologic example or can your story go with a more conventional p-o-l such as talk to her or hero gets to ask kidnapper a spontaneous question (what was her childhood best friend's dog's name?) to demo p-o-l.

mollyluna said:

How about a vile of blood that hadn't separated/coagulated yet? It separates into red cells and serum in what, two hours? Or is it longer?

thank you!

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No it would separate only if in a tube containing anticoagulants and then it's usually minutes not hours. The labs use centrifuges to separate the clot from the serum. Without the anticoagulant the blood will clot in a matter of minutes

>she's kept drugged and unconscious for the whole five days.

Small problem here, completely out for 5 days, a person will still excrete and urinate for 2-3 days--and someone will need to clean them up, then the victim will become dehydrated and weak from lack of food, causing secondary problems.

Every 24 hours of not moving loses at least 96 hours of muscle tonus. Your victim would be unable to walk after 5 days of complete unconsciousness, no food, no water.

Without water that long they'd have kidney dysfunction, severe low blood pressure, massive headaches, be into shock, and have numerous other health issues.

mollyluna said:

She's hooked up to an IV drip and cleaned up. No problems there. Isn't an IV sufficient for water/food for 5 days?

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Yes, but only barely, assuming the IV fluid has the correct salt concentrations and some sugar (typically 5% dextrose). Generally for folks in comas if we can't give liquid feedings down a tube through the nose we at least give some high-potency (and specially formulated) IV fluid. Five days on a simple IV is plausible, though, if the person was otherwise healthy before that.

She'd still be weak and very wobbly.

Back to the blood thingy, red blood cells have no nucleus, ergo no dna/rna to match, (they carry oxygen in that space)you can only do blood type match, A, B, AB, & O: each positive or negative. White blood cells do have nucleui and can be used for matching.

Actually, DNA can be matched from a blood sample. The problem in this scenario, is that a DNA match does not prove the the person from whom the sample was drawn is *alive*.
Molly, a non-verbal p-o-l may be possible, but it hasn't sprung to my mind. Can't your bad guy hire a lackey to do the face to face, put her on the cell phone, convey the question about what color the boat house was at her summer camp, etc?
And then when you need another dead body..."Sorry, Lackey. Looks like you're wearing the wrong color shirt on this episode of StarTrek."

I just want to back up to the discussion on time frame to have DNA testing done. I work in a DNA lab (no, I can't answer actual DNA questions because that's not my particular area of expertise) and can comment on how backed up they get. The state lab in Louisiana is backed up almost 2 YEARS. The lab I work for just opened this past summer, and is already backed up over two months, and that's only serving one parish.

However, there are private DNA labs that the billionare could use, so that problem would be moot for this particular scenario. But, I just want to give you a ginormous cyber-smack for thinking that ANYTHING on CSI can be used as reference material. That show is the biggest pile of utter fiction I've ever seen. Please, please, please do NOT think of that show as an accurate depiction of what real-world crime scene processing is like. I worked in crime scenes for many years, and there isn't a single person who works crime scenes or in crime labs in the real world who does not mock that horrid show mercilessly. Their budget would have to be in the BILLIONS to be able to run all of the tests that they do, plus juries now have a very skewed concept of what is possible with forensic testing, which is making it very hard to get convictions. http://crimelabproject.com/


Watch it for the enjoyment of the plot and the story as you would any other science fiction show, but please don't think that it's realistic in any way.

And I apologize for the slight threadjack and the soapbox moment, but I can't stand the thought of seeing these myths about forensic testing perpetuated in even more fiction.