Great, thanks for all the info. One last thing: could you tell approximately how old the blood is, ie how long it’s been since the murder or whatever it was?
Uh, no. Well, only in the vaguest of terms. Wet stain with clots still on it, dry stain with wet clots, red-brown stain, brown stain. Fresh, drying, dry, older. No hard number of days or weeks attached. Once it’s old, it stays old. Analogy: any scar on your skin. Say it took a week to go from fresh cut to healing scar with scabs coming off, and six months to mature to old scar. Once it matured to its final form, it stayed that way for years, and no one can tell whether you got it six months ago or sixteen years ago.
DNA extraction from the buffy coat of a spun-down EDTA tube, using Qiagen QIamp kit. ~25 mins from draw to quantitation at 260 nm. We have not had good luck with buccal scrapings, and that may be due to a lack of cell deposited on the scraper. We did find a good protocol for extracting DNA from a forensic brain specimen, but I forget the steps at the moment.
Vlad/Igor
When I gave birth to my daughter, they gave me a sealed packet of what I assume is blood. It is a metal foil packet placed in a ziploc baggie and written on it is: DNA Card with her sex, name, DOB and a 4 digit number. As well as a happy little note that says: Do Not Open.
It seems nowadays, they give you a sample of your childs DNA from the get-go. I would find it hard to believe that I am raising her and would not have her DNA hanging around the house, but I think it’s a nice policy that makes it “easier to find” I suppose. Speaking of which, can you get DNA from poo? What parts of us do NOT give DNA?
Is a drop or two enough blood, or would a diligent parent gather other little bits (hair, nails) to give other information? Or is DNA pretty much the end all be all?
Sorry, I have a 7 month old, poo is my life. 
No, this isn’t a way to get vlad and gabriela to continue waxing poetic on this interesting subject, why do you ask?
That’s interesting; I hadn’t heard of getting a blood spot on a newborn hermetically sealed like that. No, you don’t want to open it (I know, curiosity is killing you), as you will contaminate the sample with DNA from your sloughed skin cells. I think it might be a bit over the top to give you such a sample, because as you point out, she’s leaving a trail of crumbs as it were by licking, drooling, handling toys, getting her hair brushed or being dried off by a towel. ID by DNA can be done from cells left in the environment, and blood relationship determined by comparing nonsense repeats in the DNA. It sounds like the foil packet is some attempt at a chain-of-custody, where her sealed sample is given to you, so that you can later identify it as coming from her.
Ah, yes, stool samples. Wonderful things those. Never open one unless it’s under a fume hood. While it is theoretically possible to get human DNA from intestinal cells that hitch a ride with the poop, it would be damn near impossible, as intestinal bacteria outnumber the human cells about a gazillion to one (and make up about a third of stool by weight).
Vlad/Igor
Also, stool tends to be very fatty and just generally difficult to work with. It can be done, but as Vlad said, there will be a lot of bacterial contamination, which may or may not be a problem, depending on what you’re going to do with the DNA.
As a slight hijack (much as I hate to distract from the laser-like focus of the thread so far), I read a study about an interesting use of those infant blood spot cards. They were looking at a childhood leukemia associated with a certain chromosomal translocation. They found about a dozen kids that had developed this leukemia, and went back and tested their infant blood. In about two thirds of them, they found the translocation, meaning that they had actually acquired it in the womb, then later on in youth acquired some other insult that lead to active leukemia. I understand there’s now work going on to look for periods during gestation that leave fetuses unusually vulnerable to DNA damage. If enough evidence is found, the authors even suggested routine blood testig of all infants to see if they have DNA damage that could lead to cancer, so that they can keep a closer eye on them and catch any cancers earlier.
Anyway, back to poop.
Slight hijack:
I’m sorry to hear that about the buccal cells. We retrieve buccal cells for DNA on every homicide victim who has survived to be hospitalized, operated, and extensively transfused. And by extensively I mean massively - three times their own blood volume, for example. We feel the cheek cells are likelier to reflect the victim’s own DNA in that situation than their blood.
But I don’t know that any officer has yet had to call on the lab to obtain DNA from those cells yet, so I don’t know how well they do.
A mitigating factor may be that our patients are dead, and can’t feel pain, so we scrape like hell.
We also submit brain, liver, and kidney in varying stages of decomposition from fresh to yuck, and when it reaches yuck, relatively preserved muscle. We have also had to go to DNA from bone in skeletonized unknowns. These have gone to testing and have been successful in making identifications. Don’t know if the lab was doing mitochondrial DNA or went for nuclear DNA on deep bone samples.
I hope the forensic protocol works when you do it. I really hope so.
I knew about the children born with leukemia (commonest outside of Down syndrome is acute myelogenous leukemia, Philadelphia chromosome negative), but I hadn’t heard about the periods during gestation that would leave fetuses unusually vulnerable to DNA damage. That’s fascinating. I hate to ask “Cite?” when I’m not at all disagreeing with a poster, but can you remember roughly where you learned that? It sounds like something I should be up on… and would be really interested to know.
And, to un-hijack the thread, I totally agree with you and Vlad/Igor about the poop. Seems like most people are not aware their feces are 90% dead bacterial carcases. Until they go on antibiotics.
Really? I thought STR/PCR was the way of choice, moreso than RFLP, and that SNPs were becoming more frequently used as well! I guess I could be biased given that I’m a forensic chemist & the only time I’m really involved in DNA stuff is when I attend conferences, where everyone talks up the most recent techniques, but I’m certain that here in Australia we use STRs exclusively. I mean … hell … you guys don’t still use a Southern blot do you? 
What I understand of blood evidence is such:
[ul]
[li] Probably the first thing the crime scene investigators would do is a presumptive test on the stain on the knife to determine that it may be blood. This test is typically performed using a proprietary device such as the Hemastix, which is a slip of paper with a yellow chemical on the end. You swipe the yellow chemical bit over the stain, then add a drop of water. If the yellow bit turns dark green within a couple seconds, then your stain MIGHT be blood. There are lots of false positives (e.g. rust, tomatoes, etc. - the test works on the basis of chemical oxidation, which the haem part of haemoglobin performs if blood is present, but lots of other things can oxidate the chemical as well) but there really isn’t much scope for a false negative on a visible blood stain. Another possibility is the o-toluidine test, which involves 2 steps, and rules out some chemical oxidants, but still has false positives and is a more complicated process - it’s not really done much at the scene. Could be done at the lab, though.[/li][li] Determining that the blood is human probably is done by just DNA profiling. However, there are immunoassays such as the Ouchterlony test which also do this.[/li][li] Blood type is really easy, but not very helpful. However, there’s a lot of different antibodies being used for blood typing now so it’s not AS useless as it used to be. Combining things like A/B/O, Rh, and MN can get as specific as 10% of the population having that combination of antibodies. It can also hint at ethnicity in certain instances.[/li][li] If using a PCR-based profiling kit like Profiler Plus etc., you can get 13 to 16 locations on the genes to create a DNA profile. This is through STRs (“short tandem repeats”) which are areas outside of our genes (and thus more likely to vary) that have repeating, short units of DNA (e.g. CATTCATTCATT - I think that’s the TH01 locus). The number of repeating units in each locus is the distinguishing factor here. This can individualise blood to a 1-in-a-billion type accuracy, but of course it’s likely that two identical twins would produce the same DNA profile. This doesn’t tell you anything about the person though.[/li][li] Except for sex, because the amelogenin gene is one of the 13 or 16 loci being tested for. The amelogenin gene is 6 base pairs longer on the Y chromosome than on the X chromosome, thereby allowing us to determine sex.[/li][li] If you have a mixed profile (you can tell because you might get 3 or 4 answers for the same locus, when for a single person you should only get 2) and you are armed with some DNA from a relative of one of the two contributors, you can probably work out which profile is from which person.[/li][li] You could do a rough estimation of age, THEORETICALLY speaking, based upon the length of the telosome (the end part of the chromosome), as each time the DNA replicates the telosome is shortened slightly. However, I don’t think many crime labs would undertake this kind of complicated analysis. If your roleplaying scenario is in the CSI:NY world, they might! :)[/li][li] Foetal blood and infant blood may have a different type of haemoglobin (gamma?) but I’m not sure how long that sticks around.[/li][li] SNPs - pronounced “snips” but meaning Single Nucleotide Polymorphisms - find and identify single points in the genome where the DNA polymerase enzyme screwed up and put in the wrong base. Research is still assessing exactly how helpful this is, but in April I saw a very convincing presentation on the use of a smattering of SNPs to assign a racial group to the profile - caucasian vs south-east asian vs south-west asian vs african vs indigenous Australian, for example. The worst result was something like 60% accuracy for one of the racial groups, I think it was caucasian. SNPs may also be used to determine likely hair colour, eye colour, etc. - this is still in the early stages, but it’s developed enough that a crime lab with a fairly high-tech laboratory could potentially do this analysis or outsource it if the case was important enough and there was no other avenue for identfying the bloodstain.[/li][li] I don’t know if there would be much in the way of mitochondrial DNA (mtDNA) in a dried blood sample, but due to the abundance of mitochondria in normal cells (not present in red blood cells) mtDNA is often the easiest DNA to find in a degraded sample. mtDNA is identified by sequencing a section of the mt genome. mtDNA is maternally inherited so you can identify that a person is descended from a certain maternal heritage - e.g. link a son to his mother/grandmother/mother’s sister etc.[/li]
[li] Depending upon the amount of blood available you could possibly use an extraction method to attempt to isolate foreign drug substances and then identify them by GC/MS. Every forensic lab should have a GC/MS, it’s like we wouldn’t even exist without them! However - in my opinion - HPLC/MS/MS is a better method for detecting drugs in blood. I don’t know that it’s more sensitive per se, but it’s more flexible and customisable for the specific type of thing you’re looking for. Depending upon the size of the sample and the amount of drug that’s present, you might not be able to quantify it, but you could still be able to detect and identify it at low levels. Of course you have to screen for metabolites as well.[/li]
As for testing “for drugs”, you’re right in that you can’t just run one test to identify all possible drugs that may be in a person’s system. However, there are shorter “screening tests” you can do to determine whether drugs MAY be present. For example, there are colour tests which involve adding a chemical reagent or two to a drop of extract from the blood, and seeing if a colour change occurs. These are presumptive tests only but are very sensitive and rarely exhibit false negatives, especially in a laboratory setting.
You can divide the entire range of drugs up into a few classes - “acidic”, “basic”, and “neutral” tends to work well for analytical purposes - and then use a separatory technique (GC/HPLC/TLC) to look for the presence of each of these classes of drugs. If you find any indication that an acidic drug is present, for example, you can then perform another test to perfect your separation and determine which drug it is (usually by a spectroscopic detector, Mass Spectrometry being the most popular, but infrared spectrscopy works well also).
There are also immunoassay-based detection methods for drugs, but since they’re more biological than chemical, I don’t know much about them.
[li] If we’re talking just a knife, then blood spatter evidence wouldn’t really help much. It’s more useful in looking at a trail of blood droplets on a surface and determining the direction of the attack, the number of attacks made, and the type of weapon used when making the attack; whether a person was sitting or standing or lying down when they were attacked; etc. These can all be determined by simple trigonometric calculations.[/li][/ul]
Sorry for the length! If this was a more chemical-related question I could have babbled on even more than this. Kinda scary, huh? 
Hey, Caiata, do you work for private industry? Rufflups are cheap. I work for a state government. They hang onto old methods for a long time. Do what’s cheapest. We just year before last stopped using Windows 95. We squeeze every penny until it cries.
The telomere thing is a great idea. I’ve never seen it done, but who knows when the real world will catch up? One question: how close to age does it get you? You know forensic anthro tends to get you very close to age from birth to 13, within three years from 13 to 20, then by decades from 20 to 50, then “old” and “real old” from 50 on up. Do telomere lengths pinpoint your unknown’s age within a year, five years, a decade, or only narrow it down to first or final third of life?
Fetal hemoglobin is gone within three days of birth except in very rare circumstances (some of the thalassemia variants) which I’m sure you know about, but which aren’t helpful to the OP.
Yeah, I can’t offer up much about blood spatter to a role-playing game scenario that only wants to start with a bloody knife. But if he had wanted to start with a bloody scene!!!
And I’m still waiting to hear if there’s a body. What use is a blood-stained knife without a body?
All I can tell you is that I was researching a presentation I gave on the AML-ETO (8;21) translocation. It was in the one paper I ran across that was about fetal acquisition, and they just sort of casually mentioned that there was a theory out there about the possible existence of these periods. There was probably a footnote, but I didn’t follow it up.
I’m in a clinical lab, not a forensic one, but we still use Southerns for a couple of things. And the technology hasn’t changed at all - we still do it in Tupperware tubs, and we have a paper cutter to cut up the paper towels to put on top.
We’re currently in the process of upgrading our computer system from our old one. Which is DOS-based. From 1984. 
Is this a sure thing absolutely going to happen, or just possible?
It seems that privacy advocates would fight this tooth and nail.
Out of curiosity, do preemies maintain their fetal hemoglobin until term, or does it change after 3 days? If a baby needs a blood transfusion before they’re 3 days old, do they have to recieve infant blood with fetal hemoglobin, or can they use any old blood (type matched, of course) with “regular” hemoglobin?
I currently work for a government-run teaching facility, and let me tell you we certainly aren’t well-funded in the chemistry department (we don’t even have a GCMS, just a GC, what good is that?!?). However, I think there’s been a glut of funding here in Australia for DNA-based technology, because even our pathetic teaching lab has an autosequencer and several PCR machines. Our students, who have completed 4 units of Forensic Molecular Biology type courses, graduate without ever having run a Southern blot.
As for computers though, I know the Australian Federal Police still has some equipment that runs off a machine that actually has a TURBO button. You press it, and it switches the CPU from 20MHz to 66MHz. Wow, huh?
I’m not sure how far the research has advanced into this one - I imagine at this stage you can only get to the decade level, as you have to sort of guess how many times a cell would replicate over the course of a person’s life. Maybe real biologists know that, but I’m just a pseudo-biologist so I’m not sure However I think there’s room there for a really interesting addition to the forensic portfolio of DNA testing - if someone can get the statistics research done.
Hey, if a bloody scene ever comes up, you’ll be the first one I ask.
Well, that’s kind of what I wanted to know. There is a body, of course, but I haven’t quite decided where it is yet, and at any rate the players find the knife long before they find the body, if they ever do.
Smeghead wins.
Just possible. Just possible. However, it’s likelier to sneak in because there are pressing health reasons for making sure a sample is saved. Not only childhood leukemia and other blood dyscrasias to check for in the infant, but matching cord blood with its wealth of stem cells, to other children (and adults) who need urgent treatment for cancer. Also, my state (and many others) does a dried blood spot card on every infant to check for mitochondrial disorders (MCAD testing). They toss those cards out right now at six months if the tests come back normal, because they have so many of them. All it takes is a policy change to keep them forever.
Also, people tend to OK stuff happening for medical reasons to very tiny babies. You saw that Auntbeast got a dried sample with hers? Hear any outcry?
For that matter, hear any outcry at the national blood spot card filing program of the military? Even hear before that it existed? Ever hear of No More Unknown Soldiers?
I know it’s a step (and an opportunity for privacy advocates) from blood spot card filing to karyotyping, but as the technology gets quicker and cheaper, the step gets shorter and faster.
I’m willing to predict there will be national blood spot card filing in the next twenty years, and karyotyping before I retire. Ten dollars on that to any Doper who wants to take me up on it.
The proportion of fetal hemoglobin to regular hemoglobin declines very rapidly. Like anything in the body, it’s not an all-or-none switch. Red cells filled with mostly mature hemoglobin start appearing rapidly and take over.
Children who need transfusions in the womb (erythroblastosis fetalis, fetal-maternal blood loss victims) are transfused with regular banked blood. Where are we gonna get fetal blood, vampire it off some other fetus through the pregnant woman’s belly? I don’t think so.
Fetal hemoglobin is different only because it hangs on to oxygen a little longer and gives it up in oxygen-poorer environments than regular hemoglobin. Which figures, if you think about the womb setup.
OK, the Australian Federal Police win. Smeghead, take note.
If the bloody knife is found in the same room where the killing was done, there’ll be spatter.
If not, hack away!
You do ask the weirdest questions. I am so grateful they give me an opportunity to pontificate. I wonder sometimes about the RPG you’re writing, what it’s like. I bet you’re having fun.
I bet the people who play the RPG will be having fun soon, too.