Menstrual blood also does not clot the way other blood does.
That’s because it already clotted, before it was shed. But if other blood has been sitting around for a while, the same might be true of it.
Some menstrual blood clots first, but most of it does not.
I have almost 40 years of personal experience with this.
There have been endless TV dramas and real life crimes where DNA evidence indicated more than one human involved. (Blood - but same for semen samples).
I assume it’s not down to “this DNA belongs to A, this belongs to B”, but more as “This person has DNA compatible with one of persons in the mix sample.” (Unless it’s a mix of male and female, then the Y is specific to the male and he will match one of the three X’s.)
I should add that if the blood sample is a mix of say, the assailant and the victim, then by testing the victim’s blood separately from a different (clean) sample I assume they can say what the “extra” DNA belonging to the other person is.
Blood doesn’t mix at the cellular level. Yes, two distinct DNA profiles would be devloped.
This says that camels don’t have nucleated blood cells. I wonder which is correct?
Poking around I think the enucleated side is what is supported 
. I learned that little factoid probably circa 1987 from an already nearly retired Natural History professor who got his PhD in the 1950’s and did NOT work on mammals. I’m a little surprised it’s wrong, but I suppose I can’t be shocked.
Learn something new every day!
It was fascinating to learn about mammal vs non-mammal RBCs, and the oval shape of camelids’ RBCs due to desert adaptations allowing swelling and shrinking along with de/hydration. Thanks for posting it!
IIRC, not a biologist, but I think it goes something like this:
The DNA profile is accomplished by using particular chemicals to explicitly snip DNA at certain points. The resulting fragments are then put into a photochemical process to determine the mass of each of those resulting fragments. Different DNA from different people has slightly different weights. So instead of getting “this particular piece of DNA is a 12” you get “for this particular DNA segment, we get a 12 and a 15”. Analyze enough different segments, the odds of a person matching precisely begin to reach astronomical proportions. The odds of a person’s DNA segments matching one of two numbers is a lot less likely, but still in the realm where an exact match is so unlikely as to be extremely unlikely in a population of only 8 billion people.
And remember, in a criminal case - you aren’t getting a DNA profile, then combing the entire population for anyone who matches - you have one or a pool of maybe a dozen or so suspects who have motive and opportunity, and want to see if they match.
It occurred to me that if I wanted to hide a murder, I’d commit it in a slaughterhouse.
You’d have to have some SIGNIFICANT suspicion about that particular splash of blood on the abattoir
floor being human instead of pig or cow.
It also occurred to me…I’m not the first guy to wonder that.
Instead of waiting days or weeks for the lab to return DNA results, could the various CSI Techs have available some quantity of Human Specific Antigen which could provide a (near) immediate reaction to human specific proteins found in blood?
Never worked there, but it seems to me that the number one job in any facility where animals are slaughtered (or butcher shops where meat is chopped up ) is - clean, clean, CLEAN!
Any residue that remains for more than a day is going to create a god-awful stink. Even with good cleaning, many slaughterhouses do ot have the outdoor fresh fragrance of an freshly mowed field.