[remotemass (OP)]

Of course, genetic code sequencing is still quite expensive but let's say that you have a million drops of blood from different individuals from city A and as they arrive one by one at city B, you would have to predict/identify with great accuracy the individual that has just arrived recently taking new blood from him and comparing it to the million of other samples.
What would be the most affordable way that was quite reliable and accurate at least to make a very good triage of it all? What chemicals or markers would you be looking at? Could sucrose levels or sodium chloride levels help or even be good enough to be considered sufficient?

[alancalverd]

The DNA test will pretty well identify an individual with odds of misidentification lower than 1:1,000,000, but if you want to know how long he has lived in a particular area, you'd need to look at the isotopic constitution of his teeth or bones, and that is diet-dependent, changes very slowly, and may not distinguish between modern urban environments where food and water may originate from a long way away!.

Sucrose and electrolyte levels vary from minute to minute. At best, you might suspect that your target is diabetic or addicted to "energy drinks" - or maybe just likes salt on his chips.   

[Bored chemist]

Disney use fingerprinting to make sure you don't pass your multi-day ticket to someone else.

[evan_au]

The first case where DNA sequencing played a major role in identifying the killer was a serial killer called the "Golden State Killer".
- The police had DNA samples from the crime scenes. This is ennough to confirm a suspect is or is not the criminal.
- However, in this case, there was no suspect, and this man did not have his DNA on record, so the police couldn't find an exact match
- However, public DNA databases (Ancestry.com, 21andme etc) did have DNA checks on several third cousins - and also family trees, so the police could easily spot people with the right amount of relatedness
- They found a man with an exact match on their second guess.
- These DNA sites don't do a complete DNA sequence, but instead use short sections of DNA that have many variants in the community (some of them selected because they have been linked to risk for some disease, or because they are indicative of certain ancestor population groups)
- The more points of comparison, the more likely that you can find a match
https://en.wikipedia.org/wiki/Single-nucleotide_polymorphism
https://www.forbes.com/sites/jvchamary/2020/06/30/genetic-genealogy-golden-state-killer/?sh=49433be95a6d

[JenniferZigler]

So much theory and no figure. So, what is the approximate price, pls?

[alancalverd]

Around $300, according to the internet.

[thugtomas]

Principles of Bloodstain Pattern Analysis. To understand how analysts interpret bloodstains, one must first understand the basic properties of blood.

[Bored chemist]

Around $300, according to the internet.

Looks like fingerprinting is a lot cheaper.

[alancalverd]

And quicker. Just a bit less precise in practice: you can reasonably re-identify Joe Bloggs if you have his previous dabs and reason to suspect the new ones are his, but without good specimens you might be hard pushed to distinguish Bloggs from any number of Smiths if you only have partials or smudged prints.

[evan_au]

$300 is the cost of a genetic test, if done in bulk on pure samples of significant size.
- However, in forensic work, the perpetrator's DNA is often mixed with that of the victim, or spread thinly on surfaces already contaminated by other people. This requires careful extraction of multiple samples, and complicates the analysis considerably.
- The samples need to be collected, stored, processed and the results analysed in a rigorous and traceable manner, which will be cross-examined in court
- It gets a whole lot more complicated if you don't already have a DNA sample from the perpetrator in your database
- You could guess a forensic cost from thousands of dollars to ten times that amount.

However, unlike fingerprinting, if you have a relative of the perpetrator in the database, you can identify the link, and zero in on the identity of the perpetrator.

[JenniferZigler]

Around $300, according to the internet.

OMG, a considerable one. Thanks for precising*

[Bored chemist]

This scenario

say that you have a million drops of blood from different individuals from city A and as they arrive one by one at city B,

looks to me like

you can reasonably re-identify Joe Bloggs if you have his previous dabs and reason to suspect the new ones are his,

[Deecart]

Around $300, according to the internet.

In UK perhaps (even some covid test was so expensive).
Normaly, actually full genetic sequencing (not only some test) cost around 100 euros.

First sequencing costs 3 billions euros and many years.
2007 cost is 1 million and 3 months.
2013 cost is 1000 euros and some hour.
Today, 100 euros (dollars) and some minutes.
One of the best provider (there are some others in China) : https://www.ultimagenomics.com/