You raise some interesting questions, and unfortunately, the answers are complex and lengthy.
TL;DR: the word "profile" is not precise or scientific; it is a tool - like alphabetization or use of letters to denote sounds.
The very word "profile" is the problem.
Human DNA is 99.5% the same as chimp DNA. Humans are 50% the same, genetically, as bananas.
The word "profile" is used to denote the process by which geneticists study the relevant part of the DNA. It's silly and useless to use the part we share with so many life forms (fruit flies, palm trees, cows, etc). Instead, we look only at the...parts that make us human. We do not profile bananas in order to find a human, obviously (that is supposed to be funny, I realize this is kind of dry).
A FULL DNA sample would contain 50-300 million separate base pairs. But we don't need all of those in order to make a match - we need the parts that are specific to humans. When the lab looked at the DNA, they likely chose to look at...the base pairs associated with being human. Further, there are sets of base pairs (we can call them SNP's when we are talking about variation in a base pair) that have a lot of variation. THAT is what we have to look at.
If humans are 99.5% the same as chimps, we need to study ONLY the specific parts of the genome that relate first to...being human and then to being a
human individual. Some base pairs have tremendous variation (hemoglobin for example - has about 600 variants in just one base pair). If we look at hemoglobin variation closely, we can see that once upon a time we had hemoglobin similar to that of chimps, but our line had an early mutation (maybe 6 million years ago) that then spread through out the genus *advertiser censored* (to ergaster, erectus, habilis, etc) - so we share some of those markers with them. However, we have tremendous variation at that one location.
One set of SNP's is not enough to make a match. What is wanted is for ALL of the relevant SNP's in the sample to match another sample (in this case BK's full DNA - which is what we get with a cheek swab). The lab said it was "single source" DNA, which means that all of the bits of DNA on the sheath came from the same person (the various strands were tested against each other to see if it was one person or more than one person). That means the lab had plenty of SNP's to make that determination. Indeed, it seemed to me at the time that they had entire chromosomes. I don't think a determination of "single source" (or sex of the contributor) can be made without complete chromosomes (or relatively complete). Did they have his ENTIRE set of genes on that sheath? We don't know. What they did find was sufficient DNA to conduct the legally admissible STR analysis (which is not considered profiling in the way that SNP analysis is a sampled profile - a profile just means "consistent sampling technique" in DNA labwork).
To sum up, we do not look at 300,000,000 variant base pairs when we find the specific SNP's that denote H. sapiens. We look at the genes that make us human. So that's 0.5% of 300,000,000. Does the public want banana analysis added back in? I don't think so. We can deduce ethnicity from facts surrounding whether there is much variation within the given sample (so, some people do NOT have 300,000,000 varying base pairs - they have far fewer, only 50,000,000). This occurs due to inbreeding coefficients in isolated places (so for example, my non-European ancestors include populations where there is much less genetic variation than in Europe, whereas my European ancestors have much more variation, especially after arriving in the Americas).
What the lab did was compare the valuable SNP's in the sample, sufficient in number to make the analysis, with an online genetic database.
What the Defense is asking for has nothing to do with profiles or sampling. They know that's been done in the standard, worldwide-accepted scientific manner. What is going on is the questioning of the IGG process.
I would say that it's somewhat like requiring the phone company to explain and divulge how they got the numbers in the phone book. It's such a wierd (and naive?) question that most experts in phone analysis would just stare in disbelief. "We are the phone company; we issue the numbers to a person who has given us some proof of name and identity, we simply print it out and put it in a book - so that people can look up each others' phone numbers!"
IGG is a big phone book, with identities, of DNA.
-- Of the trillions of cells that compose our body, from neurons that relay signals throughout the brain to immune cells that help defend our bodies from constant external assault, almost every one contains the same 3 billion DNA base pairs that make up the human genome – the entirety of our...
sitn.hms.harvard.edu
Investigators found a knife sheath near one of the victims which contained the microscopic clue.
www.krem.com
and for more about our similarity to bananas, this is a good piece:
We’ve long known that we’re closely related to chimpanzees and other primates, but did you know that humans also share more than half of our genetic material with chickens, fruit flies, and bananas?
www.pfizer.com
Most anthropological geneticists say that there are only 1000-1500 genes that actually distinguish humans from other close species. That's what we're looking at in forensic analysis, unless we think a chimp did it (which would be pretty obvious if it was chimp DNA). Is that a profile? The press uses the word loosely. It is not merely a "sample" - it's the core of our biological identity, the roots of the human genomic tree.
