raisincharlie said:
Hello DD,
I would be interested in knowing what this person thinks of the YSTR DNA analysis and its usefulness with respect to criminal cases. How many markers can they match up in a mixture ? If he laughs it is because I'm a dufus and haven't asked this correctly. Thanks for the opportunity to ask !
Happy Valentine's Day, RC! My DNA guru came through already today...here's his answer re YSTR DNA:
"Y-Str analysis is very useful in criminal cases because it only gets a DNA profile from male DNA (the y chromosome is what makes us male). That's important because with autosomal str analysis (which is the normal DNA typing) you have something called competition. What that means is that during one of our steps called amplification (that's where we make millions and millions of copies of only the DNA we want to look at), all DNA in a sample will be amplified (or copied) proportionally. So, as the DNA from the suspect is being copied, so is the DNA from the victim (and in many cases-particularly sexual assaults-the victim is female.)
With Y-str analysis, you don't have to worry about the female DNA because you are only copying and looking at the male DNA. My belief is that this is mostly useful in cases where the suspect and victim are male and female. Every paternally-related male will have the same Y-str profile (which is not true for the normal autosomal str profile, which only identical twins will share). In other words, I have the same Y-str profile as my father, his father, his brothers, any of my brothers, etc. This isn't very discriminating when relatives are involved, as you can see. When you add more than one contributor to the mix, it gets really complicated.
In fact, during a validation study of Y-str looking at mixtures, one of our Lab directos could not be excluded as a possible contributor - and he didn't even give one of the samples.
So in my opinion, I think that Y-strs are primarily useful in single source male samples. I think (for now) that trying to interpret mixture Y-str profiles and include possible perpetrators is not erring on the side of caution or conservatism and is basically going out on a limb (which we DON'T want to do). In fact, THE scientific working group in the US that comes up with suggested guidelines and protocols (which basically every single accredited DNA lab follows) has not published a comment on this matter of mixtures yet."
Did that answer your question, RC? (I did notice he didn't answer the specific question re how many markers).
He said he'd be GLAD (!!!!) to answer more questions and might be able to better explain with some visuals :crazy: He told me "anytime." So, I may cruise by the lab sometime early next week...wanna come visit Central TX for a lab tour and see it for yourself?
I did also ask one question I had, and here's his answer:
Q - Re lab backlogs. If we (LE) have a hot or high profile murder case and need lab testing, do they "bump" lab testing requests already backlogged or ? Just how are priorities set, other than date of receipt in the lab?
A: "There is a lot of bumping. In our lab, child-victim cases, elderly-victim cases, murder cases, and cases with court dates receive priority. I think you also have to assess public threat. A serial rapist case will receive higher priority over a case where a victim goes to a party, gets drunk, passes out, and THINKS her friend may have raped her, but she isn't sure. So basically, we take all of the above into consideration and try to work the cases accordingly."
Interestin that he mentioned assessing public threat.
FWIW. Hey, I learned about Y-str DNA, of which I had never heard of until you mentioned it. Pretty neat. Thanks!
