Some preliminary comments. My "expert" will remain unidentified, except to reveal she's female. She is not famous, she does not serve as an expert witness in court - though she could. She does DNA testing on a daily basis, so presumably she knows quite a bit about it.
A second point - I don't know squat about dna, or any other scientific stuff, so there's really no point arguing with me if you disagree with anything I'm going to say. My only possible response is "That's what I was told". I'm just a reporter. (and not even a science reporter)
A final preliminary matter - my expert doesn't know anything about legal standards of evidence admissability. She's just giving me the scientific point of view.
This is what I was told.
1. There is no male/female dna. IOW, a sample of dna can't reveal whether it was from a man or a woman. Think of it somewhat like fingerprint lines - unique to the individual, but not M/F. My expert did say that chromosomes could reveal M/F origin, but not dna. So, all this business about male dna being left in the panties/longjohns is not proven. We know it's a match, but we don't know if it's male or female.
2. DNA does not degrade over time. Cells degrade, but the dna is still intact. My expert said she could analyze a sample 1000 years old, if you have one. Which brings us to markers.
3. My expert had no idea what I was talking about when I asked about markers. She said chromosomes have markers, but not dna. I asked if maybe the bands were being called markers, and she said she tought that might be what non-scientists were talking about. In her opinion, it wouldn't matter how many bands were present, she could say yes/no as to a match.
We learned from Brent Turvey last night that as few as 7 markers have been sufficient to go to court (whatever a marker is)
4. Sample size is not an isssue. She laughed about the distinction between lcn and "normal" dna sample sizes and tests. She said she could do a test with one cell. She said in the field they've been able to amplify a sample that small and analyze it for about 30 years, so she didn't really know what was supposed to be "new" about this lcn test.
Since sample size (one cell or more) isn't an issue in gettng a match, she said that there was no way to determine whether the sample from the longjohns was "big" based on it being run as a "normal" test. One cell is all it takes.
5. Someone knows whether the panty dna was semen, blood, or saliva. She said they'd be able to tell from other material in the cell what sort of liquid it came from.
6. The three dna samples could have got there by some inocent transfer. My expert saw no reason to conclude that the dna had to be from the killer, or was even highly likely to be from the killer. She didn't think the liquid/skin cell dichotomy mattered much, as only one cell is required for anlaysis (though typically there is more than that), and there are many scenarios by which both liquid and skin could transfer - sneezing, coughing, wiping her down after going to the bathroom, can all cause a liquid transfer and at the same time skin cell transfer. Again, there needn't have been any "large" sample present - a 3 point match requires only 3 cells.
I think that is all I asked her about. If I remember anything else I'll add it in another post.
Again, I want to point out that my expert knows how to work with DNA, but not about courts standards of admisibility or how to present the evidence to a jury.
A second point - I don't know squat about dna, or any other scientific stuff, so there's really no point arguing with me if you disagree with anything I'm going to say. My only possible response is "That's what I was told". I'm just a reporter. (and not even a science reporter)
A final preliminary matter - my expert doesn't know anything about legal standards of evidence admissability. She's just giving me the scientific point of view.
This is what I was told.
1. There is no male/female dna. IOW, a sample of dna can't reveal whether it was from a man or a woman. Think of it somewhat like fingerprint lines - unique to the individual, but not M/F. My expert did say that chromosomes could reveal M/F origin, but not dna. So, all this business about male dna being left in the panties/longjohns is not proven. We know it's a match, but we don't know if it's male or female.
2. DNA does not degrade over time. Cells degrade, but the dna is still intact. My expert said she could analyze a sample 1000 years old, if you have one. Which brings us to markers.
3. My expert had no idea what I was talking about when I asked about markers. She said chromosomes have markers, but not dna. I asked if maybe the bands were being called markers, and she said she tought that might be what non-scientists were talking about. In her opinion, it wouldn't matter how many bands were present, she could say yes/no as to a match.
We learned from Brent Turvey last night that as few as 7 markers have been sufficient to go to court (whatever a marker is)
4. Sample size is not an isssue. She laughed about the distinction between lcn and "normal" dna sample sizes and tests. She said she could do a test with one cell. She said in the field they've been able to amplify a sample that small and analyze it for about 30 years, so she didn't really know what was supposed to be "new" about this lcn test.
Since sample size (one cell or more) isn't an issue in gettng a match, she said that there was no way to determine whether the sample from the longjohns was "big" based on it being run as a "normal" test. One cell is all it takes.
5. Someone knows whether the panty dna was semen, blood, or saliva. She said they'd be able to tell from other material in the cell what sort of liquid it came from.
6. The three dna samples could have got there by some inocent transfer. My expert saw no reason to conclude that the dna had to be from the killer, or was even highly likely to be from the killer. She didn't think the liquid/skin cell dichotomy mattered much, as only one cell is required for anlaysis (though typically there is more than that), and there are many scenarios by which both liquid and skin could transfer - sneezing, coughing, wiping her down after going to the bathroom, can all cause a liquid transfer and at the same time skin cell transfer. Again, there needn't have been any "large" sample present - a 3 point match requires only 3 cells.
I think that is all I asked her about. If I remember anything else I'll add it in another post.
Again, I want to point out that my expert knows how to work with DNA, but not about courts standards of admisibility or how to present the evidence to a jury.