Reply
 
Thread Tools Display Modes
  #1  
Old 05-21-2020, 10:34 PM
MorrisCody is offline
Guest
 
Join Date: Mar 2012
Posts: 59

Writing a story: How would an amateur amplify a DNA sample at home?


I'm helping a friend with a story they're writing that features an amateur detective. She has found a clue that has a potential suspect's DNA on it, and she wants to turn a little bit of DNA into a lot of DNA. How could she go about this?

Last edited by MorrisCody; 05-21-2020 at 10:35 PM.
  #2  
Old 05-21-2020, 10:40 PM
markn+ is offline
Guest
 
Join Date: Feb 2015
Location: unknown; Speed: exactly 0
Posts: 3,318
By using the Polymerase chain reaction. I have no idea how easy it would be for an amateur to obtain the necessary tools and chemicals.
  #3  
Old 05-21-2020, 11:09 PM
Dr. Strangelove's Avatar
Dr. Strangelove is offline
Guest
 
Join Date: Dec 2010
Posts: 8,524
You can just buy PCR machines on the cheap these days. Or build one yourself from parts. They aren't that complicated.
  #4  
Old 05-21-2020, 11:15 PM
Riemann's Avatar
Riemann is offline
Guest
 
Join Date: Nov 2015
Location: Santa Fe, NM, USA
Posts: 8,467
You don't need a PCR machine to do PCR. All it actually does is raise and lower the temperature in cycles. You can do it manually with water baths, that's how it was done originally.

But PCR will only amplify specific short segments of DNA, not entire genomes.

OP, a little more info is needed. What exactly does she plan to do with the large quantity of DNA?
  #5  
Old 05-22-2020, 12:44 AM
Melbourne is offline
Guest
 
Join Date: Nov 2009
Posts: 6,313
Quote:
Originally Posted by MorrisCody View Post
I'm helping a friend with a story they're writing that features an amateur detective. She has found a clue that has a potential suspect's DNA on it, and she wants to turn a little bit of DNA into a lot of DNA. How could she go about this?
I think you don't do it that way. You test the small sample of degraded DNA using a very sensitive (amplifying) PCR test, but you don't get "more DNA" as part of the process.

I could be wrong.

And I would think of testing the small degraded sample by sending it off to a test lab. The problem with "sending it off to a lab" is that unless it's a dedicated forensics lab you don't maintain a chain of evidence by doing that, but I hope that doing it myself would be open to the same objections.
  #6  
Old 05-22-2020, 12:57 AM
steepone is offline
Guest
 
Join Date: Aug 2016
Location: Western Australia
Posts: 110
IANAL but wouldn't the fact that this amateur detective collected and handled the DNA mean it could no longer be used as evidence in any case
  #7  
Old 05-22-2020, 03:11 AM
MorrisCody is offline
Guest
 
Join Date: Mar 2012
Posts: 59
Wow, who'd've thunk amplifying DNA would be so complicated?

The objective of the detective (hey, that rhymes) in the story* is to obtain a sample of the suspect's DNA, amplify the appropriate segments, put the solution into a spray bottle and plant the DNA all over town for the police to find and analyze.

*I am really over simplifying the story, because the long plot explanation is, well, long. Also, if I give it away, then someone is likely to steal the plot, and this book by a middle-aged, first-time author who just got laid off from her accounting job is guaranteed to outsell the bible. (I'm talking cumulative sales.) A good analogy would be to something that happened to me in high school: Someone posted really racist flyers around campus, and nobody was allowed to leave the ensuing assembly until the guilty party came forward. After about 90 minutes of sitting in silence, the absolute sweetest girl in the school admitted she'd done it. It took about two minutes for the real culprit stepped forward, because he couldn't let this girl take the blame for what he'd done.
  #8  
Old 05-22-2020, 05:08 AM
Riemann's Avatar
Riemann is offline
Guest
 
Join Date: Nov 2015
Location: Santa Fe, NM, USA
Posts: 8,467
This is not within the capabilities of an amateur. It doesn't need advanced skills or experience specifically with forensics, but you'd need basic technical skills and access to some basic lab kit - I think your protagonist needs to be in cahoots with a grad student at a university lab or something.

CODIS DNA profiling analyzes 20 standard loci. So one approach would be to PCR amplify just these loci. You could dilute and plant these fragments, and a standard CODIS analysis would amplify off the fragments, making it appear for the purposes of the basic CODIS protocol that the suspect's genomic DNA were present. With this method, if suspicion arose, it would be easy to do other tests (attempt PCR amplification of any other part of the genome) to prove that only the CODIS loci are present in the sample, and not genomic DNA - this could be a plot point to prove the plant. The 20 CODIS loci are published information, there are standard kits you can buy with the required primers, and information on protocols is publicly available. Here's the main NIST page:
https://strbase.nist.gov/

The (possibly more straightforward) alternative would be Whole Genome Amplification, which again requires some basic skills and access to lab equipment, but commercial kits are available, so any competent grad student with access to a lab (but not an amateur) could figure out how to do it.
https://journals.plos.org/plosone/ar...l.pone.0171566
https://www.qiagen.com/us/service-an...erview-on-wga/
This method would be more robust to forensic detection if the plant were suspected.

Last edited by Riemann; 05-22-2020 at 05:10 AM.
  #9  
Old 05-22-2020, 05:22 AM
Riemann's Avatar
Riemann is offline
Guest
 
Join Date: Nov 2015
Location: Santa Fe, NM, USA
Posts: 8,467
To add - I don't have specific experience with forensics, but forensic samples have tiny amounts of DNA. If you wanted a plot point that the "plant" is detected, one interesting way might be that the forensic test looks odd because after the amplification your protagonist made the mistake of not diluting enough, so that far too much DNA is present. But you'd need to talk to somebody in forensics if you wanted something really technically authentic here.
  #10  
Old 05-22-2020, 05:22 AM
Bullitt's Avatar
Bullitt is offline
Member
 
Join Date: Apr 2012
Location: SF Giants Nation 10-12-14
Posts: 27,570
Quote:
Originally Posted by Riemann View Post
This is not within the capabilities of an amateur. It doesn't need advanced skills or experience specifically with forensics, but you'd need basic technical skills and access to some basic lab kit - I think your protagonist needs to be in cahoots with a grad student at a university lab or something.

CODIS DNA profiling analyzes 20 standard loci. So one approach would be to PCR amplify just these loci. You could dilute and plant these fragments, and a standard CODIS analysis would amplify off the fragments, making it appear for the purposes of the basic CODIS protocol that the suspect's genomic DNA were present. With this method, if suspicion arose, it would be easy to do other tests (attempt PCR amplification of any other part of the genome) to prove that only the CODIS loci are present in the sample, and not genomic DNA - this could be a plot point to prove the plant. The 20 CODIS loci are published information, there are standard kits you can buy with the required primers, and information on protocols is publicly available. Here's the main NIST page:
https://strbase.nist.gov/

The (possibly more straightforward) alternative would be Whole Genome Amplification, which again requires some basic skills and access to lab equipment, but commercial kits are available, so any competent grad student with access to a lab (but not an amateur) could figure out how to do it.
https://journals.plos.org/plosone/ar...l.pone.0171566
https://www.qiagen.com/us/service-an...erview-on-wga/
This method would be more robust to forensic detection if the plant were suspected.
Correct -- not within the capabilities of an amateur. But an amateur with the right connections, and it can easily happen.

As a software test engineer, one of my previous jobs about 15 years ago was working for Applied Biosystems on one of their PCR machines -- the software that drove the amplification machine. A software tester, or software developer, or product manager working at such a company would have access to the chemicals and equipment and, talking to a friend at work who understands PCR, could do the amplification.

For PCR amplification, I'm definitely an amateur. I worked there about one year and never again got back into that field.

I never did it, but theoretically I'm certain it could happen this way.
  #11  
Old 05-22-2020, 05:24 AM
Bullitt's Avatar
Bullitt is offline
Member
 
Join Date: Apr 2012
Location: SF Giants Nation 10-12-14
Posts: 27,570
Quote:
Originally Posted by Riemann View Post
To add - I don't have specific experience with forensics, but forensic samples have tiny amounts of DNA. If you wanted a plot point that the "plant" is detected, one interesting way might be that the forensic test looks odd because after the amplification your protagonist made the mistake of not diluting enough, so that far too much DNA is present. But you'd need to talk to somebody in forensics if you wanted something really technically authentic here.
In my scenario, the sample collecting and forensics skills is a key missing link.


ETA: and just now looking it up, I see that Kary Mullis passed away last August at 74 years old. He was the father of PCR, and he won the Nobel Prize for it. Not bad for a guy, while high and stoned, gets the inspiration for the idea that becomes PCR. Or is that a myth?

Last edited by Bullitt; 05-22-2020 at 05:28 AM.
  #12  
Old 05-22-2020, 05:28 AM
MorrisCody is offline
Guest
 
Join Date: Mar 2012
Posts: 59
Quote:
Originally Posted by Riemann View Post
This is not within the capabilities of an amateur..
Thank you. Everything you wrote is extremely helpful.
  #13  
Old 05-22-2020, 06:09 AM
Darren Garrison's Avatar
Darren Garrison is offline
Guest
 
Join Date: Oct 2016
Posts: 13,910
Quote:
Originally Posted by Melbourne View Post
I think you don't do it that way. You test the small sample of degraded DNA using a very sensitive (amplifying) PCR test, but you don't get "more DNA" as part of the process.

I could be wrong.
You are. Getting more DNA is the whole purpose of PCR.
  #14  
Old 05-22-2020, 06:11 AM
Riemann's Avatar
Riemann is offline
Guest
 
Join Date: Nov 2015
Location: Santa Fe, NM, USA
Posts: 8,467
Quote:
Originally Posted by Bullitt View Post
ETA: and just now looking it up, I see that Kary Mullis passed away last August at 74 years old. He was the father of PCR, and he won the Nobel Prize for it. Not bad for a guy, while high and stoned, gets the inspiration for the idea that becomes PCR. Or is that a myth?
I don't know, but he apparently lacked the ability to reliably distinguish groundbreaking scientific inspiration from pseudoscientific fantasy. He notoriously went off the deep end later in life - with climate change denial, HIV-AIDS denial, conspiracy theories.
  #15  
Old 05-22-2020, 06:12 AM
Sparky812 is offline
Member
 
Join Date: Aug 1999
Location: Great White North
Posts: 4,779
Quote:
Originally Posted by MorrisCody View Post
Wow, who'd've thunk amplifying DNA would be so complicated?

The objective of the detective (hey, that rhymes) in the story* is to obtain a sample of the suspect's DNA, amplify the appropriate segments, put the solution into a spray bottle and plant the DNA all over town for the police to find and analyze.
Why would they need to amplify it? Couldn't they just collect the suspect's DNA from some bodily fluids, dilute it, and spread it around?
  #16  
Old 05-22-2020, 06:19 AM
Bullitt's Avatar
Bullitt is offline
Member
 
Join Date: Apr 2012
Location: SF Giants Nation 10-12-14
Posts: 27,570
Quote:
Originally Posted by Riemann View Post
I don't know, but he apparently lacked the ability to reliably distinguish groundbreaking scientific inspiration from pseudoscientific fantasy. He notoriously went off the deep end later in life - with climate change denial, HIV-AIDS denial, conspiracy theories.
What a nut case. But, hey, without PCR we wouldn't have all the DNA evidence-based cases being solved. Or bodies being identified in other tragedies.
  #17  
Old 05-22-2020, 06:43 AM
Paul in Qatar is offline
Guest
 
Join Date: Jul 2002
Location: Dammam, Saudi Arabia
Posts: 13,447
In a work of fiction, you would send it to a fictional company that let's you take degraded DNA from a long-dead relative and analyze it for genealogical research.
__________________
800-237-5055
Shrine Hospitals for Children (North America)
Never any fee
Do you know a child in need?
  #18  
Old 05-22-2020, 08:18 AM
Chronos's Avatar
Chronos is offline
Charter Member
Moderator
 
Join Date: Jan 2000
Location: The Land of Cleves
Posts: 88,635
We were doing PCR in high school, within a year after it was discovered. While it does take special skills and chemicals, those skills and chemicals are not at all hard to come by. It'd be an extremely weird hobby, but it requires considerably less specializations than a number of other real hobbies.
  #19  
Old 05-22-2020, 08:34 AM
Jackmannii's Avatar
Jackmannii is offline
Guest
 
Join Date: Oct 2000
Location: the extreme center
Posts: 33,400
Quote:
Originally Posted by Sparky812 View Post
Why would they need to amplify it? Couldn't they just collect the suspect's DNA from some bodily fluids, dilute it, and spread it around?
DNA "planting" has been used as a fictional plot device - i.e. getting hold of a used condom. You wouldn't need to dilute the sample, as highly sensitive detection methods can pick up minute amounts of DNA* (not sure why the OP's plot would require the DNA to be spread "all over town"). One (of many) problems with amateur PCR is avoiding contamination, difficult if one is not experienced with amplification protocols.

I suppose this could be worked into the plot, but it would probably look highly suspicious if "planted" DNA consisted of heavily amplified short segments of a genome, rather than the whole DNA techs are used to working with.

*see "touch" DNA.
  #20  
Old 05-22-2020, 09:46 AM
md2000 is offline
Guest
 
Join Date: Feb 2009
Posts: 15,651
The other problem is - so what?

You amplify segments of the DNA and plant them. The forensics team investigating likely does their routine work and does not notice the sample has been pre-sliced into analyzable segments.

(Plot twist - the forensics lab analyzes a few segments, IIRC about 16. Can yo fake a profile by selecting a segment from here, a segment from there, and mixing them together so it matches a third party? Can you sprinkle random segments to make the guilty party look like someone - or someones - else?)

Otherwise, you have your amplified DNA sample. Then what? The next step is electrophoresis(?) to get the profile and those classic series of lines, so this is another technical process our Nancy Drew needs to master. And some other profile to compare it to...
  #21  
Old 05-22-2020, 09:51 AM
Chronos's Avatar
Chronos is offline
Charter Member
Moderator
 
Join Date: Jan 2000
Location: The Land of Cleves
Posts: 88,635
While gel electrophoresis used to be the standard way to get a "DNA fingerprint", I think nowadays it's more often done by sequencing, which provides more information.
  #22  
Old 05-22-2020, 10:11 AM
Riemann's Avatar
Riemann is offline
Guest
 
Join Date: Nov 2015
Location: Santa Fe, NM, USA
Posts: 8,467
Quote:
Originally Posted by md2000 View Post
Plot twist - the forensics lab analyzes a few segments, IIRC about 16. Can yo fake a profile by selecting a segment from here, a segment from there, and mixing them together so it matches a third party? Can you sprinkle random segments to make the guilty party look like someone - or someones - else?
To fake someone's DNA, you need to know their DNA profile. So the scenario would have to be that you know their profile from seeing the results of a forensic analysis, but you don't have access to their sample.

20 loci are used in the U.S. (CODIS). There are only a few different alleles in the population at each locus, the power comes from the large number of loci. So if you had samples from a bunch of random people (my guess is something like a few hundred) you would cover most of the variation present in the population. From this "library" of samples you could selectively amplify each locus from a person who matches your target at that one locus. Then mix the products together, and you've got 20 segments that would simulate a DNA sample from your target. If a few loci were not available in your library, that wouldn't matter - not all loci always amplify in forensic testing, because the DNA sample is degraded.

As I mentioned above, the presence of just segments from the 20 CODIS loci (rather than genomic DNA) would work only if there were no grounds for suspicion, if the lab just ran the routine DNA profiling reaction. If they did suspect, it would be easy to show that genomic DNA was not present by simply attempting to amplify any other parts of the genome.

Last edited by Riemann; 05-22-2020 at 10:12 AM.
  #23  
Old 05-22-2020, 11:44 AM
md2000 is offline
Guest
 
Join Date: Feb 2009
Posts: 15,651
So can a lab actually separate out samples from multiple people? (The classic "she had sex with 3 different people")? or does it all get processed mixed together, so if #1 has a 2 and an 8, #2 has a 3,4,and 6, #3 has a 4,12, 18 and #4 has 2 and 9... etc. then a false match would be anyone who matches all those numbers - 2,6,4,2etc., 2,4,12,2etc. 8,4,12,9etc. 8,6,18,9etc. would all be matches even though there are only 3 segments of any allele, hence 3 suspects. (I understand over 20 numbers the likelihood of match is still incredibly astronomically low)
  #24  
Old 05-22-2020, 02:10 PM
Chronos's Avatar
Chronos is offline
Charter Member
Moderator
 
Join Date: Jan 2000
Location: The Land of Cleves
Posts: 88,635
It depends on how you do the analysis, which means it depends on how much time and money you're willing to throw at the case.
  #25  
Old 05-22-2020, 07:06 PM
Melbourne is offline
Guest
 
Join Date: Nov 2009
Posts: 6,313
Quote:
Originally Posted by Darren Garrison View Post
For anybody reading along at home: It's there at the top of the page referenced: "make millions of copies of a particular section of DNA".

You don't get DNA. You get sections of DNA.
  #26  
Old 05-22-2020, 08:57 PM
Riemann's Avatar
Riemann is offline
Guest
 
Join Date: Nov 2015
Location: Santa Fe, NM, USA
Posts: 8,467
Quote:
Originally Posted by Melbourne View Post
You don't get DNA. You get sections of DNA.
You do get DNA from a PCR reaction.

I think there is some confusion in terminology here. DNA is a material - the polymer that the genome is made from.

I think what you're trying to say is - you don't get the entire genome. If you do PCR, you amplify short segments of the genome. Everything involved - the genome, the PCR primers, the PCR product - is made of the polymer DNA.

Last edited by Riemann; 05-22-2020 at 09:00 PM.
  #27  
Old 05-22-2020, 10:12 PM
Darren Garrison's Avatar
Darren Garrison is offline
Guest
 
Join Date: Oct 2016
Posts: 13,910
Quote:
Originally Posted by Melbourne View Post
For anybody reading along at home: It's there at the top of the page referenced: "make millions of copies of a particular section of DNA".

You don't get DNA. You get sections of DNA.
For anybody reading along at home, Melbourne thinks that making millions of copies of DNA isn't making DNA.
  #28  
Old 05-23-2020, 03:55 PM
Tim@T-Bonham.net is offline
Charter Member
 
Join Date: Mar 2003
Location: Minneapolis, MN
Posts: 15,365
Quote:
Originally Posted by steepone View Post
IANAL but wouldn't the fact that this amateur detective collected and handled the DNA mean it could no longer be used as evidence in any case
Not necessarily.

It would make it more open to challenge by the other side's lawyer:
- did this amateur have appropriate training to process crime scenes?
- did this amateur collect & handle the DNA sample properly, to avoid contamination?
- did this amateur maintain a proper chain of evidence, so that we know the sample sent to the lab is the same one collected at the crime scene?

Police crime-scene technicians have extensive training & experience in this; they have procedures to follow, they have numbered/recorded materials (envelopes, test tubes) to contain the collected samples, an evidence room to hold them until lab tests, etc.

An amateur would not have most of this. All that could be used by the lawyer to raise doubts in the minds of jurors about the accuracy of these specific DNA tests.
  #29  
Old 05-23-2020, 05:13 PM
Riemann's Avatar
Riemann is offline
Guest
 
Join Date: Nov 2015
Location: Santa Fe, NM, USA
Posts: 8,467
Quote:
Originally Posted by steepone View Post
IANAL but wouldn't the fact that this amateur detective collected and handled the DNA mean it could no longer be used as evidence in any case
Quote:
Originally Posted by Tim@T-Bonham.net View Post
Not necessarily...
As OP subsequently explained, steepone had misconstrued the plot. The protagonist is not gathering evidence and doing forensic tests herself, she is amplifying DNA sample to plant evidence (for reasons that presumably become clear in the book).

Quote:
Originally Posted by MorrisCody View Post
The objective of the detective (hey, that rhymes) in the story* is to obtain a sample of the suspect's DNA, amplify the appropriate segments, put the solution into a spray bottle and plant the DNA all over town for the police to find and analyze.

Last edited by Riemann; 05-23-2020 at 05:14 PM.
  #30  
Old 05-24-2020, 01:25 AM
Melbourne is offline
Guest
 
Join Date: Nov 2009
Posts: 6,313
Quote:
Originally Posted by Darren Garrison View Post
For anybody reading along at home, Melbourne thinks that making millions of copies of DNA isn't making DNA.
Deliberate misquoting isn't very nice.
  #31  
Old 05-24-2020, 03:01 AM
Darren Garrison's Avatar
Darren Garrison is offline
Guest
 
Join Date: Oct 2016
Posts: 13,910
Quote:
Originally Posted by Melbourne View Post
Deliberate misquoting isn't very nice.
I in no way whatsoever misquoted you.
  #32  
Old 05-25-2020, 10:01 AM
Nansbread1 is offline
Guest
 
Join Date: Jan 2016
Location: England
Posts: 435
Amplifying the DNA using PCR is one part. You will need, the PCR machine, centrifuges and lab environments with over 100 reagents, can’t go into all of the reagents.

You will need the enzymes that do the reaction. They are quite expensive and need freezers that go to -70 C. The specialist companies may not sell to you.

But what will be the biggest hurdle. 2 things. You will need the DNA or RNA primers and the radio isotopes that label the primers and its constituents. You will not be able to get the license for it.

Last edited by Nansbread1; 05-25-2020 at 10:02 AM.
  #33  
Old 05-25-2020, 10:11 AM
Chronos's Avatar
Chronos is offline
Charter Member
Moderator
 
Join Date: Jan 2000
Location: The Land of Cleves
Posts: 88,635
When I did PCR, we didn't have anywhere near those resources. We had the machine and a small number of reagents (I think only 2 or 3), we didn't need any freezers, and I have no clue what we would even have done with radioisotopes even if we had had them. And all of this fit within the budget of a high school lab.
  #34  
Old 05-25-2020, 10:41 AM
Riemann's Avatar
Riemann is offline
Guest
 
Join Date: Nov 2015
Location: Santa Fe, NM, USA
Posts: 8,467
Quote:
Originally Posted by Nansbread1 View Post
Amplifying the DNA using PCR is one part. You will need, the PCR machine, centrifuges and lab environments with over 100 reagents, can’t go into all of the reagents.

You will need the enzymes that do the reaction. They are quite expensive and need freezers that go to -70 C. The specialist companies may not sell to you.

But what will be the biggest hurdle. 2 things. You will need the DNA or RNA primers and the radio isotopes that label the primers and its constituents. You will not be able to get the license for it.
This is essentially completely wrong, aside from the fact that (as already stated upthread) some basic lab equipment is required.

Radio isotopes are not involved in any of the techniques we have discussed, you do not label primers or use radionucleotides for routine PCR. None of the reagents required for PCR or Whole Genome Amplification are dangerous, and none require a license. PCR and DNA prep/purification requires perhaps 10 reagents, not the 100 that you "can't go into", and standard commercial kits are available (as linked upthread) for Whole Genome Amplification.

Some reagents may last longer in low temperature freezers, but everything required for what we are discussing here is routinely kept in ordinary freezers for months. In fact, the key characteristic of TAq DNA Polymerase, the enzyme used for PCR, is that it is unusually temperature stable. I've never tried it, but I think you could leave it out at room temperature for days and it would retain most of its activity. It's also cheap, as are all the other reagents involved in PCR. You can order custom DNA oligos (primers) for a few dollars, they will arrive in a couple of days via regular mail services.

Last edited by Riemann; 05-25-2020 at 10:45 AM.
  #35  
Old 05-25-2020, 11:19 AM
Nansbread1 is offline
Guest
 
Join Date: Jan 2016
Location: England
Posts: 435
If you are wanting to amplify target DNA you will need the sequence of the sample. How will you get that sequencing done without isotopes. How will you get specific primers to bind to the DNA if you don’t know the sequences.
  #36  
Old 05-25-2020, 12:08 PM
Riemann's Avatar
Riemann is offline
Guest
 
Join Date: Nov 2015
Location: Santa Fe, NM, USA
Posts: 8,467
Quote:
Originally Posted by Nansbread1 View Post
If you are wanting to amplify target DNA you will need the sequence of the sample. How will you get that sequencing done without isotopes. How will you get specific primers to bind to the DNA if you don’t know the sequences.
(1) We're talking about amplifying from human genomic DNA. Obviously the sequence of the human genome is known, so even if we were developing a new protocol we could easily design primers. But if you read the thread, you'll see that we are talking about amplifying the 20 standard CODIS STR loci, which are extensively documented in the literature, along with validated primers and protocols.

(2) Sequencing would require much more specialized equipment; but no sequencing method now in use involves the use of radio isotopes.

Last edited by Riemann; 05-25-2020 at 12:08 PM.
  #37  
Old 05-25-2020, 12:35 PM
Chronos's Avatar
Chronos is offline
Charter Member
Moderator
 
Join Date: Jan 2000
Location: The Land of Cleves
Posts: 88,635
You're amplifying the DNA you put into the machine. Presumably, the amateur has some way of getting a small sample of DNA from the person they're targeting. That's the sample you put in the machine.
  #38  
Old 05-25-2020, 01:17 PM
md2000 is offline
Guest
 
Join Date: Feb 2009
Posts: 15,651
Quote:
Originally Posted by Tim@T-Bonham.net View Post
Not necessarily.

It would make it more open to challenge by the other side's lawyer:
- did this amateur have appropriate training to process crime scenes?
- did this amateur collect & handle the DNA sample properly, to avoid contamination?
- did this amateur maintain a proper chain of evidence, so that we know the sample sent to the lab is the same one collected at the crime scene?

Police crime-scene technicians have extensive training & experience in this; they have procedures to follow, they have numbered/recorded materials (envelopes, test tubes) to contain the collected samples, an evidence room to hold them until lab tests, etc.

An amateur would not have most of this. All that could be used by the lawyer to raise doubts in the minds of jurors about the accuracy of these specific DNA tests.
and the fourth point -

-is the amateur detective an impartial observer in the case?

Presumably, the whole story points to someone who has reason to tilt the investigation in one direction or another. Theoretically(!) police lab techs are impartial observers with no inclination to alter results to favour any particular outcome. Members of the general public, less so. Where they collected a sample, how, and whether they stored it properly are all up for discussion.

Back in the late 1800's a Sherlock Holmes story had someone falsifying fingerprint evidence. planting forensic evidence is not unheard of.
Reply

Bookmarks

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is Off
HTML code is Off

Forum Jump


All times are GMT -5. The time now is 05:55 AM.

Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2020, vBulletin Solutions, Inc.

Send questions for Cecil Adams to: cecil@straightdope.com

Send comments about this website to: webmaster@straightdope.com

Terms of Use / Privacy Policy

Advertise on the Straight Dope!
(Your direct line to thousands of the smartest, hippest people on the planet, plus a few total dipsticks.)

Copyright 2019 STM Reader, LLC.

 
Copyright © 2017