Thread: How reliable is DNA evidence...

I'm probably not the first and I suspect there will be a film out soon on this but just how much weight should be placed on DNA evidence?

As technology improves and DNA testing and techniques becomes more widely available I ask the following questions,

1) How easy will it be to replicate a sample of DNA such that a sufficient quantity could be planted at a crime scene to implicate a third person?


2) Were a prostitute to gain a sample of male DNA could such a sample be used to implicate a third person?

3) Could the theoretical possibility of the above be used as a defence where no other incriminating evidence is available?

We have already seen (in the UK) examples of evidence tampering leading to forensic 'specialists' being denounced.


P.S Happy new year all.

the general take by the judges is that DNA evidence on its own is insufficient, unless it's corroborated by other types of evidence

especially when the samples analysed are miniscule, and the augmentation process may highlight contamination rather than the real evidence

As stated, DNA i suppose is not useful without other evidence,

On the point of framing somone, i suppose if the time was spent (and spent well) it could be done even without DNA. Just one more tool to use

The Guardian has a note on the modern uses of DNA for cold cases. Some interesting stuff there.

They make the valid, but oft-forgot point that DNA is also used a lot for elimination of suspects.

Originally Posted by marnixR

the general take by the judges is that DNA evidence on its own is insufficient, unless it's corroborated by other types of evidence

especially when the samples analysed are miniscule, and the augmentation process may highlight contamination rather than the real evidence

What if the results of a miniscule amount of DNA from blood is corroborated by a morphology exam of hair from exactly the same spot?

How reliable is DNA if the person whose DNA is being tested, has had a blood transfusion from an anonymous donor?

Originally Posted by WVBIG

How reliable is DNA if the person whose DNA is being tested, has had a blood transfusion from an anonymous donor?

Red blood cells contain no nuclei and hence no nuclear DNA.

There is a poor fellow who has served 91/2 years of a life sentence for murder who is due to be released today because new DNA evidence points directly at another suspect. This unfortunate man was convicted on the skimpiest of circumstantial evidence. It seems to be a case where the intelligence and facts were being fixed around the policy. Can’t think where I’ve heard of that before.

DNA may not be a foolproof tool for convicting the guilty, but it’s valuable at least in exonerating the probably-innocent.

http://www.9news.com/news/top-articl...?storyid=84911

Originally Posted by Bunbury

DNA may not be a foolproof tool for convicting the guilty, but it’s valuable at least in exonerating the probably-innocent.

http://www.9news.com/news/top-articl...?storyid=84911

Zigackly. I too made that point earlier, but not as clearly.

I suspect part of the problem is, of course, the lay public's (and hence the average juror's) inability to appreciate statistics and, in particular, Bayes Theorem and its application to test results, which means that sharp lawyers can at the very least, browbeat them into confusion, or more frequently, into being sure of entirely the wrong verdict.

Originally Posted by sunshinewarrio

I too made that point earlier

Greetings from the department of redundancy department.

To add on to what Sunshinewarrio said, the members of the Jury who are chosen, are ideally not meant to be capable of a good deal of reasoning in the case to provide their own conclusion. They are supposed to go with what they believe to be the correct conclusion based on the statements of the lawyers.

Ok. I have another question. How reliable can DNA be when you consider such things as illicit affairs, secret adoptions, & sperm banks?

I think DNA evidence is only as reliable as the scientist/lab processing it.

And as far as setting someone up with it...well, that's silly to me. Criminals aren't that smart.

I can't wait til getting DNA from fingerprints becomes more reliable.

U can always use some one dna n make crimes n the person will be caught not u

Originally Posted by Jeff1244

U can always use some one dna n make crimes n the person will be caught not u

Yeah, I do that all the time.

The real proble with DNA evidence is the partial match, which can, along with other evidence, cause to a false conviction,

I recall reading about a case that some one was convicted and it was the partial DNA match that was the juding piece, About 10 years later it came up that it was the brother of the convicted who did the crime,

This is what i think is the real danger about DNA evidence.

P.S I`m not sure if partial DNA matches are accepted at all to day though.
so this post might be totally useless

Oh exactly, DNA is helpful, but not too much weight should be placed on it, because of course it is not any good without supporting evidence, and convictions should not be decided just on that alone.

In 2006 a sample of what was believed to be possible Bigfoot blood was collected for DNA testing in Canada. The first lab found no DNA at all. A second lab found what it said was a miniscule amount of non-human primate DNA. A third lab found what it said was fungal DNA. With three such different results by three different labs on the same sample, how can DNA testing be considered reliable at all?

Lets go for another long post...

Originally Posted by Anonymous

1) How easy will it be to replicate a sample of DNA such that a sufficient quantity could be planted at a crime scene to implicate a third person?

2) Were a prostitute to gain a sample of male DNA could such a sample be used to implicate a third person?

3) Could the theoretical possibility of the above be used as a defence where no other incriminating evidence is available?

1) I was surprised at how easy this is to do. Like scarily easy. I actually tested this in college.

2) You need to clear this one up for me. Is the third person the male that the prostitute got the DNA from or another person entirely? If the former, then yes, but the storage and transport of the DNA sample would prove difficult if we're talking semen (Possible, Improbable). If the latter then no. Plain and simple (Except in the case of identical twins).

3) No, because as already stated, Numerous pieces of evidence are needed.

Next...

Originally Posted by WVBIG

How reliable is DNA if the person whose DNA is being tested, has had a blood transfusion from an anonymous donor?

Very reliable, As there are usually no whight blood cells in the donor blood and even in the event of a straight person-to-person transfusion, unless the test is taken straight away, the body will destroy the WBC due to their different DNA (Seen as an attacking body), and simply creates more in the bone marrow.

A question that I would like to ask is 'If there is a bone marrow transplant, does this effect the DNA of WBCs?'

Originally Posted by WVBIG

Ok. I have another question. How reliable can DNA be when you consider such things as illicit affairs, secret adoptions, & sperm banks?

DNA can tell you if two people are your parents, sure, but you'd have to find them to get the DNA test. I don't see that lineage matters. There is controversey over 'evil genes' and 'psychopath' genes, etc... but up to date there is no concrete evidence supporting a physical link to behaviour.

Originally Posted by Pikkhaud

The real proble with DNA evidence is the partial match, which can, along with other evidence, cause to a false conviction,

I recall reading about a case that some one was convicted and it was the partial DNA match that was the juding piece, About 10 years later it came up that it was the brother of the convicted who did the crime,

This is what i think is the real danger about DNA evidence.

P.S I`m not sure if partial DNA matches are accepted at all to day though.
so this post might be totally useless

The partial match is a wonderful result. It tells you that you're close to matching the DNA to someone and that it is likely to be someone from this person's family. It also tells you that the person who yeilded a partial match is innocent. At the time though (looking at that '10 years later...' line) I would think that DNA was still in it's early stages hence the mistake.

Fun fact: DNA is unique, but the tests only measure the most likely variant area. There is in fact a one in a billion chance of a match with someone else using the area that is profiled, but take solace that these matches can be ruled out by profiling other areas of the DNA strands. As there have been snowflakes that are identical, down to a molecular level (how cool is that?) you can take solace in the fact that there will never be anyone quite like you, unless you're an identical twin.

Originally Posted by sunshinewarrior

The Guardian has a note on the modern uses of DNA for cold cases. Some interesting stuff there.

They make the valid, but oft-forgot point that DNA is also used a lot for elimination of suspects.

Question: How much of a partial profile do you need to point to ethnicity or
a population group? (say Scandinavian vs African). Is this an issue of nuclear
dna or mtdna, or both?

Any help appreciated -