DNA evidence: Fact of Fiction...?

[Stormtropper]

Experts will only tell you enough to support their hypothesis.

...my dad is a bio-chemist whos doing some research about the correlation between a particular enzyme receptor and cancer or something like that...

...just recently, I believe he wrote a review about a study someone did about how they prevented cancer by giving patients (or were they lab rats...I dont' know...not an expert) a certain inhibitor...but they convienately left out the fact that the vast majority of their patients died of hear disease before they had a chance to develope the cancer...

It is safe to say that a percentage of data presented by experts will be misleading, and it is always wise to do your own independent research to get the full view of things.

[Saitek]

Hi Paul, to answer your question from what I know the facts are that it is not infallible.
Real nature of course has clones of DNA all the time. Identical twins have the same DNA for example. So already you have a rather unusual but obvious example.

However, the experts cannot say that even a single born child is free from possesing the same DNA as others. The facts are it is so remotely unlikely that as yet no cases have been found, but it is however mathmatically possible.

Also, perhaps more importantly, small amounts of DNA can be difficult to work with and contamination as well as accidental smears can be left anywhere. For example how do you argue that a person has held something if the weapon or item has been open to the air?

It is also worth remembering that our judicial system and police force are corrupt and is partly why people get handed down sentences that later turn out to be totally unfair.

Basically I believe DNA evidence is reliable, but it also has to be reasonable. Take this fake case:
If I dropped in to see X for a visit during which we had an argument which the neighbours heard. I used the breadknife in the kitchen to chop an apple and I left it out on the worktop. I also did some ironing for X and left it out. Later M comes in through an unlocked door. M is fully clothed from head to toe and puts on some of X clothes that I ironed to mask himself yet further. He then takes the knife and fatally kills X as he walks out of the bathroom. M leaves without a trace. In that scenario the DNA is true and I am obviously the killer.

Usually criminals are idiots, but there are always exceptions and there are unsafe convictions in UK jails and in other countries too which have used DNA as evidence.

[Hagar]

It is safe to say that a percentage of data presented by experts will be misleading, and it is always wise to do your own independent research to get the full view of things.

The problem with that is that the judge & jury will invariably believe the prosecution's expert witnesses. This is not an isolated case & explains my cynicism. http://news.bbc.co.uk/1/hi/health/4114688.stm

[Saitek]

Yep nothing wrong with the data Doug - just the people using it.  :-[

[Stormtropper]

However, the experts cannot say that even a single born child is free from possesing the same DNA as others. The facts are it is so remotely unlikely that as yet no cases have been found, but it is however mathmatically possible.

Yes it is mathmatically possible...

...but take this into consideration, a human has more than 30,000 genes.

...and for anyone one who has recently taken biology or genetics, there is a dominate and a recessive allele for nearly every gene. (This is not taken into consideration of co-dominates and incomplete dominates or anything like that; for example, eye color and height are controlled by an upwards of 20 or 30 alleles...but we'll just do 2 per gene to keep it simple...)...

...so basically, that comes out to be 230,000 unique combinations...

...which equals...

...hey, wudda ya know, neither my TI-92+ nor my TI-89 Titanium (2 of the most powerful personal calculators, can come up with a solution for that one...

...and just simply marks it as infinity!

[Stormtropper]

The problem with that is that the judge & jury will invariably believe the prosecution's expert witnesses. This is not an isolated case & explains my cynicism.

Well, if the court's intent really is to find the truth and serve justice, the defense will call their own expert and give the other half of the story

...and if it isn't, you're screwed even before they brings in the expert, so you have nothing to fear. Your fate has already been sealed.

[beefhole]

The problem here is that we seem to be striving for a perfect justice system, which is, of course, foolish.

Innocent people will always go to jail.  For as long as capital punishment exists, we will always send innocent people to be executed.  The system is as human and flawed as those who run it, and therefore we can only hope to minimize these mistakes, not erradicate them.  The modern system (last ten years or so when proper procedures have been set up) of DNA evidence has greatly, greatly decreased the number of errors made.  I'll try to find the study that shows this, I read it a year or so ago and have since misplaced it.

And yeah Doug, you're going to have the rogue miscalculating experts.  People are going to be wrong sometimes.  What about the 99.9% of the time that they're right?  To me, it's like refusing to ever fly again because of the crash in Brazil, or refusing to go to school because of a recent shooting.  As I said in the previous paragraph, it's going to happen, and there's nothing that can be done about it without getting rid of ALL experts, which would, to say the least, not be wise.  

I again assert that these isolated cases are not a blanket reason to be cynical about ALL experts, again pointing you to the example of my dad.

And to answer your question Fozz, it's fact, the vast majority of the time.  If you are a victim of said scenario, well, that's just bad luck.  It doesn't mean we should do away with DNA evidence.

edit: I really don't mean to say I'm any more right than you are Doug, just presenting my side.  Sorry if it came off preachy/elitist.  Knowing you, I have no doubt you have your reasons.  Being the son of two very logical scientists, I'm bound to react this way

[Hagar]

[quote]And yeah Doug, you're going to have the rogue miscalculating experts.

[beefhole]

You know I respect your opinions. I'm sure your Dad is highly qualified but I'm afraid that far too many of these so-called "experts" have later turned out to be complete frauds or incompetents for me to change my opinion of the breed. I'm speaking of the UK where, fortunately for their victims, capital punishment was abolished in 1965 for all crimes except treason and piracy & completely abolished in 1998. As I mentioned earlier, disgraced Professor Sir Roy Meadow is just one example of a flawed "expert".

I understand your experience with experts is, apparently, very different than mine.  In terms of life experience, I'm kinda sorta lagging behind you ( ), so I respect a viewpoint shaped from personal experience.

Please note that I don't wish to change the subject onto capital punishment.

Nor do I.  I actually had a disclaimer attached and then decided that would've been too wordy a post.

[beefhole]

Experts will only tell you enough to support their hypothesis.

...my dad is a bio-chemist whos doing some research about the correlation between a particular enzyme receptor and cancer or something like that...

...just recently, I believe he wrote a review about a study someone did about how they prevented cancer by giving patients (or were they lab rats...I dont' know...not an expert) a certain inhibitor...but they convienately left out the fact that the vast majority of their patients died of hear disease before they had a chance to develope the cancer...

Don't mean to butt heads again, but I'd just like to say you're again using an isolated example and drawing broad conclusions from it.  This in no way supports the statement that "experts will only give you enough info to support their hypothesis," a statement I believe to be untrue.

It is safe to say that a percentage of data presented by experts will be misleading, and it is always wise to do your own independent research to get the full view of things.

That much is 100% correct.

[Hagar]

[quote]I understand your experience with experts is, apparently, very different than mine.

[Stormtropper]

Don't mean to butt heads again, but I'd just like to say you're again using an isolated example and drawing broad conclusions from it.  This in no way supports the statement that "experts will only give you enough info to support their hypothesis," a statement I believe to be untrue.

It's usually much less severe than that, but ambigious and incomplete data are presented all the time. From my personal experiences (most of which is just watching my parents work), about 1 out of 10 "experts" seems kinda shady. They're experts because they're understand complictated concepts and ideas, they got there either by 1. being very talented and hard working or 2. knowing what you need to know to think that he is always right.

[beefhole]

It's usually much less severe than that, but ambigious and incomplete data are presented all the time. From my personal experiences (most of which is just watching my parents work), about 1 out of 10 "experts" seems kinda shady. They're experts because they're understand complictated concepts and ideas, they got there either by 1. being very talented and hard working or 2. knowing what you need to know to think that he is always right.

Yup, that's true again.  In the post I quoted you were (possibly unintenially) speaking about ALL experts.

[Stormtropper]

Yup, that's true again.  In the post I quoted you were (possibly unintenially) speaking about ALL experts.

...or you can unconditionally believe "experts" and perceive them as some sort of minor deity

[beefhole]

...or you can unconditionally believe "experts" and perceive them as some sort of minor deity

Sorry.  More confusion.  I mean the FIRST time I quoted you.

Experts will only tell you enough to support their hypothesis.

...my dad is a bio-chemist whos doing some research about the correlation between a particular enzyme receptor and cancer or something like that...

...just recently, I believe he wrote a review about a study someone did about how they prevented cancer by giving patients (or were they lab rats...I dont' know...not an expert) a certain inhibitor...but they convienately left out the fact that the vast majority of their patients died of hear disease before they had a chance to develope the cancer...

Right there.  Please take note we've been on the same page for everything else