dna

[jannyneve]

what are the chances of brothers with the same blood group being a close dna match?the reason for my question is that someone close to me has been convicted on dna evidence alone,the brothers all have the same blood group,and we have been told by a scientist that there is no point having them dna tested,and it would be a waste of money,this is our only hope for an appeal,please help.p.s. the person convicted has always maintained their innocence.everything from the age,hair colour,weight,height described in court was completly oppisite to what this person is.thanks.

[jake-the-peg]

DNA matching is not foolproof - At the OJ simpson trial the defense absolutely demolished the DNA evidence. In that case the sample had been mistreated and crucially the sample was small.

Because the sample was small the lab used a technique which basically duplicates the DNA to give a larger sample before it is analysed.

This technique is still used in scientific work but the FBI for one has discontinued it as unreliable in criminal cases.

Having said all that if the sample was of good size and quality and was not mistreated then DNA techniques are easily able to determine between non-identical siblings. Whether or not they have the same blood group.

I don't know what the witness' circumstances are but remember that under pressure people are notorious for seeing something and being absolutely certain that black was white.

[jannyneve]

the dna was 17 years old and was a very small sample,it was tested the same way as in the oj simpson trial,

[jake-the-peg]

What we're talking about here is called PCR (Polymerase chain reaction) which duplicates a small sample into a large one. Unfortunately if the original sample is poor it also amplifies those problems.

After the OJ Simpson case new guidelines were issued in the US.

I believe, but I can't find the reference now that the FBI abandoned prosecutions relying on PCR DNA tests a few years back.

Note the use of the word relying.

Now on one hand you've said that the conviction was solely on DNA evidence but on the other you've said there were witnesses - even if their evidence was questionable.

You may find the the judge did not believe that the DNA evidence was the only basis for conviction. And you must remember that is the US and not the UK.

I would imagine that you would need to show that the standards of evidence governing the use of PCR DNA evidence were not adhered to in order for an appeal to overturn the verdict.

That may be a tall order! You would need to start by seeking the opinion of a forensic scientist specialising in this area who could be cited as an expert witness.

[Peter Pedant]

jannyneve

I think you have posted this a few times - Eddie 51 has given you the best advice - get a solicitor,

dont bother giving us more little details like what a scientist said to your dad's mother in law when theymet in a pub

Get a solicitor

[Azimov]

By all means post an update once you have received legal advice!

I for one would like to hear what the law has to say on the science involved!
I've never trusted the DNA route for forensic evidence personally.

Oh and Good Luck by the way!!