From MF So what exactly does 88% match mean?
Posted: Fri Nov 30, 2007 Molly2 Here is a very simplified explanation of how DNA testing works, without any technical jargon 
Lets say you have 20 differently shaped boxes. (These are the 'markers' from your known sample of Madeleine's DNA)
You also have a DNA sample, in which you are trying to find 20 shapes which will perfectly fit (1 in each box).
You can only find 16 shapes in total in your DNA sample (not sixteen that match and lots that don't - just 16 in total.
The 16 that you DO have, match up with a box each - so you have 16 'fits', but no more shapes left.
That is an 80% match - the rest cannot be matched up because there are simply no more shapes left.
If you had 16 shapes that matched, but loads of others left over, then THAT would be someone who has an 80% match to Madeleine - but it could not BE Madeleine, because the left over shapes would show that different 'boxes' would be needed - proving that it is someone else entirely (because Madeleine does not have those 'boxes' in HER DNA).
The reason that is is regarded as 'inconclusive' is that they cannot tell if the remaining 4 'boxes' would be matched up, or not, if they had a larger sample.
Therefore the 80% match does not mean much, until you work out the probability of someone else having an 80% match... it is the probabilities which make the difference. If it is a chance of 1 in 10 then it means nothing... if it is a chance of 1 in a million (and the DNA of the twins or the parents also do not match with the 16 'boxes'), then that is something else entirely. Sadly my scientific knowledge does not run to calculating these probabilities
Mitrochondial DNA could also be used ... this technique is good for very damaged samples and hair that has no root still attached - but it would prove that the hair came from someone in Kate's maternal line (Kate's Grandmother, Kate's Mother, Kate's Aunts and Uncles (on her mother's side), Kate's Cousins (but only those from her Aunts), Kates Cousins' children (but only those from her female cousins), Kate and all 3 of Kate's children.
As we know it is relatively easy to tell if a hair came from a corpse (the core turns blacker and 'bleeds' out into a very recognisable pattern) ... so if they have hair from a corpse that also has mitochondrial DNA that matching Kate, then it would be a logical conclusion that the hair is from Madeleine.... unless Kate's relatives have been dying like flies in the boot of a hire car
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