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Bulgaria - Summer of Chess
#21
Phil Thomas Wrote:One thing I'm not sure about perhaps you can help?
In the lottery analogy if there are 14,000,000 possible combinations and 140,000,000 lucky dips were sold then typically one would expect around 10 winners.

For DNA tests are all possible combinations equally well populated? This does seem to be a hidden assumption in the stats.

Well, normally during something like a paternity test they might analyse a matter of hundreds of DNA nucleotides, which will almost always be enough to ascertain which one of only a few men are the father. However, it's quite possible that a few other people on the planet have a section of DNA which is the same as this particular person. But if we look at every single nucleotide within a person's DNA then I'm convinced that everyone is totally unique. I mean, even identical twins (such as me and my brother) will not actually have an identical DNA sequence as adults. The reason for this is that mutations spontaneously occur within DNA, often dictated by environmental factors (such as exposure to UV). It's very likely that some of my brother's DNA has mutated in different ways to mine. So in that sense, every DNA combination is equally well populated, as long as your analysis was deep enough to look at the entire genotype of every individual. Currently this would cost a lot of money and take far too long; but it's very likely to be possible in the future - even if dangerously intrusive.

But if we are talking about only small sequences of DNA strands then I would say it would seem to defy natural selection if some weren't more common than others. Some variations of particularly important DNA sequences will be significantly more successful than others, and hence natural selection states that they will be more abundant. This is even still true to a large degree in an advanced civilization like humans. For instance, genetic codes within people that make them more susceptible to certain life-threatenining illnesses are likely to be rarer because the carriers of such codes will likely die sooner/more frequently than others. So if we only scratch the surface then I'd agree that DNA combinations are not equally weighted.

I do think it's interesting to note the similarities between DNA evidence and Chess engine match-up though, as I think it gives a real life example of where statistics are used in court to convict people. If the odds in Ivanov's case are similarly compelling then I see no logical reason why they wouldn't also be treated as conclusively as DNA evidence is, and hence prove Ivanov's guilt beyond any reasonable doubt. Big Grin
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