What are the probabilities associated with each level of DNA sample completeness?
Per J35: In the USA, A full dna profile consists of 13 loci (STRs) or 26 alleles, with 15 or more alleles being cause for familial DNA testing.
1. Is there a chart that shows the probability of any random individual matching a certain number of alleles to a given DNA sample?
2. How many alleles are available in most partial DNA samples and what is the normal range and variance of this number in available historic cases? Is it common for a 'partial DNA sample' to include 6 alleles? Would a 2-allele sample even be called a partial or would that just be thrown out?
If we assume the police have an average-sized partial DNA match then maybe we can develop a rough understanding of how significant that kind of DNA evidence would be as a tool for the investigation. If a common partial DNA sample is 6 alleles and this is really only useful for eliminating 40% of the male population, that would be much less significant than the normal layman's conception of the influence of DNA evidence on an investigation.
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Hey bud, haven't read all your post yet but some great questions that I will try and answer to the best of my ability [undergraduate degree - my post grad focused more on molecular side- determining mitogenomes with next gen sequencing and subsequent phylogenetic analysis of species]
A1) probability is dependent on the population frequency data-- you can have a play around with calculators such as this one
http://www.1000genomes.org/announcements/allele-frequency-calculator-1000gb-2014-06-25
A2) You would have a %cut off - say 40% allele match - otherwise you will have many low statistical hits for only a few matching alleles. So yes, 2 or 6 allele match out of 26 alleles = exclusion (see A3).
A3) 6 alleles out of 26 would not be statistically significant: for example the likely hood of two unrelated people sharing the same 6 alleles may be only 1:1250 (example only- depends on the alleles obviously) where as 23/26 alleles is more likely to be in the 1: billion (example only) for the given population.
It should be noted that AUS used ProfilerPlus back in 1997 - looks at only 9 loci or 18 alleles
Hope that helps