I refrain from discussing this anymore as it is obvious that nobody is interested in facts that disprove their narrative.
Yes, it is possible to get a significance of "1 in a billion" with 7/15 markers. The number of markers matters mostly when you have very little, like 1-2 (maybe even 3-4). However, once you have sufficient number of markers the main determinant of significance or probability are the actual alleles (those numbers in the profile).
These calculations have nothing to do with forensics and is a commonly thought topic in any Genetics class (Population Genetics). It is called the Hardy-Weinberg equilibrium.
is the correct chance that the sample matching to TH's mother with 7/15 markers 1 in a billion people?
"1 in a billion unrelated people", FTFY.
You need the FBI frequency database from 2005 that she used to see if she calculated correctly.
If not what is the real number?
These are extrapolations on the population statistic on relatively small samplings. There are simple ways to check how off you expect to be. They even do those checks but for some reason they are not required to report them in the courtroom, which I believe they should.
The main point though is that it is possible to get that significance which some people are claiming it is not. Also, some claims on how much off that number is, like yours above, would mean that 95% of Wisconsin are identical twins.
There are other issues at hand here:
Should they use profiles from such damaged samples to calculate these statistics?
Is SC allowed to claim a statistic at the same time she is not allowed to say it is a full match?
To me the most interesting question is, what did the graph (raw data) on which that DNA profile is based on look like?
Should the frequency tables be made public and should they report all their checks on how off the Hardy-Weinberg probabilities are? (there are assumptions made when this is calculated that are violated in reality, so they always need to do checks to see how much it is off)
These are things I would be asking. People have been barking at the wrong tree with this "7/15 cannot be 1 in a billion" and unless they are going to revolutionize the field of Population Genetics, without even taking one course on the topic, I would not take it too seriously.