Tracing and quantifying inheritance over many generations Apologies if this is the wrong location for this question, and please feel free to point me in the right direction with appropriate Anglo-Saxon embellishments...
I'm after some ball-park numbers for the following questions (plus any hints how to calculate them for different params - e.g. less generations, larger starting pop.):
Given a starting population of 10,000, and given 2,500 generations, with an end population of 5,000,000,000

What are the chances of being a direct descendant of 1 individual of the original 10,000?
If you had a DNA sample of that individual, would you be able to tell if you were a direct descendant?
Would siblings of the original individual confuse things with regard to Q2?
Since it seems my comment helped, I've been suggested to post this as an answer...
I'd reccomend everyone interested in these sort of population genetics to have a look at 'The Ancestors Tale' by Richard Dawkins. In particular, chapter 0, which deals with human/hominid genetics. That should help answer questions. The relevant part of the book appears to be available online for free in GoogleBooks (https://books.google.co.uk/books/about/The_Ancestor_s_Tale.html?id=s86_CQAAQBAJ).
Below I'll note down the answers from the comments section, not because I wrote them but I figured it might help anyone who stumbled over this question afterwards:

The chances of being a direct descendant of 1 individual of the original 10,000 is 100%, assuming they have any descendants. - Tom Melly

If one had a DNA sample of that individual, one could use uniparental markers (either Y chromosome for men, or mtDNA for women) to infer whether they are a direct descendant. - 4galaxy7


(My guess is that it doesn't have to be uniparental markers. Other genes might work just as well. I'm thinking of Neanderthal/Denisovan work. But I might be wrong.)