In sequencing, the asymptotic numbers of gaps and contigs have been give the Lander-Waterman model. But the results from the Lander-Waterman model is only asymptotic and doesn't work well when the sequence being sequenced is not long enough (e.g. RNA-seq).
I see no obvious connection between the first paragraph and the following two sentences, except that they refer to a definition of 'coverage'. Is it that what you are looking for. If so, it would help a lot if you can add a sentence stating what you are interested in.
Can you clarify your question? Do you want exact solutions to the problem when the length of the shorter segment is comparable with that of the longer? Do you want to know, for example, what the probability of a given gene having coverage blah when the overall coverage of the transcriptome is blahblah? You could try Leeuwaarden, Lopker and Janssen "Connecting renewal age processes with M/D/1 and M/D/infinity queues through stick breaking"
I see no obvious connection between the first paragraph and the following two sentences, except that they refer to a definition of 'coverage'. Is it that what you are looking for. If so, it would help a lot if you can add a sentence stating what you are interested in.
@Michael I edited it a little so I hope it's more clear now.