I make no presupposition regarding the length of the genome. Read what I said again. Go to any point within the entire genome, you have a 25% chance of finding any particular nucleotide base. Pluck any string of 19 out of the genome; regardless of how long the entire genome is, this is the chance that it will match this sequence. That is the calculation I did. True, if there are multiple sets to choose from, that increases the odds of finding this sequence, but that isn't the calculation I did. I gave the chance that any single set of 19 matches. I never tried to represent it as anything else.
I make no presupposition regarding the length of the genome. Read what I said again. Go to any point within the entire genome, you have a 25% chance of finding any particular nucleotide base. Pluck any string of 19 out of the genome; regardless of how long the entire genome is, this is the chance that it will match this sequence. That is the calculation I did. True, if there are multiple sets to choose from, that increases the odds of finding this sequence, but that isn't the calculation I did. I gave the chance that any single set of 19 matches. I never tried to represent it as anything else.