quote: I am a bit surprised because I did assume that the number of chromosomes would be the major indicator, which I also assumed wouldn’t be hard to determine, but you didn’t address that part of the question. (“What are the defining factors: the number of chromosomes only?” )
No, it is quire possible for different species - even those that are not closely related - to have the same number of chromosomes. Chimpanzees, orangutans, gorillas and hares all have 24 pairs of chromosomes. Humans and Reeves's muntjacs have 23 pairs of chromosomes.
I'm pretty sure that Crashfrog is wrong, because if it worked that way an indel IN the intron would affect the gene, so overall the risk of frameshift mutations would go up. The statistics don't work out in a way that favours his view, either.
If, on the other hand introns reset the reading frame, then the effect of indels would be limited to the start of the next intron - assuming that the frameshift doesn't mess that up. I'm speculating here, but it sounds like something that might be true....
quote: Look, you guys can be as skeptical as you like, but this is straight out of Leninger Principles of Biochemistry, Inferring Phylogenies, and for that matter Wikipedia:
Crash, that quote doesn't say anything about the non-coding regions being an advantage because they might get extra mutations putting things right. That idea is still very implausible just from statistical principles.
The question I'm really interested in is how this protection works, and your quote doesn't address that at all.