The human chromosome 2 is often used as evidence of human evolution. I’ve used it as an example of such for years in my Genetics class. I may need to appeal to those with more knowledge of this topic to answer a few questions, though. (@Swamidass @glipsnort @T_aquaticus come readily to mind) Jeffrey Tomkins at AiG has written (at AiG) pretty extensively on this topic and I wanted to check on a few things. Here is a link to one of his articles:
First, I’ve always taught that the human chromosome 2 arose via Robertsonian translocation (and even said as much in a post here at the BioLogos forum about a month ago). But is this actually true? It seems from the literature that the fusion was an end-to-end fusion and not from a Robertsonian translocation, after all. One of Tomkins biggest objections to the chromosome 2 fusion is that the telomeres are (at least in part) present to prevent end joining, suggesting that this type of fusion should not occur. I know that telomeres also help mitigate the problems with loss of coding information resulting from the 5’ end problem that would arise without the telomere “buffer”. This just has me reconsidering the factual detail I pass on in class.
Second, another of Tomkins’s objections to the fusion hypothesis is the “degenerate” telomere sequence at the fusion point. Am I missing something here? If the fusion did indeed occur in the far-distant past (is there an estimated time of the fusion?) wouldn’t it be perfectly reasonable for the lost-function telomore sequence to have degenerated to the extent that Tomkins describes?
Third, Tomkins notes that sub-telomeric satellite sequences that are prevalent in chimp chromosomes, including 2A and 2B, are absent from human chromosome 2. I don’t have any good reply for this, so any help would be welcome here.
Fourth, Tomkins claims there is no valid evidence for the existence of a cryptic centromere that would have resulted from the fusion. There isn’t as much in the literature as I had expected, at least not from a cursory pubmed search. I did find a couple of independent comments on some bioinformatic work:
Just not a great peer-reviewed article as I would have preferred.
Fifth, Tomkins claims that the proposed fusion site is actually within an intron of the DDX11L2 pseudogene. If I’m understanding his argument correctly, this would indicate that part of the DDX11L2 sequence would have been part of 2A, while the other portion would have been on 2B, which frankly, sounds like a pretty good argument. Any thoughts on this?
Any and all comments appreciated!