Chromosome 2 (con)fusion.

Those wacky creationists are at it again. This time, they have a book out that purports to challenge the evidence for human evolution. I haven’t read it, but you can find a thorough review here. From all appearances, it isn’t any better than their previous treatment of junk DNA (reviewed in detail here).

“Creationists publish a terrible book” is not news, of course. It’s not even at the level of “Dog bites man”. More like “Dog poops on lawn”. But what’s interesting is what happened when respected science writer Carl Zimmer asked a very simple question on a creationist Facebook page about a claim made in the book. (It had to be on Facebook, because they don’t allow comments on their website). This time, the argument centers around the origin of human chromosome 2, which biologists have long recognized as resulting from a fusion of two ancestral chromosomes (and which remain separate in modern non-human apes).

You can read all about the drama that ensued on Carl’s blog:

Part One: The Mystery of the Missing Chromosome (With A Special Guest Appearance from Facebook Creationists)

Part Two: The Mystery of the Missing Chromosomes, Continued: An Update From Your Preening Blogger

Part Three: Four Days of Fusion Chromosome Freak-Out

Part Four: And Finally the Hounding Duck Can Rest

True to form, Carl has taken this as an opportunity to write a very informative summary of the research on the evolution of chromosome 2. At this point, we have genome sequences for humans, chimpanzees, and gorillas, and we can pinpoint the fusion site with great accuracy. Some question remains as to exactly when this occurred (it had to be sometime since the divergence of the human and chimpanzee lineages about 6 million years ago), but it’s a slam dunk as far as most biologists are concerned.

In fact, I can hardly believe it’s even an issue at this stage. The creationist book focuses on one aspect of the story, the presence and condition of the former telomeric sequences that are now embedded within chromosome 2. Telomeres are the caps of chromosomes, so finding these sequences within a chromosome provides evidence of past fusion.

But this isn’t the only, or even the main, piece of evidence for fusion. The hypothesis that chromosome 2 is the product of a fusion event has been around for decades, and was initially based on the striking similarity of banding patterns of human chromosome 2 and two separate chromosomes in chimps and gorillas.

Here’s a figure from a review paper published in 1982 (Yunis and Prakash 1982):

The original pattern shown here has been known since 1972 (e.g., de Grouchy et al. 1972). The banding patterns make it pretty obvious that human chromosome 2 lines up with two chimp chromosomes. The telomeric and centromeric sequences found within chromosome 2 are just further confirmation of something that biologists have known about for 40 years.

As it turns out, the authors of the creationist book (predictably) quote-mined a couple of sources, and ignored both the history of the field and more recent data that has emerged since the rise of genome sequence comparisons. As I said, this is not news, but at least we got a Zimmerized review of the subject out of it.

References

De Grouchy, J., C. Turleau, M. Roubin, and M. Klein. 1972. Evolutions caryotypiques de l’homme et du chimpanzé. Etude comparative des topographies de bandes après dénaturation ménagée. Ann. Génétique 15: 79–84.

Yunis, J.J. and O. Prakash. 1982. The origin of man: a chromosomal pictorial legacy. Science 215: 1525-1530.


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