The Incredible Shrinking Genome

Shipud writes "Mammalian genomes have been shrinking for about 65 million years, roughly since the dinosaur extinction. Why? And why were ancient mammalian genomes three times larger than they are today? A new article in Genome Biology and Evolution tries to explain this bizarre finding, and why the genomes of mammals (but not of other living groups) are still shrinking. 'Once [the dinosaurs] were gone, mammals started to radiate, fill those niches, and a whole new level of competition arose. The selective advantage of not having a genome encumbered by potentially damaging mobile DNA elements has probably become critical at this "be ye fruitful and multiply; bring forth abundantly in the earth, and multiply therein" stage. In effect, the genomes of mammals has been shrinking by removing mobile DNA elements, just after the KT boundary. And according to the model presented in this study, this process is still ongoing: mammalian genomes are not at an equilibrium size. Unlike flies, mammals are still cleaning up.'"

Comments

Re:smaller code size without copy& paste

[lavaforge]

Are we seeing the same tendency in other warm blooded creatures, such as birds?

Re:entropy is winning

[tomhudson]

On the other hand, a shorter DNA strand has less room for errors that might be non-life threatening.

Meaning duplication errors are magnified.

... but since those duplication errors ARE life-threatening, they get removed from the gene pool more efficiently. So over time, the shorter genes would tend to have better duplication, since the ones that don't duplicate properly are culled much more ruthlessly (ok - "ruthlessly" is an anthropomorphism - but you know what I mean).

So then we have the competition being between longer gene strands that aren't as efficient in duplicating, allowing more errors, and shorter genes that are better at making near-perfect copies of themselves. The shorter ones would tend to dominate - sort of like an evolutionary "principle of parsimony" - the shortest gene sequence that gets the job done wins.

Because our environment is stable

[naasking]

The genome is shrinking because there is a selective advantage to a smaller genome when the environment is stable. Fewer errors can occur when copying for example. In unstable environments, having a larger genome with more adaptive mutations is a selective advantage. Shorter genomes marks species that are highly specialized to their environment.

Re:Not quite.

[BrokenHalo]

The question is, can you attribute any intelligence on the part of the viruses as contributing to this process?

No. I was merely postulating that their chemistry is way beyond cool, and that if I were a God, I would be fucking proud to have come up with them. :-)