Recombination -- Is Sex Really Necessary?

	http://people.csail.mit.edu/jaffer/GTOL/recombination
	Recombination -- Is Sex Really Necessary?

As important as protein sequence evolution is, a genome needs much larger scale variation to regulate those proteins and to excise and incorporate new genes. Viruses, transposition elements, and recombination provide that variation.

The transfer of genetic material between organisms presents a challenge for the recipient: whether and how to integrate this new material into its genome.

Viruses are one such vector for genetic material. The survival of a potential host species would seem to require that only rarely should transfered genetic material be incorporated.

But what about viruses which don't destroy their hosts? In Are Viruses Alive? ([12]) Villarreal writes:

But viruses called cyanophages enocde their own version of the bacterial photosynthesis enzyme -- and the viral version is much more resistant to UV radiation. If these viruses infect a newly dead cell, the viral photosynthesis enzyme can take over for the host's lost one.

We could consider this arrangement, not as host and parasite, but as a sexual life cycle:

Female gametes (cyanobacteria) live below the surface where ultraviolet radiation is moderate. Thses females replicate by fission.
When female gametes near the surface their chlorophyll is destroyed by the more intense ultraviolet radiation.
The male gamete (cyanophage) fuses with the female gamete, producing a zygote having the gene for ultraviolet-resistant chlorophyll.
The zygote produces capsids which become the male gametes.

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		The Game Theory of Life
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