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2013-05ClawF1.jpgClick to Enlarge ImageAlthough they serve the same function across the plant, animal and fungal kingdoms, sperm and eggs vary wildly in their structure and biochemistry, even among closely related species. How did such divergent structures evolve, from the hooked, fast-swimming rodent sperm clumps to the two-inch–long fruit fly sperm? Many genes that determine sperm and egg structure and biochemistry are rapidly evolving, constantly changing the chemical environment necessary for the sperm to bind to the egg. These genes can be some of the most rapidly evolving in the genome, at times outstripping the evolutionary rate of genes involved in immune responses. Claw describes evolutionary contexts  from model systems (abalone, fruit flies and primates) that can give rise to rapid evolution in gametes.

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