Gene responsible for making sex deadly

An interesting study published in Nature talks about a deadly gene that makes sex deadly. Ever felt unlucky in love? You’re surely better off than the nematode worm Caenorhabditis elegans. When the Hawaiian and Bristol strains of this worm breed with one another, their grandchildren pay the price: a genetic incompatibility kills a quarter of the embryos. Yet the genes responsible for this brutal outcome seem to be conserved by natural selection. Researchers have found that embryos of C. elegans unlucky enough to be missing one particular gene, called zeel-1, die early in development if their male parent delivered a metaphorical bomb into their embryotic life in the form of a compound produced from an incompatible version of another gene, peel-1, in his sperm. Hannah Seidel and her colleagues at Princeton University in New Jersey, discovered this quirk of nature by accident, when they crossed worms for a different experiment. Discovering that one in four embryos were dying, they suspected genetics might be to blame — patterns of gene inheritance mean that some conditions can affect exactly 25% of offspring. The researchers set to work matching up different worms with each other to see what had happened to the offspring.

C. elegans is almost always hermaphroditic, and almost always reproduces on its lonesome. But occasionally, one of these worms will produce a true male offspring (never a female). This male can then go forth to have sex with another worm. This happens as infrequently as one in a 1,000 generations. The missing zeel-1 , which leaves embryos sensitive to an unknown molecule that stops development, comes from the Hawaiian strain. Meanwhile, the gene for the killer sperm comes from the Bristol strain. So when Bristol males get it together with Hawaiian hermaphrodites, the result can be fatal. Both types of worm are found together all over the world. It is the rarity of sex that probably allows the lethal gene to perpetuate, rather than fading away, says Leonid Kruglyak, who led the study.

The authors suggest that some unknown benefit to the genes involved may counteract the reproductive costs involved in carrying the gene. What that is, though, remains unknown. "It would have to be a big advantage because of the lethality,” says Patrick Phillips, of the University of Oregon in Eugene, who also studies C. elegans evolution.

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