What's DNA got to do with it?

Sperm are the ultimate smart missiles. Each contains half the genetic information required to transform a single cell, the egg, into an organism composed of thousands to trillions of cells. Yet, a fertilized egg usually doesn't employ its genes, including the half donated by the sperm, until after a few cell divisions. Does a sperm's DNA have any function before then?

Diane C. Shakes of the College of William and Mary in Williamsburg, Va., answered that question, at least in the worm C. elegans. She and her colleagues identified mutant worms whose sperm precursor cells lacked nuclei and the DNA they would normally contain. Surprisingly, these round cells mature into elongated cells that crawl like normal worm sperm cells. Moreover, when the mutant male worms breed with females, the DNA-bereft sperm still crawl to the oviduct and penetrate egg cells.

Each fertilized egg cell even establishes two distinct halves, along what is called the anterior-posterior axis. Scientists knew that the sperm's point of entry helped determine this axis, but this finding shows that the sperm's DNA plays no role in the process, says Shakes.