Marcy Darnovsky is the associate executive director of Oakland's Center for Genetics and Society, so she's used to hearing weird tales from the cutting edge of genetics: rabbits that glow in the dark, or people seeking genes for immortality. Nevertheless, she was flummoxed when she picked up The New York Times and found an ad asking: "Do you want to choose the gender of your next baby?"

Sujatha Jesudason, her colleague, was equally surprised when a similar ad appeared on Hotmail. Soon, the pair began noticing what seemed like a sex-selection advertising blitz -- the come-ons were everywhere, from in-flight magazines to publications catering to the Bay Area's Indian community.

The ability of ordinary couples to choose the sex of their offspring is no longer science fiction, thanks largely to MicroSort, a division of the Virginia-based Genetics and IVF Institute and the name of its trademarked sperm-sorting technique, which offers a strong likelihood of selecting one sex over the other. Although still in clinical trials, the availability of gender selection for the masses has begun to permeate popular consciousness via...