DNA testing makes them easy to trace.

Some sperm banks are changing their policies for fear that anonymous donors might withdraw from the program and hurt their bottom line. Cryos International, a sperm bank based in Copenhagen, Denmark, that claims to be the largest bank in the world, has started to offer a new program that it's dubbing "Invisible Donors." It's a system where donors can offer very few registered characteristics so they will be more difficult to track, and the bank keeps track of them by fingerprints instead of donor number.

"I'm fully aware of the future child's needs, and I fully understand and support children who will search for their donor [and] half-siblings, but the fact is that it is wrong to search for a donor who claimed anonymity," says Ole Schou, the director of Cryos International.

She may be right that it will become increasingly difficult for a donor to hide, which means the moral decision of whether to trace him and ignore his request for anonymity will rest less on the banks and more on the parents and offspring. If DNA testing does become more ubiquitous, it may be that even a very few traits will make the men traceable. What will they do then? wonders Kramer. "Create men without DNA?"Become a fan of DoubleX on Facebook. Follow us on Twitter.

Correction, March 1, 2010: The article originally said Michelle Jorgensen lived in Nederland, Colo. She lives in Sacramento, Calif. ( Return to the corrected sentence.)

Correction, March 2, 2010: This article originally implied that mothers pass their mitochondrial DNA only to daughters. They pass it to both children. (Return to the corrected sentence.)

Correction, March 3, 2010: The article stated that Alice Ruby spearheaded the idea of identity-release donors. It was the Sperm Bank of California that spearheaded the idea in 1983. Ruby joined the bank in 2002. Also, the article stated that most families are not interested in finding their donors. Bank research shows that 80 percent of donor conceived children are interested in finding donors, although only 30 percent of families have come looking for them. (Return  to the corrected paragraph.)