From One Sperm Donor, 150 Siblings One father, tons of kids: Is it a problem? By Kate Seamons, Newser Staff Posted Sep 5, 2011 12:32 PM CDT 21 comments Comments Vials of sperm are frozen seen at a sperm bank. (Getty Images) (Newser) – When Cynthia Daily, her partner, and their son vacation with other families, "it's wild," she says. The kids "all look alike." That's because Daily turned to a sperm donor seven years ago; using the number assigned to her donor, she later searched an online registry for her son's half-siblings, some of whom her family now holidays with. Turns out there are 150 of these kids, and that number is growing. While Daily's son's clan is one of the biggest groups of brothers and sisters to share one donor dad, it's becoming less of an anomaly, reports the New York Times, which says 50-plus-member groups are appearing more frequently in online registries. The concerns are growing in number, too. Some worry of the potential for rare genetic diseases to spread throughout the population. Others fear the real possibility of accidental incest, as unwitting half-brothers and half-sisters often live near the same sperm bank—and each other. “My daughter knows her donor’s number for this very reason,” says the mother of one teen. "She’s had crushes on boys who are donor children. It’s become part of [her] sex education." Critics are clamoring for a legal limit to be imposed on how many kids one donor can father, and some blindsided donors may agree.