Looking at them, you can see the similarities: the nose, the cheekbones, the dimpled chin and long, brown curls.

But what are the chances, right? What are the chances that two California teens would meet online in a roommate hunt, cross the country to attend Louisiana’s Tulane University and learn a semester later they were half-sisters, the daughters of the same Colombian sperm donor?

Emily Nappi, 18, of San Francisco, and Mikayla Stern-Ellis, 19, of San Diego, learned exactly that January 7, when, acting on a suspicion they’d joked about since Father’s Day, the women asked their mothers to hunt down their sperm donor numbers from the Los Angeles-based Calfornia Cryobank. …

“We had so much in common that I decided to e-mail her, Facebook message her and see if we could be roommates,” Stern-Ellis told CNN.