Narrator: This is Science Today. A research geneticist at the University of California, Davis has discovered several genes are responsible for the unpredictable way a female responds to fertility drugs. Dr. Jimmy Spearow says his findings may benefit endangered species.

Spearow: There's a lot of endangered species that are only being held in reserves and zoos and many of these do not adapt well to captive breeding. So if we understood better in terms of the genetic differences in how the reproduction is controlled, we could do a much better job of inducing them to reproduce in captivity, even under less than optimal conditions.

Narrator: Using the same dose of a fertility drug, Spearow found some mice ovulated nine eggs per night while others 54 eggs. The genes linked to these major differences have been mapped and once identified, could be one way of controlling reproduction.

Spearow: More and more species are becoming extinct, so this has applications to understanding how we can improve the reproduction of some of those endangered species because if they don't breed, they're not going to reproduce. We will lose them for sure.

Narrator: For Science Today, I'm Larissa Branin.