There likely are several species of killer whales.

• Position: Genetic Sequencing

Strong genetic evidence supports the theory that there are several species of killer whales (Orcinus orca, also known as orcas) throughout the world's oceans, reports the National Atmospheric and Oceanic Administration. Scientists have suspected that fact for some time because of differences in behavior, feeding preferences, and subtle physical features. Yet, until now, DNA analysis has been inconclusive due to the inability to map the entire genetic picture, or genome, of the whales' mitochondria, an organelle within the cell inherited from the mother.

"The genetic makeup of mitochondria in killer whales, like other cetaceans, changes very little over time, which makes it difficult to detect any differentiation in recently evolved species without looking at the entire genome," explains Phillip Morin, lead author and geneticist at NOAA's Southwest Fisheries Science Canter, La Jolla, Calif., "but by using a relatively new method called 'highly parallel sequencing' to map the entire genome of the cell's mitochondria from a worldwide sample of killer whales, we were able to see clear differences among the species."

In all, tissue samples from 139 killer whales were analyzed. Samples came from those found in the North Pacific, North Atlantic, and oceans surrounding...