The Strange Tale of a New Species of Lizard

In the 1960s, scientists noticed that some whiptail lizard species had a strange genetic makeup. They have two copies of each chromosome, just as we do, but each copy is very different from its counterpart. The genes look as if they come from different species. Perhaps stranger, many species produce no males. The eggs of the females hatch healthy female clones, a process known as parthenogenesis. Normally, unfertilized animal eggs have only one set of chromosomes. The second set is derived from a male’s sperm following fertilization. But parthenogenic female whiptail lizards can duplicate the chromosomes in their offspring without males. These findings led scientists to a hypothesis for how these strange species came about: Sometimes individuals from two different species of whiptail lizards interbreed, and their hybrid offspring carry two different sets of chromosomes.