Gene in Mice Determines Maternal Behavior
Scientists recently discovered a gene, called fosB, that seems to determine whether or not mice will nurture their young. In their experiments, researchers used the "knockout" technique in which strains of mice that lacked the gene were produced. Females of this strain which mated and then had pups did not engage in the normal activities of mothers. They did not gather their pups together, keep them warm, or feed them; rather they ignored the pups. Subsequently, the litters of the mutant mice all died.

In further studies, the pups of the mutant mice were raised successfully by foster mothers which were not genetically altered. However, when mutant foster mothers were placed with the litters, the pups still died. Researchers hypothesize that chemical cues given off by the pups stimulate nerves which activate fosB in the brain of normal mice. FosB is present in humans, but whether or not the gene affects behavior in humans the same it does in mice is undetermined.

Source: "In Tests of Mice, a Gene Seems to Hold Clues to the Nature of Nurturing," New York Times, July 26, 1996