Much of the genome of "Rattus norvegicus" has been sequenced. McClintock also conducted a 1978 study of estrous synchrony in Norway rats ("Rattus norvegicus"). Homo sapiens, Rn for Rattus norvegicus, Mm for Mus musculus, or Dn for Danio rerio. "M. travassosi" was found infesting the Brown rat ("Rattus norvegicus") in Brazil. It is not found in humans, but only in "Rattus norvegicus". One of the more common rodent models is the Norway rat ("Rattus norvegicus"). The Norway rat ("Rattus norvegicus") also utilizes social learning behaviors to find food sources. In 2004, researchers conditioned rats ("Rattus norvegicus") to fear a certain stimulus, through electric shock. When modern biologists refer to "rats", they almost always mean "Rattus norvegicus". "Rattus norvegicus domestica" which is bred and kept for scientific research. "G. neoplasticum" is a gastrointestinal parasite of rats, "Rattus norvegicus" and "R. rattus".