Researchers studying how genes control animal behavior have had to deal with many uncertainties. Inthe first place, most behaviors are governed by more than one gene, and until recently geneticists had no method for identifying the multiple genes involved. In addition, even when a single gene is found to control a behavior, researchers in different fields do not necessarily agree that it is a "behavioral gene." Neuroscientists, whose interest in genetic research is to understand the nervous system (which generates behavior), define the term broadly. But ethologists—specialists in animal behavior—are interested in evolution, so they define the term narrowly. They insist that mutations in a behavioral gene must alter a specific normal behavior and not merely make the organism ill, so that the genetically induced behavioral change will provide variation that natural selection can act upon, possibly leading to the evolution of a new species. For example, in the fruit fly, researchers have identified the gene Shaker, mutations in which cause flies to shake violently under anesthesia. Since shaking is not healthy, ethologists do not consider Shaker a behavioral gene. In contrast, ethologists do consider the gene period (per), which controls the fruit fly's circadian (24-hour) rhythm, a behavioral gene because files with mutated per genes are healthy; they simply have different rhythms.


The passage suggests that neuroscientists would most likely consider Shaker to be which of the following?


An example of a behavioral gene

One of multiple genes that control a single behavior

A gene that, when mutated, causes an alteration in a specific normal behavior without making the organism ill

A gene of interest to ethologists but of no interest to neuroscientists

A poor source of information about the nervous system

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