Researchers studying how genes
control animal behavior have had
to deal with many uncertainties.
In
Line
the first place, most behaviors are
(5)
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
(10)
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
(15)
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
(20)
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
(25)
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
(30)
anesthesia.
Since shaking is not
healthy, ethologists do not consider Shaker a behavioral gene.
In con-
trast, ethologists do consider the gene
period (per), which controls the fruit
(35)
fly’s circadian (24-hour) rhythm, a
behavioral gene because files with mutated per genes are healthy; they simply have different rhythms. It can be inferred from the passage that which of the following, if true, would be most likely to influence ethologists’ opinions about whether a particular gene in a species is a behavioral gene? A The gene is found only in that species. B The gene is extremely difficult to identify. C The only effect of mutations in the gene is to make the organism ill. D Neuroscientists consider the gene to be a behavioral gene.
E Geneticists consider the gene to be a behavioral gene.答案选C。有点不能理解，因为21行说不能仅以make the organism ill来判断是否是行为基因，请求解答，谢谢了。 | 
