Q25 to Q27:
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.
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Q25:
The passage suggests that neuroscientists would most likely consider Shaker to be which of the following?
Answer: A
why A? What't wrong with E?Thanks!
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