TT GWD9-25

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?

1. An example of a behavioral gene
2. One of multiple genes that control a single behavior
3. A gene that, when mutated, causes an alteration in a specific normal behavior without making the organism ill
4. A gene of interest to ethologists but of no interest to neuroscientists
5. A poor source of information about the nervous system

Answer: A

why A? What't wrong with E?Thanks!