Students in a biology class investigated why individual house mice (Mus musculus) can differ from one another in their responsiveness to potential rewards. The students compared wild-type mice and knockout mice, which are mice with specific genes deactivated, when mice of each type were presented with the same reward system for particular behaviors. Finding that knockout mice with the gene Cartpt deactivated tended to show less sensitivity to rewards than did wild-type mice, the students concluded that differences in reward responsiveness among house mice in nature are solely attributable to variations in the level of expression of Cartpt.
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Verbal·Information and Ideas·Command of Evidence
hardWhich finding, if true, would most directly weaken the students’ conclusion?
A
The mice with Cartpt deactivated were identical to the wild-type mice except with regard to reward responsiveness.
B
The level of expression of Cartpt does not appear to affect the functioning of any other genes in house mice.
C
A sampling of house mice captured in natural settings shows that individual mice can differ from one another in the level of expression of Cartpt.
D
Some wild-type mice were very similar to the knockout mice with regard to reward responsiveness but showed a wide variety of levels of expression of Cartpt.