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Practice_3.docx-Practice 3 The following questions refer
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Practice 3
The following questions refer to Figure 27.1 below, which is the same as Figure 27.10 in the
In this 8-year experiment, 12 populations of
E. coli
, each begun from a single cell, were grown in
low-glucose conditions for 20,000 generations. Each culture was introduced to fresh growth
medium every 24 hours. Occasionally, samples were removed from the populations, and their

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fitness in low-glucose conditions was tested against that of members sampled from the ancestral
(common ancestor)
E. coli
Figure 27.1
Which term best describes what has occurred among the experimental populations of cells
over this 8-year period?
A) microevolution
B) speciation
C) adaptive radiation
D) sexual selection
stabilizing selection
Answer: A
If it occurs in the absence of any other type of adaptation listed here, which of these is least
reasonable in terms of promoting bacterial survival over evolutionary time in a low-glucose
A) increased efficiency at transporting glucose into the cell from the environment
B) increased ability to survive on simple sugars, other than glucose
C) increased ability to synthesize glucose from amino acid precursors
D) increased reliance on glycolytic enzymes
increased sensitivity to, and ability to move toward, whatever glucose is present in its habitat
Answer: D
Which of these can be inferred from Figure 27.1?
A) Most of the genetic change that permitted adaptation to the new, low-glucose environment
occurred toward the conclusion of the experiment.
B) Rates of mitosis increased over the course of the experiment.
C) The highest rate of genetic change occurred during the first quarter of the experiment.
D) After 5,000 generations, the bacteria were 100% more fit than the original, ancestral bacteria.
Answer: C

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If the vertical axis of Figure 27.1 refers to "Darwinian fitness," then which of these is the
most valid and accurate measure of fitness?
A) number of daughter cells produced per mother cell per generation
B) amount of ATP generated per cell per unit time
C) average swimming speed of cells through the growth medium
D) amount of glucose synthesized per unit time
number of generations per unit time
Answer: E
If new genetic variation in the experimental populations arose solely by spontaneous
mutations, then the most effective process for subsequently increasing the prevalence of
the beneficial mutations in the population over the course of generations is
A) transduction.
B) binary fission.
C) conjugation.
D) transformation.
E) meiosis.
Answer: B

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