Biology Now, 2e

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42.2 ̊C

37 ̊C

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Scientists grow 115 separate, genetically

identical populations of E. coli at a

comfortable temperature of 37 °C, or 98.6°F.

The populations reproduce through 2,000

generations while being subjected to an

increased heat of 42.2°C, or 107.96°F.

One sample is taken from each of the 115

populations, and the genome is sequenced.

The research continues. The next step is to

figure out how the mutations in the RNA

polymerase complex and in rho helped the

E. coli survive the heat.

1,25 8 molecular changes, averaging 11

genetic mutations per clone, are detected.

To help survive the heat, the E. coli tend

to mutate along two different trajectories:

• Mutations in the RNA polymerase complex,
  an enzyme that transcribes RNA.


• Mutations in the rho gene, which encodes
  a protein that stops RNA transcription.

In the laboratory, scientists can manipulate populations

of organisms to watch evolution in real time via artificial

selection. In 2012, researchers at UC Irvine manipulated

the growing environment of Escherichia coli bacteria,

exposing them to far hotter temperatures than normal,

to see if they would adapt. Most of the bacteria adapted

via one of just two primary pathways.

Watching Evolution

Happen