They began with an experiment aimed at measuring mutation rates in the minimal cells. They repeatedly transferred a sliver of the growing minimal cell population into petri dishes, which freed the cells to grow without constraining influences like competition. They found that the minimal cell mutated at a rate comparable to that of the engineered M. mycoides<\/em> \u2014 which is the highest of any recorded bacterial mutation rate.<\/p>\n

The mutations in the two organisms were fairly similar, but the researchers noticed that a natural mutational bias was exaggerated in the minimal cell. In the M. mycoides<\/em> cells, a mutation was 30 times more likely to switch an A or a T in the genetic code for a G or a C than the other way around. In the minimal cell, it was 100 times more likely. The probable explanation is that some genes removed during the minimization process normally prevent that mutation.<\/p>\n

In a second series of experiments, rather than bringing over a small group of cells, the researchers transferred dense populations of cells for 300 days and 2,000 generations. That allowed more competition and natural selection to occur, favoring beneficial mutations and the emergence of genetic variants that eventually ended up in all the cells.<\/p>\n<\/div>\n

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