New genes evolved in the lab at super-high speed

In their study, which is now being published by Science, the researchers have experimentally tested a specific model (presented in PNAS 2007) which explains how new genes develop. The model states that a gene to begin with can have a weak, secondary activity apart from its strong, main activity. If this secondary activity becomes important, for instance if the organism’s environment changes, the number of copies of the gene in the population can increase very quickly.

One example of environmental change could be that the organism is exposed to a poisonous substance (e.g. antibiotics, herbicides, insecticides) which it must tackle in some way to survive. The increasing number of gene copies also increases the probability of mutations being selected, leading to the secondary function being improved. When these mutations have appeared the extra copies can disappear leaving two genes, one original with its normal function and one copy with an improved secondary function.

The model was tested in the laboratory by researcher Joakim Näsvall by selecting for a bifunctional gene involved in the synthesis of two amino acids, tryptophan and histidine. Bacteria with this gene were then cultivated on growth substrate lacking both amino acids, which led to the selection for gene amplification resulting in up to 20 copies of the same gene. Later mutations caused different gene copies to become better at either tryptophan or histidine synthesis, or in some cases both reactions.

‘Joakim Näsvall’s convincing experimental results provide strong support for our suggested model. They show how new genes can develop after only a few thousand generations of bacterial growth in the laboratory, corresponding to about a year in real-time, if the right selective pressure is present’, says professor Dan Andersson, responsible for the study.

The research has been funded by the Swedish Research Council.