Mutagenèse et adaptation
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One of the tenets of the neodarwi- nian paradigm is the separation bet- ween selective pressure anf genera- tion of variability. Recent work on "directed" or "adaptive" mutage- nesis has challenged this view. The debate moved from the possibility of producing only useful mutations to the possible link betw<een envi- ronment and control of genetic variability. Taking into account the behaviour of parasitic DNA (plasmid, transposable element or phage) when the survival of their host is threatened by stress could shed a different light on some of the adap- tive mutagenesis data. Incidentally, mutagenesis observed under non- lethal selective pressure shows that although the environment is not able to direct mutations it can in- crease their frequency even in the absence of exogenous source of DNA lesions. After discussing re- sults supporting these views we will discuss the adaptive role of such an increased mutagenesis in response to strong selective pressure, under- lying its possible implications for cells submitted to strong selective pressure (i.e. tumour cells or bacte- rial pathogens).