Discontinuous Processes in the Evolution of the Bacterial Genome

Abstract

Much of the change that takes place in genomic DNA in the course of evolution appears to be gradual in the sense that it is brought about by the sequential accumulation of individual single-base-pair replacements. However, changes of a more drastic type also take place, changes that alter genomic DNA by affecting more than one base pair as a result of a single genetic event. Rearrangements occur such as inversions, transpositions, substitutions, additions, and deletions. These changes, more drastic than point mutations, have the potential of changing more than one phenotypic function as a consequence of a single rearrangement event. They also have the potential of introducing discontinuities into the processes of more gradual evolutionary change, possibly enabling leaps of multiple changes of phenotypes against a background of steady, gradual change. We need to know more about the mechanisms, consequences, and frequencies of discontinuous genomic alterations, and we need to take such discontinuous changes into account when we undertake comparative analyses of amino acid and nucleotide sequences of evolutionarily related genes.