Why Evolution Works: Biological Genome Rewriting

James Shapiro (University of Chicago)

The conventional evolutionary wisdom is that genomic changes are random replication errors and natural selection guides the emergence of novel adaptive traits. However, cytogenetic and molecular biological studies since the 1940s established that virtually all genome changes result from action by specific cellular biochemical systems. For example, multiple antibiotic resistance in bacteria generally does not arise mutationally but results from cell-to-cell transfer by genome elements that carry multiple inserted DNA sequences encoding proteins that inactivate or expel specific antibiotics. Barbara McClintock discovered transposable “controlling elements” in maize that move from one genomic location to another (transpose) in the 1940s, and DNA sequence analysis has shown eukaryotic regulatory networks are formed by the insertion of transposable elements carrying similar expression sequences near genetic loci encoding network components. Recently, the capacity of germ line cells from almost all eukaryotes to undergo multisite chromosome rearrangements within a single cell division cycle has been widely documented and labelled “chromoanagenesis.” What we do not know is whether these powerful tools for biological innovation operate blindly or are somehow biased towards functional novelties. This is a question to answer experimentally. Knowing some of the triggers for evolutionary genome change allows us to find the answers.