[The importance of recombinations occuring in the process of DNA replication].

In the process of DNA replication in Escherichia coli, the unequal crossing over occurs between DNA direct repeats in sister chromosomes. Such exchanges lead to the formation of tandem duplications and, therefore, to an increase of gene expression. It is proposed that non-homologous cohesion of sister chromosomes and unequal crossing over occur if the movement of replication fork is stopped. In the case of the unceasing movement of replication fork the homologous exchange between sister chromosomes occurs which provides their post-replication reparation.