[Unequal crossing over is the principal pathway of homologous recombination in tandem duplications of Escherichia coli]

Abstract

Homologous recombination between direct DNA repeats in tandem duplications usually leads to their dissociation. An even number of crossovers between two copies of a duplication should lead to the formation of diploid segregants, i.e., to the preservation of the duplication. However, in studies of the genotype of diploid segregants in heterozygous tandem duplications of Escherichia coli, it was shown that they arise by unequal exchanges between sister chromosomes rather than by intrachromosomal exchanges. Generally, these exchanges lead to the establishment of the homozygous state of (heterozygous) duplications. Since the available data suggest that the exchange between sister chromosomes may be coupled with DNA replication, it is supposed that unequal exchanges between direct DNA repeats occur in the process of DNA replication.