ABSTRACT
Recombination and transposition have similar outcomes, both resulting in the rearrangement of DNA segments within a genome. The Holliday and Meselson–Radding models describe recombination between two homologous, double-stranded molecules, ones with identical or nearly identical sequences. The central feature of these models is formation of a heteroduplex resulting from the exchange of polynucleotide segments between the two homologous molecules. The double-strand break model provides an opportunity for gene conversion to take place during recombination. Homologous recombination occurs in all organisms, but, as with many aspects of molecular biology, the initial progress in understanding how the process is carried out in the cell was made with E. coli. Two distinct recombination systems have been described, these being the RecBCD and RecFOR pathways, with RecBCD apparently being the most important in the bacterium. From the human perspective, the most important retroelements are the retroviruses, which include the human immunodeficiency viruses that cause HIV/AIDS and various other virulent types.
