Two RNA genomes are packaged into each retrovirus particle, but, after an infection, each virus generates only one provirus.  After infection, reverse transcription occurs and this process is accompanied by recombination.  Recombination involves template strand switching between the two genome copies (copy choice recombination) during reverse transcription.  From 5 to 14 recombination events per genome occur at each replication cycle.  Genetic recombination appears to be necessary for maintaining genome integrity and as a repair mechanism for salvaging damaged genomes.