Two RNA genomes are packaged into each retrovirus particle, but, after an infection, each virus generates only one provirus.  After infection, reverse transcription is accompanied by template switching between the two genome copies (copy choice recombination).  There are two models that suggest why RNA transcriptase switches templates. The first, the forced copy-choice model, proposes that reverse transcriptase changes the RNA template when it encounters a nick, implying that recombination is obligatory to maintaining virus genome integrity. The second, the dynamic choice model, suggests that reverse transcriptase changes templates when the RNAse function and the polymerase function are not in sync rate-wise, implying that recombination occurs at random and is not in response to genomic damage. A study by Rawson et al. supported both models of recombination. From 5 to 14 recombination events per genome occur at each replication cycle.  Template switching (recombination) appears to be necessary for maintaining genome integrity and as a repair mechanism for salvaging damaged genomes.