Breakpoint frequency in near full-length BC and BF recombinants. The breakpoint positions are based on the HXB2 numbering. Left and middle grey regions: genomic regions where breakpoints are less present in BC than BF recombinants. Right grey region: both BC and BF recombinants have few breakpoints within a segment of gp120. Vertical bars: the frequency of sequences with a breakpoint at that sequence position. Horizontal red lines: exactly 3 sequences sharing the breakpoint. Note that the frequency scales are different in each panel in order to maximize resolution.