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. 2009 Oct 7;4(10):e7366. doi: 10.1371/journal.pone.0007366

Figure 2. History overlap for segments PB1 and NP of the swine influenza strain A/Swine/Tennessee/23/1976.

Figure 2

NP and all the other segments except PB1 share a common recent history, whereas the recent history of PB1 is different from the other seven segments, indicating a reassortment event at PB1. The small history overlap of M1 with PB1 and NP at lower identities can be attributed to a possible slower evolutionary rate of M1 and a fork in its lineage to a line of human viruses. The fluctuations in the history overlap of NP at 99% identity are due to small number of sample points at that level of identity.