Accessible Version:  Using Evolution to Understand Influenza

Build a tree: An evolutionary tree is a diagram that summarizes the relationships among the viruses from different time periods. You constructed an evolutionary tree for the 11 influenza viruses based on data from the hemagglutinin gene. The tree suggests that the viruses are steadily changing across time. In other words, the virus is changing from year to year. This means that the virus that was isolated in 1968 is the most different from the virus from 2003. It also means that the virus from 2003 is most closely related to the viruses from 1997.

The following table summarizes the number of nucleotide changes between 5 of the 11 viruses using the sequence from the 2003 virus as a reference. The changes noted are from the entire nucleotide consensus sequence, which is 1,095 nucleotides long. The first column is the year a virus was isolated. The second column is the number of changes in that sequence compared with the sample from 2003.

Year the influenza virus was isolated Number of changes in the hemagglutinin region compared with the influenza virus isolated in 2003
1997 34
1992 78
1982 95
1975 128
1968 140

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