The genotypes of the bulk virus populations passaged in MDCK-V2 cells and selected by cell sorting (populations VS1 to VS6) were analyzed by deep sequencing of virion RNA on the Illumina platform, using viruses from one of the populations passaged in MDCK cells and sorted in parallel after infection of A549/pr(IFN-β).GFP cells as a control (population MS). The gene discussed is IFNB1; the disease is infection.