A cell infected with influenza A/WSN/1933 (H1N1) virus with four, of the eight, influenza viral RNA segments identified by fluorescent in situ hybridization: PB2 (red spots), PB1 (green spots), PA (magenta spots), and NP (yellow spots). The nucleus is labeled in blue with a nuclear dye. Viral RNA segments are made in the nucleus and move to the edge of the cell (plasma membrane) for packaging into virus particles. The segments come together as unique complexes inside the cell to ensure packaging of all eight segments into a virus particle. Reassortment of the genetic material between flu strains will happen within these complexes.