a-b, Inter-segment RNA interaction maps for two parent strains, PR8 (H1N1) and Udorn (H3N2), and c, a reassortant of PR8 that bears the Udorn PB1 and NA gene segments, PR8::Udorn(PB1+NA) (H1N2). Interactions are coloured according to the parent strain that donated the interaction and shaded according to their interaction frequency, as indicated above (see Figure 2). PR8, A/Puerto Rico/8/34; Udorn, A/Udorn/307/72.