For many decades, H1N1 influenza in North American swine (also called “classical” H1N1) mutated relatively slowly [9], but in 1997, a novel reassortant emerged that contained three segments (HA, NA, and PB1) from the human H3N2 virus, and the remaining five from the classical North American H1N1. The gene discussed is XK; the disease is swine influenza.