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While the alpha and beta genera are derived from the bat viral gene pool, the gamma and delta genera are derived from the avian and pig viral gene pools.
Recombination appears to be common among deltacoronaviruses. Recombination occurs frequently in the viral genome region that encodes the host receptor binding protein. Recombination between different viral lineages contributes to the emergence of new viruses capable of interspecies transmission and adaptation to new animal hosts.
^ Lau SKP, Wong EYM, Tsang CC, Ahmed SS, Au-Yeung RKH, Yuen KY, Wernery U, Woo PCY. Discovery and Sequence Analysis of Four Deltacoronaviruses from Birds in the Middle East Reveal Interspecies Jumping with Recombination as a Potential Mechanism for Avian-to-Avian and Avian-to-Mammalian Transmission. J Virol. 2018 Jul 17;92(15):e00265-18. doi: 10.1128/JVI.00265-18. Print 2018 Aug 1. PMID 29769348