Fig. 2.

Timeline of emerging representative coronavirus events and their infectious clones generated using reverse genetics systems. The timeline spans from the first coronavirus in history to the emergence of 2019-nCoV in 2019. Red arrows indicate human coronavirus outbreaks and identification events. Blue arrows indicate animal coronavirus outbreaks and identification events. Green arrows indicate the publication of infectious clones using different reverse genetics methods (Almazan et al., 2000; Li et al., 2013; Thao et al., 2020; Yount et al., 2002).