What Reassorts When Reovirus Genome Segments Reassort?

The members of several families of RNA-containing viruses possess segmented genomes that consist of from 2 to 12 genome segments. These viruses have the problem of assembling their genome segments into sets that contain one of each, a process that is usually referred to as assortment. Viruses appear to solve this problem in two ways, exemplified by influenza virus, on the one hand, and by reovirus, on the other. Influenza virus possesses eight species of negative stranded genome segments, each tightly associated with the nucleocapsid protein NP(1).