Sister shows, also known as companion series,[1][2] are two or more television series which exist in the same fictional universe and which may have crossovers. They differ to a degree from spin-offs, in that they are established independently from one another. The popularity of most series is limited to a few seasons, and sister shows allow expanding the immediate audience and ratings share. This is accomplished by using mostly different actors and production facilities. Sister shows often shift styles or target audience slightly, for a larger overall market. Thus The Beverly Hillbillies emphasizes slapstick, while Green Acres emphasizes surreal humor.
Stargate Atlantis premiered during the eighth season of Stargate SG-1. Both occasionally had crossover plots. Stargate Universe likewise featured crossover character appearances.
Deep Space Nine began during the sixth season of The Next Generation. Several characters from the older series appeared in the newer, but only one episode of the older ("Birthright") had characters from the newer. All the Star Trek series are in the same universe, and there were many shared concepts and characters.
All three take place around the town of Hooterville. Guests appear in Green Acres, although the plots are not linked.
The Trumptonshire series had Camberwick Green, Trumpton and Chigley villages in the same area. Gordon Murray stated that the area of "Trumptonshire" is "representative of real locations which are one-and-a-half miles from each other in an equidistant triangle".[3] Several characters appear in guest roles in other villages.
Known for frequent crossovers, the latter was planned by William J. Bell to be a sister show. Characters have gone between the two series regularly since the 1990s.
Although The X-Files and The Lone Gunmen are explicitly linked, mostly through several shared characters and plot threads, the connection to Millennium is only concretely expounded in one episode of The X-Files and one episode of Millennium.
