Another characteristic of plasmid is their loss prevention strategies, such as copy number control mechanism, active partition systems, and postsegregational killing (PSK).  
The copy number of plasmids per cells depend on the origin of replication and can vary from 2 copies for low copy plasmids to 50 to 800 for high copy plasmids\citep{M_nch_2019}. The plasmid copy number is inversely correlated with their size (and functions). For this reason plasmids are classified by their size and general abilities of motion. In general large plasmids has the ability to copy themselves to another bacteria trough conjugation. Some others rather small plasmids could be mobilized by the former but lack the machinery to do it themselves. The called non-mobilizable plasmids are conceived to be small but a large percentage of them are almost as big as conjugative plasmids, this fact still remains an open question\citep{Smillie_2010}.

HTG gene pool....