Switch in serotype Y to serotype B by a relapsing fever Borrelia spp

A serotype Y cell with two linear plasmids. The one on the top bears several different vmp genes that are silent. These are vmpP, vmpY, vmpB, and vmpG. The second linear plasmid has a second copy of the vmpY. It is at the end of the plasmid and is expressed off a promoter (P) at the site. The serotype identity of the cell is determined by the vmp gene on the second plasmid. In the switch, one of the silent vmp genes on the first plasmid--in this case vmpB--replaces the vmp gene at the expression site on the second plasmid. There is no loss of a silent vmp gene during the switch. Now that the vmp gene is replaced on the second plasmid, the cell's identity is serotype B.