Firstly, some textbook definitions: Conjugation : The form of gene transfer and recombination in bacteria that requires direct cell to cell contact. Plasmid : A circular Double Stranded DNA molecule that can existand replicate independently of the chromosome or may be integrated with it. A plasmid is stably inherited, but is not required for the host cell's growth and reproduction. F Factor : The fertility factor, a plasmid that carries genes for bacterial conjugation and makes its E. coli host cell the gene donor during conjugation. Conjugation is where an F+ bacterium (A bacterium with the F Factor in it) encounters an F- bacterium, and a temporary bridge (called the Sex Pilus) forms between the two cells where the F Factor Plasmid copies itself into the F- bacterium. Thereby resulting in two F+ bacteria. That is essentially what conjugation is. What makes it more interesting is the fact that other genes can be put onto the plasmid, allowing propagation of those genes, horizontally through the bacterial population as well as vertically (ie: Passed on to brothers and sisters, rather than just down to the kids). Another thing which makes it more interesting/confusing, is the fact that some F Plasmids can integrate themselves into the chromosome of their host bacteria. These results in 1. Sometimes during excision from the host chromosome, the plasmid is removed with host chromosome in it. in this way host chromosome can be spread to other bacteria. and 2. Sometimes the conjugation occurs while the plasmid is in the chromosome, and so the cell attempts to copy its whole chromosome across to the F- recipient cell. This is either never, or at the extreme, highly unlikely to occur, but what does happen, is some of the plasmid gets copied, and a chunk of the host chromosome gets copied. The recipient cell therefore gets bits and pieces, but nothing complete. If you want me to go into any more detail on any of these points, just ask for it.