The F plasmid is a self-transmissible plasmid found in some strains of E. coli. Cells that possess one or more copies of the F plasmid are called F+; cells lacking the F plasmid are called F-. The animation illustrates several stages in the transfer of the F plasmid from F+ to F- cells.

1. F+ cells contain at least one copy of the F plasmid and carry sex pili on their surface.

2. After the sex pilus attaches to an F- cell, the pilus retracts, bringing the F- cell into contact with the F+ cell.

3. The F plasmid replicates, leaving one copy of the plasmid in the F+ cell and transferring a newly synthesized copy into the F- cell.

4. After plasmid transfer, the recipient cell becomes F+. This cell now begins to synthesize sex pili and can in turn transfer F plasmids to other cells.

Suggested use: Demonstrate the animation several times in class, explaining the different processes involved, and allow students to access the animation for review.