List three mechanisms of horizontal gene transfer in bacteria and describe how DNA is transferred between cells in each type of transfer.

a) Conjugation: DNA transfer through direct cell-to-cell contact using a sex pilus; Transformation: Uptake of free DNA from the environment; Transduction: DNA transfer via bacteriophages.
b) Conjugation: Uptake of free DNA from the environment; Transformation: DNA transfer through direct cell-to-cell contact using a sex pilus; Transduction: DNA transfer via bacteriophages.
c) Conjugation: DNA transfer via bacteriophages; Transformation: DNA transfer through direct cell-to-cell contact using a sex pilus; Transduction: Uptake of free DNA from the environment.
d) Conjugation: DNA transfer through direct cell-to-cell contact using a sex pilus; Transformation: DNA transfer via bacteriophages; Transduction: Uptake of free DNA from the environment.