Conjugation in bacteria is best described as:

• A. Sexual reproduction by binary fission
• B. Horizontal gene transfer via transduction
• C. The exchange of DNA during transformation
• D. The transfer of genetic material to another cell using pili

Answer: (D)

Conjugation is direct DNA transfer from one bacterial cell to another through physical contact mediated by a sex pilus. A donor cell, often carrying the F plasmid, forms the pilus and establishes a mating bridge to a recipient, through which genetic material is moved. This is a form of horizontal gene transfer that requires live cells and cell-to-cell contact, and it can transfer plasmid DNA or, when the F factor is integrated, chromosomal DNA segments as well.

This mechanism is distinct from binary fission, which is how bacteria reproduce asexually; from transduction, which uses a bacteriophage to shuttle DNA between cells; and from transformation, which involves uptake of free DNA from the environment.