Define conjugation in bacterial genetics.

• A. Conjugation is direct transfer of DNA between bacteria via pili.
• B. Conjugation is DNA transfer by bacteriophages.
• C. Conjugation is uptake of naked DNA from the environment.
• D. Conjugation is genetic recombination during transformation.

Answer: (A)

Conjugation is a mode of genetic exchange in bacteria that requires close contact between cells. It uses a sex pilus to form a direct bridge that allows transfer of DNA from a donor to a recipient. The donor typically carries a fertility factor (F plasmid) that encodes the pilus and the transfer machinery. A single strand of DNA is nicked and moved through the pilus into the recipient, while both cells synthesize the complementary strands to restore double-stranded DNA. This direct, cell-to-cell transfer distinguishes conjugation from other forms of DNA uptake, such as transformation (uptake of free DNA from the environment) and transduction (DNA movement by bacteriophages). If the F plasmid is integrated into the chromosome, chromosomal genes can also be transferred during conjugation, a scenario known as high-frequency recombination, but the fundamental idea is the direct DNA transfer via pili.