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Bacterial conjugation. Artwork showing genetic material being transferred from one bacteria to another, a process known as conjugation. A circular piece of DNA (deoxyribonucleic acid), known as a plasmid, is passed from the donor bacterium (top left) through an enlarged pilus (hair-like bridge) to the recipient bacterium (bottom left). Once transferred, the plasmid genes are incorporated into the recipient's DNA. Plasmids often carry genes for beneficial traits such as antibiotic resistance. (KEYSTONE/SCIENCE PHOTO LIBRARY/FRANCIS LEROY, BIOCOSMOS)