Final answer:
The process in which a donor bacterial cell transfers DNA to a recipient bacterial cell through a pilus is called conjugation, a form of horizontal gene transfer distinct from transformation and transduction.
Step-by-step explanation:
The process by which bacteria pass a piece of DNA from a donor bacterial cell to a recipient bacterial cell through a structure called a pilus is known as conjugation. During this process, DNA is directly transferred between prokaryotes by means of a conjugation pilus, also known as the sex pilus or F pilus, in bacteria like E. coli. The genes that encode the ability to conjugate are typically located on a piece of circular DNA called the F plasmid or fertility factor. Cells that contain the F plasmid and can form the F pilus are designated as F+ cells or donor cells, while those without the F plasmid are F- cells or recipient cells.
Conjugation is distinguished from other forms of genetic exchange such as transformation, where cells take up DNA directly from the environment, and transduction, where DNA is transferred via a bacteriophage. It is an important mechanism for horizontal gene transfer, contributing to genetic diversity and the spread of antibiotic resistance among bacterial populations.