Hfr cell
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A hfr cell (also called hfr strain) is a bacterium with a conjugative plasmid (often F) integrated into its genomic DNA. Hfr is the abbreviation for high frequency recombination. Unlike a normal F+ cell, hfr strains will, upon conjugation with a F- cell, attempt to transfer their entire DNA through the pilus to the F- cell. As fragile a structure as a pilus will, however, likely break, and so the transfer is rarely complete. Thus, the F- cell uses only part of the genomic DNA of the F+ cell for recombination.