Mechanism of chromosome transfer

If the Hfr or F⁺ donates its chromosome to F^- during conjugation, the donor should actually die after conjugation. But this does not happen. There is evidence that Hfr chromosome replicates shortly before or during conjugation and only one of the two strands is transferred to F^- cell and gets replicated there. This leaves a complete chromosome in Hfr or F⁺ even after conjugation.