I have a quest about Hfr plasmids. Wikipedia said that you mate an Hfr with an F- plasmid the whole thing transfers over. Is that true. I ask because I would think that the Hfr would be too big to transfer over.

In theory, yes you can transfer the entire genome, and its been done. Most often, only a portion of the genome gets transferred probably due to physical disruption sensitivity of the pilus/bridge (but work supports the idea that DNA does not travel through the pilus, but the physical connection is necessary for transfer). This is why its great for mapping/linkage analysis. I'm sure wikipedia said all this as well though...

Edited April 30, 201312 yr by Esrevinu

Thank you so much for your clarification. However I was confused when you said that DNA is not transferred through the pillus but the pillus is necessary for conjugation isn't the whole purpose of the pillus to transfer DNA, first of the plasmid, and then chromosomal?

Yes, if there is no physical contact between the pilus and the F- bacteria, the the DNA will not transfer. There is experimental evidence however, that suggests DNA is not traveling through the pilus itself, but that if there is no physical contact with the pilus and f- bacteria, there is no genetic exchange. The exact mechanism of genetic exchange is not known at this time.