Introduction to Genetic Analysis 160

Introduction to Genetic Analysis 160 - 44200_05_p151-184...

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159 5.2 Bacterial conjugation generally stop before the farthermost genes are transferred, resulting in their being included in fewer exconjugants. How can we explain the second unusual property of Hfr crosses, that F ± exconjugants are rarely converted into Hfr or F ² ? When Wollman and Jacob allowed Hfr ³ F ± crosses to continue for as long as 2 hours before dis- ruption, they found that in fact a few of the exconju- gants were converted into Hfr. In other words, the part of F that confers donor ability was eventually transmit- ted but at a very low frequency. The rareness of Hfr ex- conjugants suggested that the inserted F was transmitted as the last element of the linear chromosome. We can summarize this with the following map, in which the ar- row indicates the process of transfer, beginning with O: Thus almost none of the F ± recipients are converted be- cause the fertility factor is the last element transmitted, and usually the transmission process will have stopped before getting that far.
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This note was uploaded on 01/10/2011 for the course BIOL BIOL taught by Professor Johnson during the Spring '08 term at Aberystwyth University.

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