Discussion
The F plasmid in Escherichia coli is responsible for
Answer: A
Correct answer: the ability to act as a donor in conjugation
The F or fertility plasmid carries the tra genes, which encode the sex pilus and the machinery of DNA transfer, so a cell possessing it can act as a donor in conjugation. The states are worth distinguishing. An F+ cell carries the plasmid free in the cytoplasm and transfers a copy of it to an F− recipient, which thereby becomes F+ - the plasmid spreads through a population like an infection. An Hfr cell has the plasmid integrated into the chromosome and transfers chromosomal genes in a fixed linear order. An F’ cell carries a plasmid that has excised imprecisely, taking a few chromosomal genes with it. The Hfr state is the basis of interrupted mating experiments, in which conjugation is broken off at intervals and the order in which markers appear gives their order on the chromosome - the first genetic map of E. coli was constructed this way. Antibiotic resistance is carried by R plasmids instead.
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