Discussion
Which of these is not a mechanism of horizontal gene transfer in bacteria?
Answer: C
Correct answer: Binary fission
Binary fission is how a bacterium divides - it passes genes vertically, from parent to offspring, and is therefore not horizontal transfer at all. The three mechanisms of horizontal gene transfer, which move DNA between contemporaries rather than down generations, are: conjugation, by direct contact through a sex pilus; transformation, by uptake of free DNA from the environment; and transduction, by a bacteriophage. The distinction matters greatly. Vertical transfer alone would confine a new gene to one lineage, and adaptation would depend on mutation. Horizontal transfer allows a gene to spread across a population and even between species, which is why antibiotic resistance appears far faster than mutation rates would predict, and why resistance to several drugs is often acquired together on a single plasmid. It also complicates bacterial taxonomy and phylogeny, since genes need not share the history of the organisms carrying them.
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