You have observed horizontal gene transfer among two closely related species of

Question

You have observed horizontal gene transfer among two closely related species of Vibrio cholerae, the causative agent of cholera-Species A and Species B. Species A is resistant to the antibiotic ciprofloxacin, whereas Species B is not. You observe that Species B can inherit ciprofloxacin resistance from Species A but you do not know the mechanism. You have devised the following experiment to test which mechanism of horizontal gene transfer is responsible. Control 1: Species A Control 2: Species B Sample 1: Species B+ Species A Sample 2: Species B + genomic DNA of Species A Sample 3: Species B+ DNA nuclease treated culture supernatant of Species (all free extracellular DNA is degraded and no Species A cells are present) You then grow your controls and samples on medium containing ciprofloxacin. You observe that Control 1 and Sample 3 grow in the presence of ciprofloxacin. Which of the following mechanisms of horizontal transfer is most likely responsible? Translocation Transformation Conjugation Transduction None of these mechanisms

Explanation / Answer

Answer is Transformation, as it is the process of uptake of short pices of naked DNA from another dead organism,where as conjugation is the uptake from living organism. Even though the supernatent was nuclease treated, a fragment of DNA is sufficient for transformation to occur and confer antibiotic resistance.Translocation is not a means of horizontal gene transfer.

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