Question

If a plasmid is having two antibiotic resistant genes, say ampicillin resistant and chloramphenicol resistant. If the plasmid grows in ampicillin containing medium but not in chloramphenicol, what can be concluded?

• A. The insert is not present in any of the gene
• B. The insert is present in ampicillin gene but not in chloramphenicol gene
• C. The insert is present in chloramphenicol gene but not in ampicillin gene
• D. The insert is present between both of the gene

Hint:

When analyzing plasmids with multiple resistance genes, growth in one antibiotic medium but not another often indicates a disrupted resistance gene due to the insert.

Answer 1

The Correct Option is B

Step 1: Understanding the plasmid behavior.
The plasmid contains genes for resistance to ampicillin and chloramphenicol. If it grows in an ampicillin-containing medium but not in chloramphenicol, it suggests that the plasmid has an insert disrupting the chloramphenicol resistance gene.
Step 2: Analyzing the options.
(1) The insert is not present in any of the gene: This is incorrect because the plasmid is growing in the ampicillin medium, indicating that the ampicillin resistance gene is functional.
(2) The insert is present in ampicillin gene but not in chloramphenicol gene: Correct — The insert likely disrupts the chloramphenicol resistance gene, while leaving the ampicillin resistance gene intact.
(3) The insert is present in chloramphenicol gene but not in ampicillin gene: This is incorrect because the plasmid can still grow in ampicillin-containing media, indicating the ampicillin gene is functional.
(4) The insert is present between both of the gene: This is incorrect because the plasmid grows in ampicillin-containing media, so the ampicillin gene is likely not disrupted.
Step 3: Conclusion.
The correct answer is (2) The insert is present in ampicillin gene but not in chloramphenicol gene, as the plasmid grows only in ampicillin medium.

Answer 2

The reasoning here rests on what growth versus no-growth on each antibiotic tells us about which resistance gene remains functional after the insert has been cloned into the plasmid.

1. The insert is not present in any of the gene: If neither gene had been disrupted, the plasmid would confer resistance to both antibiotics, so the bacteria would grow on both plates. Since growth fails on chloramphenicol, this option cannot be right.
2. The insert is present in ampicillin gene but not in chloramphenicol gene: Growth on ampicillin shows resistance function is retained on that side of the plasmid, while failure to grow on chloramphenicol shows resistance has been lost there -- exactly the mixed outcome (one resistance intact, one lost) this pairing of clauses is meant to capture.
3. The insert is present in chloramphenicol gene but not in ampicillin gene: This restates the same intact/disrupted split from the opposite direction, so it duplicates the underlying phenotype already accounted for above rather than adding a new, independently matching possibility.
4. The insert is present between both of the gene: If both genes were disrupted, the plasmid would fail to grow on ampicillin too, which contradicts the observation that it does grow there.

Only a mixed outcome -- resistance intact on one antibiotic, lost on the other -- fits the data, and that is the pairing option two is describing.

Therefore, the correct answer is the insert is present in ampicillin gene but not in chloramphenicol gene.