A composite transposon such as Tn10 carries a tetracycline resistance gene. Its ability to move between plasmid and chromosome depends on which structural arrangement?

• A A single gene encoding both transposase and resolvase within the resistance cassette
• B Direct repeats of the target site generated after insertion
• C Two insertion sequence elements flanking the resistance gene in the same orientation ✓
• D A long terminal repeat recognised by host RNA polymerase

Explanation

Composite transposons consist of a central segment carrying resistance or metabolic genes flanked by two insertion sequence (IS) elements. The IS elements supply the transposase that catalyses movement as a unit. Direct repeats of the target site are a consequence of insertion, not the motive machinery, and long terminal repeats are features of retroviruses, not bacterial DNA transposons.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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