Question

VISUAL SKILLS Which of the three mechanisms described in Figures 21.8 and 21.9 result(s) in a copy remaining at the original site as well as a copy appearing in a new location?

Short answer

The three mechanisms, cut-paste, copy-paste transposon mechanism, and retrotransposition result in a copy that remains at the original site and a copy that appears in a new location.

Step-by-step solution

Retrotransposons

The retrotransposons move by a copy and paste mechanism and leave a copy at the original site during transcription. They are more common and move via RNA intermediate, which is a retrotransposon DNA transcript.

The RNA intermediate is converted into ds DNA by reverse transcriptase. The synthesized dsDNA is the mobile copy of retrotransposon, which gets pasted into a new location of DNA.

Transposons

The transposon is cut out of its location and integrated into a new locationvia DNA intermediate, or it can move within a genome.It can move within a genome by a cut-and-paste or copy-and-paste mechanism.

Cut- paste or copy-paste transposon

The cut-paste or copy-paste mechanism both require a transposase enzyme which is usually encoded by the transposon.This enzyme cuts ds DNA to remove a transposon from one genomic site and incorporates it back into the DNA of the taget site, where a new cut is made.

The movement of retrotransposons involves the synthesis of ssRNA intermediate and whereas movement of transposon by cut-paste or copy-paste mechanism involves the synthesis of dsDNA intermediate.