Question

Why does transposition always produce direct repeats in the chromosomal DNA?

Short answer

Transposition leads to direct repeats in the chromosomal DNA due to the mechanism of transposition. During insertion of the transposon at the target site, single-stranded overhangs on the target DNA are filled in by DNA polymerase, leading to the duplication of the sequence next to the transposon, hence creating direct repeats on both sides of it.

Step-by-step solution

Understand the Process of Transposition

Transposition refers to the movement of DNA segments, called transposons, within the genome. When a DNA sequence is cut out from one location and inserted into another location in the genome, it is known as transposition. The transposon is not copied, unlike in the process of replication.

Role of Enzymes in Transposition

The process of transposition is facilitated by enzymes called transposases. These transposases interact with the ends of the transposon and the target DNA site. They cut the DNA at the target site, creating staggered breaks. This gives rise to single-stranded overhangs on the both the target DNA and the transposon.

Formation of Direct Repeats

The transposon is then inserted at the target site, and the single-stranded overhangs on the target DNA are filled in by DNA polymerase. This results in the duplication of the sequence flanking the transposon, creating direct repeats on either side of it.