Question

Given below are two statements :
Statement (I) : Insertion Sequences (IS) are short DNA sequences (800-1400 bp) and have the ability to transpose.
Statement (II) : IS also promotes recombination between non-homologous chromosomes.

• A. Both Statement (I) and Statement (II) are correct.
• B. Both Statement (I) and Statement (II) are incorrect.
• C. Statement (I) is correct but Statement (II) is incorrect.
• D. Statement (I) is incorrect but Statement (II) is correct.

Hint:

IS elements are simple transposable bacterial elements (800–1400 bp) encoding only transposase. Because they are present in multiple identical copies, they act as portable regions of homology, facilitating chromosomal crossovers and rearrangements.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Insertion sequences (IS elements) are the simplest class of transposable elements (transposons) found in bacteria.
They carry only the genetic information necessary for their own transposition.

Step 2: Detailed Explanation:
Let us analyze both statements regarding Insertion Sequences:
- Statement (I) is correct: Insertion sequences are small, simple transposable elements, typically ranging from 800 to 1400 base pairs in size.
They consist of a central gene encoding the enzyme transposase, flanked on both sides by short inverted terminal repeats that are recognized by the transposase during the transposition process.
- Statement (II) is correct: Multiple copies of identical insertion sequences are often dispersed at different loci throughout a cell's genome.
Because they share identical sequences, these dispersed IS elements can undergo homologous recombination.
When homologous recombination occurs between IS elements located on different, otherwise non-homologous chromosomes, it can lead to chromosomal rearrangements such as translocations, deletions, and inversions.
Through this mechanism, IS elements promote genetic recombination and rearrangements between non-homologous chromosomes.
Therefore, both Statement (I) and Statement (II) are correct.

Step 3: Final Answer:
Both Statement (I) and Statement (II) are correct.