Correct option is D
Explanation-
Option d:"LoxP-Cre system cannot be used to generate translocation between chromosomes."
This statement is actually FALSE (i.e., it is the incorrect statement)
The Cre-loxP system can be used to induce chromosomal translocations, provided that loxP sites are present on two different chromosomes. Many research studies have used Cre-loxP to create targeted chromosomal translocations in mouse models and in cells. If two loxP sites are placed on different chromosomes, Cre recombinase can mediate a site-specific recombination between them, resulting in a reciprocal chromosomal translocation.
Chromosomal rearrangement models in cancer research often use Cre-loxP to induce translocations.
Incorrect Options (Correct statements)
Option a: When loxP sites flanking a test sequence are oriented in the same direction, Cre mediates the excision of the intervening sequence.
When two loxP sites are in the same orientation (direct repeat), Cre recombinase excises (removes) the DNA between them, leaving behind a single loxP site. This is a classic, well-studied use of Cre-loxP in genetic engineering for deletion or excision of target DNA segments.
Option b : LoxP sites in inverted orientation around an intervening sequence lead to inversion upon action by Cre recombinase.
When two loxP sites are in opposite orientation (inverted repeats), Cre recombinase inverts the DNA segment between them. This causes the DNA between the two loxP sites to flip direction (inversion).
Option c: LoxP sites recognized by the Cre recombinase are palindromic around a spacer sequence.
Two 13 bp inverted repeat (palindromic arms) on both sides of an 8 bp asymmetric spacer. The 13 bp arms are palindromic, meaning they read the same forwards and backwards. The 8 bp spacer is asymmetric, giving the loxP site directionality, which is crucial for determining the recombination outcome.
Final Correct Answer: Option d
