Practice question

Outcome control by loxP orientation underpins Cre utility. Recombination between directly repeated loxP excises intervening segment as circle, often desirable for deletion. When repeats inverted, circular product cannot form because joining opposite strands flips orientation instead of deleting. After first strand exchange forming Holliday junction, resolution in inverted geometry rotates segment 180 degrees, reversing direction of coding sequences between sites. This inversion reaction is reversible as both resultant loxP sites remain in chromosome, allowing conditional invertible modules for gene expression toggling and lineage labeling relying on stable inversion instead of excision.