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#inversion

2 public questions tagged with this topic.

Recombination

Orientation of loxP sites in inverted direction leads to

When two loxP sites reside on same DNA molecule in inverted orientation, Cre recombinase still forms tetrameric synapse but alignment is antiparallel, causing exchange to flip intervening segment rather than delete it. Cleavage in spacer region and rejoining in opposite direction inverts DNA between sites, retaining both loxP sites on chromosome with reversed orientation of internal sequence. This principle underlies generation of invertible gene traps, switching cassettes, and orientation-specific lineage tracing. Inversion is reversible because sites remain, allowing repeated flipping if Cre

Ref: Lodish et al., Molecular Cell Biology, 9th ed., Chapter 8: Inversion Outcome of Inverted loxP Sites

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Gene Tar getting

What is essential for inversion to happen in Cre-lox system?

In Cre-loxP system Cre binds 13 base pair inverted repeats surrounding 8 base pair asymmetric core of loxP. For inversion versus deletion decision, relative direction of core determines outcome. When core sequences point towards each other on same chromosome, meaning loxP sites in opposite orientation, Cre catalyzed recombination reverses intervening segment without loss. Direct repeats cause deletion. Thus requirement for inversion is antiparallel loxP orientation ensuring DNA strand exchanged leads to reversal rather than circular excision, employed in FLEX switches for reversible gene contr

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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