Practice question

Outcome of Cre-loxP recombination depends strictly on relative orientation and location of loxP sites. When two loxP sites in same DNA molecule are oriented in same direction, Cre excises the intervening segment as a circular product leaving one loxP scar. When loxP sites are in opposite orientation, Cre does not delete but reverses the strand polarity between them, inverting the intervening sequence. This inversion property underlies Cre-FLEX and DIO systems where gene orientation flips reversibly, enabling conditional activation, silencing and lineage tracing applications in neuroscience.