Practice question

Conditional knockout overcomes embryonic lethality by floxing essential exons with loxP sites placed in same orientation flanking critical region intronically, preserving normal splicing without Cre. Excision occurs only upon Cre expression which recombines directly repeated loxP sites, deleting intervening exon and creating frameshift or null allele. Tissue specific or tamoxifen inducible Cre drivers then restrict deletion temporally and spatially. Requirement of same direction loxP ensures deletion rather than inversion, producing irreversible loss of function in selected cells only in vivo efficiently.