Practice question

Ds element is non-autonomous relative of Ac that arose via internal deletion removing significant portion of transposase coding region while retaining intact 11 bp terminal inverted repeats and subterminal binding sequences required for transposase recognition. Consequently Ds cannot produce functional transposase and remains stable until Ac provides enzyme in trans for excision and reintegration. This dependence underlies classical variegated kernel phenotype where Ds insertion causes chromosome breakage only when Ac present, illustrating paradigmatic autonomous-nonautonomous interaction regulating mutable alleles and genome instability in maize.