Practice question

Ac and Ds controlling elements discovered by Barbara McClintock constitute first defined transposable system residing in maize genome regulating mutable loci affecting kernel color variegation. Ac Activator autonomous element encodes transposase located on chromosome, while Ds Dissociation lacks transposase but retains responsive termini. Both exist as DNA transposons inserting near chromosome breakage sites on chromosome 9 causing variegated phenotypes. Their behavior established concepts of autonomous versus non-autonomous elements, regulation by copy number, and relationship between chromosome breakage and transposition observed in maize breeding experiments.