The Ac-Ds system in maize (Zea)

 The Dissociator locus (Ds) is on Chromosome 9, which also carries the c locus for seed color where c+ produces a colored seed coat and c a colorless seed. The Ds and c alleles have been placed in trans, so that the c+ allele is linked to the Ds allele (the Dissociator element), and the c alleles is linked to the Ds+ allele (absence of the Dissociator). The Ac locus is on a different chromosome.

[Top figure] In the absence of an Ac activator element, the Ds Dissociator element is not expressed. In a c⁺c heterozygote, wild-type c⁺ dominates c and the tissue is colored.

   [Bottom figure] In the presence of an Ac element, activation of the Ds element can induce chromosome breaks in single cells .Breakage at the the Ds locus causes loss of the distal c+ locus on an acentric fragment.  In the c⁺c heterozygote, this allows c to be expressed as a colorless (yellow) patch against a colored background. Each colorless patch arises from a separate chromosome break in a single cell, which then proliferates. If the break occurs early in development of the seed, the patches are larger; if later, then they are smaller.