Final answer:
The description that best fits Activator (Ac) and Dissociation (Ds) transposable elements in maize is that Ac contains a functional transposase gene necessary for transposition, while Ds lacks this gene and relies on Ac for mobility. These discoveries by Barbara McClintock have greatly informed our understanding of genetic regulation.
Step-by-step explanation:
The correct answer that describes the role of the Activator (Ac) and Dissociation (Ds) transposable elements in maize (corn) is b. Ac contains a functional transposase gene; Ds lacks a functional transposase gene.
The Ac element is an autonomous transposable element and has the gene necessary for producing the enzyme transposase, which enables it to move independently within the genome. On the other hand, the Ds element is a non-autonomous transposable element because it lacks the functional transposase gene necessary for its mobility. Therefore, for Ds to transpose, it requires the presence of an Ac element to provide the needed transposase.
These transposable elements were discovered by Barbara McClintock through experiments on maize that showed Ac can mobilize itself and a nearby Ds element, causing genetic changes such as the inactivation of a normal Bz gene, leading to a variation in kernel color. This Ac/Ds system highlights the genetic mechanism behind the phenomenon of jumping genes and has significantly contributed to our understanding of genome plasticity and the regulation of gene expression.