Final answer:
The Ac element is an autonomous transposable element because it contains and can express the transposase enzyme required for its mobility within the genome. In contrast, the Ds element lacks this gene and is thus non-autonomous, relying on the Ac element to provide the necessary transposase for transposition.
Step-by-step explanation:
The autonomous transposable element (TE) between the Ac and Dc elements is the Ac element. It is considered autonomous because it contains the gene for a transposase enzyme, which is necessary for the cut-and-paste mechanism of transposition. This means the Ac element can mobilize itself within the genome without assistance. In contrast, the Ds element lacks this gene and thus cannot transpose independently; it is considered non-autonomous and requires the transposase provided by an autonomous element like Ac to move.
The presence of 11 bp inverted repeats and 8 bp direct repeats associated with both the Ac and Ds elements shows structural similarity, supporting their common ancestry. This structural configuration is important for the transposition process. Additionally, the versatility and presence of transposable elements like the maize Ac (activator) gene in various species allude to their significant evolutionary role and potential for horizontal gene transfer.