Final answer:
The answer is 'a) Different loci; the same loci'. Trans-acting elements, such as transcription factors, operate at different genomic loci, while cis-acting elements, such as promoters, are situated in the same loci immediately adjacent to the genes they control.
Step-by-step explanation:
Mutations in trans-acting elements typically occur in different loci, while mutations in cis-acting elements occur in the same loci. The correct answer to your question is 'a) Different loci; the same loci'. Trans-acting elements such as transcription factors can bind to DNA sequences at locations that are distant from the genes they regulate. In contrast, cis-acting elements, like promoters, are located immediately adjacent to the genes they control and are part of the same DNA locus.
For instance, when transcription factors bind to the promoter just upstream of the encoded gene, it is considered a cis-acting element. Conversely, transcription factors may also bind to enhancers, which can be located far away from the gene they influence. These enhancers help increase the efficiency of transcription, interacting with a variety of proteins and helping to form the transcriptional machinery necessary to initiate the process.