Final answer:
Myc is a transcription factor that can target a large percentage of genes in the genome, reflecting the complexity seen in eukaryotic genomes with much more DNA than needed for just the genes.
Step-by-step explanation:
The Myc protein is a transcription factor that is known to regulate a large number of genes within the genome. While the exact percentage of genes targeted by Myc can vary depending on the cell type and physiological context, it is recognized that Myc can influence a significant portion of the genome. Given that eukaryotic genomes consist of much more DNA than necessary to account for the number of genes, studies like those done by Britten and Davidson using renaturation kinetics experiments have shed light on the understanding of DNA content, genes, and the 'extra' non-coding DNA.
Earlier estimates suggested that it might take up to 100,000 genes to make organisms like humans or mice, but current science has shown it takes fewer. Yet the existence of extra DNA beyond what is needed for those genes has been a point of much research. In context with the question, while it's difficult to give a precise percentage target by Myc without referencing specific research, what's clear is that Myc has the capability to regulate a wide array of genes across the genome, possibly even up to thousands, given the scale of eukaryotic genomes.