the operon concept was elucidated by Jacob and Monod to describe the transcriptional regulation of polycistronic structural genes in bacteria like E. coli . While the operon system is a hallmark of gene regulation in all prokaryotes, the sources also note that structural genes in eukaryotes are mostly monocistronic, implying that exceptions exist . Modern biological research has identified operon-like clusters in certain eukaryotes, such as some nematodes and protozoans. Therefore, the concept is broadly applicable to all prokaryotes and some eukaryotes. Mastering these nuances of gene regulation is a high-priority strategy, as NCERT textbooks serve as the primary resource for approximately 95% of NEET Biology questions .