Through the year of 1960s, the gene was clearly explained as the region of DNA which gives increase to a single polypeptide or to a one RNA for genes whose final product is RNA not protein, example for. Ribosomal RNA genes. The existence of operons in prokaryotes did not challenge this concept because, although several clustered genes produced a one polycistronic mRNA, one could still recognized one DNA regions as genes based on the distinct polypeptides they encoded. The concept even accommodated the discovery in which various protein- coding genes in eukaryotes comprise coding regions (exons) separated by noncoding sequences (introns) since, again, only single polypeptide was encoded by this region of DNA. More recently, moreover, other mechanisms have come to light in eukaryotic cells that can lead to a various of polypeptides being produced from a one DNA sequence; for instance alternative RNA splicing substitute polyadenylation sites and RNA editing. Nevertheless, in each of these cases the protein products are closely related through sequence and all are derived from the same single region of DNA. Thus the original definition perhaps needs tweaking to indicate in which a protein-coding gene is a region of DNA which encodes a one polypeptide or a group of closely- related polypeptides but otherwise the definition is intact. The substitute scenario to regard a one DNA sequence which gives rise to say 10 closely- related polypeptides by post-transcriptional processing as representing 10 genes would certainly not fit in with accepted practice.