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.