Among RNA-coding genes are those for ribosomal and transfer RNAs. The study of rRNA genes has been important in evolution, especially for ancient lineages since rRNA tends to be conserved over long periods of time. Transfer RNA genes exist in multiple copies and their location is an interesting problem, but it will not be discussed in this paper. I will discuss the problem of locating protein-coding genes. I define an EXON as a contiguous segment of DNA which corresponds to a functional RNA molecule.
Some authors consider an exon as only the protein-coding part.