What are exons?

Exons are the regions of an RNA transcript, or the DNA encoding it, that remain in the mature RNA after introns have been removed by RNA splicing. In a mature mRNA, the exons can include both the protein-coding sequence, and the 5’ and 3’ untranslated regions. Exons occupy a very small portion of the whole genome. For instance, only 1.1% of the human genome is spanned by exons, whereas 24% is introns and 75% is intergenic DNA.