A eukaryotic gene consists of both coding and non-coding nucleotide sequences. The coding sequences are called exons and non-coding sequences are called introns. Introns are rare in prokaryotic genes.

In humans, up to 35% of the sequenced genome corresponds to intronic sequence, while exons cover around the 2.8% of the genome1. The presence of exons and introns in eukaryotic genome is believed to be evolutionarily beneficial because it allows the production of multiple proteins from the same gene through alternative splicing and may accelerate the creation of novel proteins through exon shuffling2.

An easy way to remember exons and introns is exons are expressing sequences whereas introns are interrupting or intervening sequences.

Difference between Exon and Intron



Present In both prokaryotes and eukaryotes

Present in eukaryotes and rare in prokaryotes

Exons are expressing sequences

introns are interrupting or intervening sequences present between exons

Nucleotide sequence that codes for protein

Nucleotide sequence that does not code for protein

Exons are Interrupted by introns

Introns are found between exons

Retained in mature mRNA

Removed from pre-mRNA during RNA splicing

Typically, less than 100 nucleotides

Typically, larger than exons, can be thousands of nucleotides long

Highly conserved with very few mutations as it codes for a specific protein.

Less conserved with many mutations as mutations does not affect the protein sequence.

The function of exon is to determine the structure and function of the protein.

Introns exact function is not fully understood, but they are thought to play a role in regulating gene expression by alternative splicing and maintaining the integrity of the genome.


  • Rigau M, Juan D, Valencia A, Rico D (2019) Intronic CNVs and gene expression variation in human populations. PLOS Genetics 15(1)
  • Gorlova, O., Fedorov, A., Logothetis, C. et al. Genes with a large intronic burden show greater evolutionary conservation on the protein level. BMC Evol Biol 14, 50 (2014).
  • Sakharkar, M. K., Chow, V. T., & Kangueane, P. (2004). Distributions of exons and introns in the human genome. In silico biology4(4), 387-393.


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