eukarüootsete geenide DNA-aluste vahejärjestused, mida ei esine töödeldud RNA-transkriptis, kuivõrd nad lõigatakse splaissingul primaarsest RNA-transkriptist välja, An intron is any nucleotide sequence within a gene that is removed by RNA splicing while the final mature RNA product of a gene is being generated. The term intron refers to both the DNA sequence within a gene and the corresponding sequence in RNA transcripts. Sequences that are joined together in the final mature RNA after RNA splicing are exons.

a sequence of DNA inserted within a gene that is not part of the coding sequence and is therefore not represented in the messenger RNA. Many, though not all, eukaryotic structural genes contain these sequences. They have not, however, been found in bacterial genes.