Intron

Definition

A non-coding nucleotide sequence within a eukaryotic gene that is transcribed into pre-mRNA but excised during RNA splicing and therefore absent from the mature, functional RNA product. Introns separate exons, the coding sequences that are retained and joined together to produce the final transcript. The presence, position, and length of introns vary widely among taxa and can serve as phylogenetic markers; some arthropod lineages show dramatic intron loss or gain compared to vertebrates.

Etymology

From 'intragenic region,' shortened to intron, coined to describe a region inside a gene.

Example

Comparative analysis of intron positions in the wingless (wg) gene across Lepidoptera reveals conserved splice sites useful for resolving deep relationships within the order, while some dipteran lineages have experienced extensive intron loss.

Related Terms

• exon
• splicing
• pre-mRNA
• gene
• Transcription
• RNA processing
• molecular systematics
• cis-regulatory element

Usage Notes

Intron is often used interchangeably for the DNA sequence in the gene and the corresponding RNA sequence in the transcript. Introns should not be confused with intergenic regions (sequences between genes). In arthropod molecular systematics, intron presence/absence characters and intron length polymorphisms are increasingly used alongside traditional sequence data. Some introns harbor regulatory elements or encode functional RNAs (snoRNAs, miRNAs), so 'non-coding' does not always mean 'non-functional.'