Although in many cases adjacent exons are joined during the splicing reaction, in some cases exons can be skipped or cryptic splice sites activated, resulting in alternatively spliced transcripts.

More information: Cristian Prieto-Garcia et al, Pathogenic proteotoxicity of cryptic splicing is alleviated by ubiquitination and ER-phagy, Science (2024). DOI: 10.1126/science.adi5295 ...

The remaining 209 clusters (186 genes) had unequivocal alternative splicing events, with cryptic exons, 5′ exon extensions and 3′ exon extensions occurring in roughly equal proportions.