• exon
  • Several types of different alternative splice forms exist including exon skipping, differential splicing of exons at their 3'- or 5'-end, intron retention, and mutually exclusive splicing. (biomedcentral.com)
  • The first type is exon skipping, in which an exon, also called cassette exon, is spliced out of the transcript together with its flanking introns. (biomedcentral.com)
  • The fourth type is intron retention in which part of an exon is either spliced (like a regular intron) or retained in the mature mRNA transcript. (biomedcentral.com)
  • It is a process through which two or more exons from different genes can be brought together ectopically, or the same exon can be duplicated, to create a new exon-intron structure. (wikipedia.org)
  • Exon shuffling was first introduced in 1978 when Walter Gilbert discovered that the existence of introns could play a major role in the evolution of proteins. (wikipedia.org)
  • What is clear now is that the eukaryotic exon-intron structure is not static, introns are continually inserted and removed from genes and the evolution of introns evolves parallel to exon shuffling. (wikipedia.org)
  • In order for exon shuffling to start to play a major role in protein evolution the appearance of spliceosomal introns had to take place. (wikipedia.org)
  • This was due to the fact that the self-splicing introns of the RNA world were unsuitable for exon-shuffling by intronic recombination. (wikipedia.org)
  • exons
  • Additionally exons can be classified into nine different groups based on the phase of the flanking introns (symmetrical: 0-0, 1-1, 2-2 and asymmetrical: 0-1, 0-2, 1-0, 1-2, etc. (wikipedia.org)
  • Symmetric exons are the only ones that can be inserted into introns, undergo duplication, or be deleted without changing the reading frame. (wikipedia.org)
  • It was noted that recombination within introns could help assort exons independently and that repetitive segments in the middle of introns could create hotspots for recombination to shuffle the exonic sequences. (wikipedia.org)
  • Evolution of eukaryotes is mediated by sexual recombination of parental genomes and since introns are longer than exons most of the crossovers occur in noncoding regions. (wikipedia.org)