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Table 1 Description and distribution of expressed retrocopy events

From: Retrocopy contributions to the evolution of the human genome

Type of event Parent gene contribution Count Percentage
Type I – Exon acquisition (host gene modified by retrocopy) New 5' exon (UTR and/or N-terminal protein coding) 10 1%
  New 3' exon (UTR and/or C-terminal protein coding) 18 2%
  New internal exon 6 1%
Type II – duplication (no host gene involved) Single exon 624 86%
  Exons/introns generated, post insertion 55 8%
Type III – novel genes (no host gene involved) Antisense, majority of ORF out-of-frame wrt to parent, and other cases (e.g., from non-genic regions) 13 2%
Total   726  
  1. Type I: retrocopy inserted into or near an existing gene. A portion of the retrocopy contributes, mostly by alternative splicing, a new sequence to a pre-existing mRNA. Type I events can be divided into cases that add new N- or C-terminal encoding exons or internal exons. Type II: duplicated gene inserted at a locus where no prior gene existed. Type II events often acquired 5' or 3' UTR portions from the locus of integration after the insertion. Type III: novel gene sequence, whose encoded protein has little or no amino acid sequence similarity to that of the retrocopy's parent. Frequently, Type III events include SINEs, LINEs, LTRs etc., as well as unannotated sequences as additional contributors to gene candidates.