Figure 1.

The generation of a retrogene. Infrequently, a spliced, capped and polyadenylated cellular mRNA molecule is reverse transcribed (RT) into cDNA and integrated by retrotransposition into the genome in an intergenic region, creating an intronless copy of the gene, a retrocopy (blue), lacking its own promoter and regulatory elements. Over time, the insertion of a transposable element (TE) upstream of the retrocopy can provide both a promoter and, by the process of exonization, a new 5' UTR exon (yellow), such that, after splicing, the transcript yields a functional mRNA. The new functional gene is termed a retrogene and if useful to the organism, will be maintained in the genome.