Fig. 2

Pseudogene types shown to occur in the human genome. a Unitary pseudogenes are once functional gene sequences that have lost gene function due to the accumulation of mutations over time. b Non-processed pseudogenes are the result of direct duplication of existing genes, after which the duplicated version becomes inactivated due to the accumulation of mutations in sequences essential for gene expression. c Processed pseudogenes are the result of retrotransposition events. In this case, the mature mRNA transcript of a gene is reverse transcribed into a cDNA copy, which is then integrated into the genome of the organism. The site of integration of pseudogenes is random (Adapted from [61])