Pseudogenes are similar to normal genes (they have promoters, CpGs and splice sites, although some do not contain intrones or promotres, because some were generated from mRNA) but are not functional. They lost their ability to encode proteins and are no longer expressed in cells. Due to loss of function of pseudogenes, they are often referrred to as "junk DNA". Therefore pseudogenes are homologuous to a known gene, but are non-functional.
Types of pseudogenes:
- processed (retrotransposed) pseudogenes: an mRNA transcript is reverse-transcribed back to DNA and inserted into a chromosome. These genes usually contain a poly-A tail and they lack intrones (which have been spliced out) and upstream promotores of normal genes
- non-processed (duplicated) pseudogenes: created by gene duplication and an additional mutation, which renders them non-functional. These pseudogenes have same characteristics as their functional homologues, including intrones and promoter sequences.
- disabled genes (unitary) pseudogenes: generated by a fixed mutation in a population, which makes the gene non-functional
Comprehensive database of identified pseudogenes, utilities used to find pseudogenes, various publication data sets and a pseudogene knowledgebase