A sequence of nucleotides in DNA that resembles a gene but has no apparent function. Although most are ‘dead’, many can be transcribed, and some transcripts have gained a role as noncoding RNAs that play a role in regulating functional genes. Pseudogenes are thought to arise by duplication of an existing gene through unequal crossing-over during meiosis, with, e.g., accompanying loss of the promoter or other flanking regions required for transcription. For example, the α‎- and β‎-globin gene clusters in humans contain several pseudogenes. Processed pseudogenes lack promoter and intron sequences and seem to have arisen by reverse transcription of a messenger RNA molecule and insertion of the DNA transcript into the chromosomal DNA at a new location, i.e. retrotransposition.