Pseudogenen

Pseudogenes are DNA sequences that resemble functional genes but are typically nonfunctional due to accumulated mutations that prevent proper transcription or translation. They arise from gene duplication or reverse transcription of mRNA and reinsertion into the genome.

Most pseudogenes are categorized as processed pseudogenes, which originate when mRNA is reverse-transcribed and inserted into the genome, usually lacking introns and often containing a poly-A tail. Non-processed pseudogenes, also called duplicated pseudogenes, arise when gene copies duplicate and subsequently accumulate disabling mutations. A third form, unitary pseudogenes, results when a gene loses function in a lineage without duplication of that gene.

Key features include sequence similarity to a parent gene but disruptions in the open reading frame, premature stop codons, frameshifts, or missing regulatory elements. Processed pseudogenes typically lack introns and may be flanked by target-site duplications. Although many pseudogenes are transcriptionally silent, some are transcribed and can participate in regulatory networks by producing antisense RNA, acting as decoys for microRNAs, or forming novel regulatory elements.

Pseudogenes are common in many genomes, with humans containing thousands of identified pseudogenes. They are useful in studies of genome evolution and gene family history, helping to reconstruct ancestral states and the paths of gene birth and decay. In recent years, research has highlighted potential functional roles for certain pseudogenes, suggesting that the boundary between "pseudogene" and functional gene can be fluid in some contexts.