Pseudogenes are defective copies of functional genes. These may be partial or complete duplicates derived from polypeptide-encoding genes or RNA genes. The DNA sequence of a pseudogene is characteristically very similar to its functional counterpart, but contains variant mutations that render the gene inactive. The functional polypeptide-encoding gene contains an open reading frame, a long stretch of nucleotides that are transcribed and subsequently translated into a series of amino acids uninterrupted by stop codons. In contrast, pseudogenes derived from polypeptide sequences generally are punctuated with stop codons, effectively rendering them incapable of producing a functional protein.

Pseudogenes may also contain frameshift mutations, yielding a change in the reading frame. Additionally, there may be mutations that inactivate regulatory elements or intron-splicing sites. In either case, the duplicated gene may be rendered nonfunctional. Genes and pseudogenes derived from the duplication of an ancestral gene are said to be paralogous.

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