Pseudogenes

Pseudogenes are segments of DNA that are related to real genes. Pseudogenes have lost at least some functionality, relative to the complete gene, in cellular gene expression or protein-coding ability. Pseudogenes often result from the accumulation of multiple mutations within a gene whose product is not required for the survival of the organism, but can also be caused by genomic copy number variation (CNV) where segments of 1+ kb are duplicated or deleted. Although not fully functional, pseudogenes may be functional, similar to other kinds of noncoding DNA, which can perform regulatory functions. The "pseudo" in "pseudogene" implies a variation in sequence relative to the parent coding gene, but does not necessarily indicate pseudo-function. Despite being non-coding, many pseudogenes have important roles in normal physiology and abnormal pathology.

Although some pseudogenes do not have introns or promoters (such pseudogenes are copied from messenger RNA and incorporated into the chromosome, and are called "processed pseudogenes"), others have some gene-like features such as promoters, CpG islands, and splice sites. They are different from normal genes due to either a lack of protein-coding ability resulting from a variety of disabling mutations (e.g. premature stop codons or frameshifts), a lack of transcription, or their inability to encode RNA (such as with ribosomal RNA pseudogenes). The term "pseudogene" was coined in 1977 by Jacq et al.

Because pseudogenes were initially thought of as the last stop for genomic material that could be removed from the genome, they were often labeled as junk DNA. Nonetheless, pseudogenes contain biological and evolutionary histories within their sequences. This is due to a pseudogene's shared ancestry with a functional gene: in the same way that Darwin thought of two species as possibly having a shared common ancestry followed by millions of years of evolutionary divergence, a pseudogene and its associated functional gene also share a common ancestor and have diverged as separate genetic entities over millions of years.

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