Editing Molecular evolution (section)

==Origins of new genes==

New [[gene]]s arise from several different genetic mechanisms including [[gene duplication]], [[de novo gene birth|''de novo'' gene birth]], [[Gene duplication#Retrotransposition|retrotransposition]], [[chimeric gene]] formation, recruitment of non-coding sequence into an existing gene, and gene truncation.

[[Gene duplication]] initially leads to redundancy. However, duplicated gene sequences can mutate to develop [[Neofunctionalization|new functions]] or [[Subfunctionalization|specialize]] so that the new gene performs a subset of the original ancestral functions. [[Retrotransposition]] duplicates genes by copying [[mRNA]] to DNA and inserting it into the genome.  Retrogenes generally insert into new genomic locations, lack [[intron]]s, and sometimes develop new expression patterns and functions.

[[Chimeric gene]]s form when duplication, deletion, or incomplete retrotransposition combines portions of two different coding sequences to produce a novel gene sequence.  Chimeras often cause regulatory changes and can shuffle protein domains to produce novel adaptive functions.

[[De novo gene birth|''De novo'' gene birth]] can give rise to protein-coding genes and non-coding genes from previously non-functional DNA.<ref>{{cite journal | vauthors = McLysaght A, Guerzoni D | title = New genes from non-coding sequence: the role of de novo protein-coding genes in eukaryotic evolutionary innovation | journal = Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences | volume = 370 | issue = 1678 | pages = 20140332 | date = September 2015 | pmid = 26323763 | pmc = 4571571 | doi = 10.1098/rstb.2014.0332 }}</ref>  For instance, Levine and colleagues reported the origin of five new genes in the ''D. melanogaster'' genome.<ref name="j3" /><ref name="j4" /> Similar ''de novo'' origin of genes has also been shown in other organisms such as yeast,<ref name="j5" /> rice<ref name="j6" /> and humans.<ref name="j7" /> ''De novo'' genes may evolve from spurious transcripts that are already expressed at low levels.<ref>{{cite journal | vauthors = Wilson BA, Masel J | title = Putatively noncoding transcripts show extensive association with ribosomes | journal = Genome Biology and Evolution | volume = 3 | pages = 1245–1252 | year = 2011 | pmid = 21948395 | pmc = 3209793 | doi = 10.1093/gbe/evr099 }}</ref>