Editing Human genome (section)

=== Pseudogenes ===
{{Main|Pseudogene}}

Pseudogenes are inactive copies of protein-coding genes, often generated by [[gene duplication]], that have become nonfunctional through the accumulation of inactivating mutations. The number of pseudogenes in the human genome is on the order of 13,000,<ref name="Pei2012">{{cite journal | vauthors = Pei B, Sisu C, Frankish A, Howald C, Habegger L, Mu XJ, Harte R, Balasubramanian S, Tanzer A, Diekhans M, Reymond A, Hubbard TJ, Harrow J, Gerstein MB | title = The GENCODE pseudogene resource | journal = Genome Biology | volume = 13 | issue = 9 | pages = R51 | year = 2012 | pmid = 22951037 | pmc = 3491395 | doi = 10.1186/gb-2012-13-9-r51 | doi-access = free }}</ref> and in some chromosomes is nearly the same as the number of functional protein-coding genes. Gene duplication is a major mechanism through which new genetic material is generated during [[molecular evolution]].

For example, the [[olfactory receptor]] gene family is one of the best-documented examples of pseudogenes in the human genome. More than 60 percent of the genes in this family are non-functional pseudogenes in humans. By comparison, only 20 percent of genes in the mouse olfactory receptor gene family are pseudogenes. Research suggests that this is a species-specific characteristic, as the most closely related primates all have proportionally fewer pseudogenes. This genetic discovery helps to explain the less acute sense of smell in humans relative to other mammals.<ref>{{cite journal | vauthors = Gilad Y, Man O, Pääbo S, Lancet D | title = Human specific loss of olfactory receptor genes | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 100 | issue = 6 | pages = 3324–3327 | date = Mar 2003 | pmid = 12612342 | pmc = 152291 | doi = 10.1073/pnas.0535697100 | bibcode = 2003PNAS..100.3324G | doi-access = free }}</ref>