Editing Selfish genetic element (section)

===Early observations ===
Observations of what is now referred to as selfish genetic elements go back to the early days in the [[history of genetics]]. Already in 1928, Russian geneticist [[Sergey Gershenson]] reported the discovery of a driving [[X chromosome]] in ''Drosophila obscura''.<ref name=":5">{{cite journal | vauthors = Gershenson S | title = A New Sex-Ratio Abnormality in DROSOPHILA OBSCURA | journal = Genetics | volume = 13 | issue = 6 | pages = 488–507 | date = November 1928 | doi = 10.1093/genetics/13.6.488 | pmid = 17246563 | pmc = 1200995 }}</ref> Crucially, he noted that the resulting female-biased sex ratio may drive a population extinct (see [[#Species extinction|Species extinction]]). The earliest clear statement of how chromosomes may spread in a population not because of their positive fitness effects on the individual organism, but because of their own "parasitic" nature came from the Swedish botanist and cytogeneticist [[Gunnar Östergren]] in 1945.<ref name=":6">{{cite journal | vauthors = Östergren G | title = Parasitic nature of extra fragment chromosomes. | journal = Botaniska Notiser | date = 1945 | volume = 2 | pages = 157–163 }}</ref> Discussing [[B chromosome]]s in plants he wrote:<ref name=":6" />

<blockquote>In many cases these chromosomes have no useful function at all to the species carrying them, but that they often lead an exclusively parasitic existence ... [B chromosomes] need not be useful for the plants. They need only be useful to themselves.</blockquote>

Around the same time, several other examples of selfish genetic elements were reported. For example, the American maize geneticist [[Marcus Morton Rhoades|Marcus Rhoades]] described how chromosomal knobs led to female [[meiotic drive]] in maize.<ref>{{cite journal | vauthors = Rhoades MM | title = Preferential Segregation in Maize | journal = Genetics | volume = 27 | issue = 4 | pages = 395–407 | date = July 1942 | doi = 10.1093/genetics/27.4.395 | pmid = 17247049 | pmc = 1209167 }}</ref> Similarly, this was also when it was first suggested that an [[intragenomic conflict]] between [[uniparental inheritance|uniparentally inherited]] mitochondrial genes and biparentally inherited nuclear genes could lead to [[cytoplasmic male sterility]] in plants.<ref name=":7">{{cite journal | vauthors = Lewis D | title = Male sterility in natural populations of hermaphrodite plants the equilibrium between females and hermaphrodites to be expected with different types of inheritance. | journal = New Phytologist | date = April 1941 | volume = 40 | issue = 1 | pages = 56–63 | doi = 10.1111/j.1469-8137.1941.tb07028.x | doi-access = free }}</ref> Then, in the early 1950s, [[Barbara McClintock]] published a series of papers describing the existence of [[transposable element]]s, which are now recognized to be among the most successful selfish genetic elements.<ref name=":8">{{cite journal | vauthors = McClintock B | title = The origin and behavior of mutable loci in maize | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 36 | issue = 6 | pages = 344–55 | date = June 1950 | pmid = 15430309 | pmc = 1063197 | doi = 10.1073/pnas.36.6.344 | bibcode = 1950PNAS...36..344M | doi-access = free }}</ref> The discovery of transposable elements led to her being awarded the [[Nobel Prize in Physiology or Medicine|Nobel Prize in Medicine or Physiology in 1983]].