Editing Apomixis (section)

===Incidence in flowering plants===
Apomixis occurs in at least 33 families of flowering plants, and has evolved multiple times from sexual relatives.<ref>{{cite journal|author=Carman, J.G.|year=1997|title=Asynchronous expression of duplicate genes in angiosperms may cause apomixis, bispory, tetraspory, and polyembryony|journal=Biological Journal of the Linnean Society|volume=61|issue=1|pages=51–94|doi=10.1111/j.1095-8312.1997.tb01778.x|doi-access=free}}</ref><ref name=Nygren>{{cite book|author=Nygren, A. |year=1967 |title= Handbuch der Pflanzenphysiologie |chapter= Apomixis in the angiosperms |publisher=Springer-Verlag |location=Berlin|editor= W. Ruhland |pages= 551–596|volume=18}}</ref> Apomictic species or individual plants often have a hybrid origin, and are usually polyploid.<ref name=Nygren/>

In plants with both apomictic and meiotic embryology, the proportion of the different types can differ at different times of year,<ref name=Nogler/> and [[Photoperiodism|photoperiod]] can also change the proportion.<ref name=Nogler/> It appears unlikely that there are any truly completely apomictic plants, as low rates of sexual reproduction have been found in several species that were previously thought to be entirely apomictic.<ref name=Nogler/>

The genetic control of apomixis can involve a single genetic change that affects all the major developmental components, formation of the megagametophyte, parthenogenesis of the egg cell, and endosperm development.<ref name=Koltunow>{{cite journal|author1=Koltunow, A.M. |author2=Johnson, S.D. |author3=Bicknell, R.A. |year=2000|title=Apomixis is not developmentally conserved in related, genetically characterized ''Hieracium'' plants of varying ploidy|journal=Sexual Plant Reproduction|volume=12|issue=5|pages=253–266|doi=10.1007/s004970050193|s2cid=23186733 }}</ref> However, the timing of the various developmental processes is critical to successful development of an apomictic seed, and the timing can be affected by multiple genetic factors.<ref name=Koltunow/>