Gametophytic apomixis: elements and genetic regulation

Gametophytic apomixis implies formation of unreduced embryo-sacs and capacity of their egg cells for parthenogenetic development. Each of these processes, as well as their union to give matromorphous offspring, are known from several species with sexual reproduction. A comparative survey is given of meiotic modifications, occurrence of apospory, female and male parthenogenesis and aberrant endosperm formation in sexual and apomictic species. Knowledge and models concerning the genetic basis of apomictic reproduction are summarized, as well as effects upon apomixis of changes of chromosome number and of hybridization. In the author's opinion, the constituents or elements of apomixis are — with the possible exception of apospory—to a large extent quantitative traits under polygenic control.