Apomixis, derived from two Greek words “APO” (away from) and “mixed” ( the act of mixing or mingling). It refers to the occurrence of an asexual reproductive process in the place of normal sexual processes involving reduction division and fertilization. Apomixis can be best described as the reference to the asexual process.
During sexual reproduction, developmental steps occurring inside the ovule produce the female gametophyte (embryo sac) and following a double fertilization event give rise to embryo and endosperm structures.
Apomixis is widely distributed among higher plants. More than 300 species belonging to 35 families are apomictic. It is most common in Gramineae, Compositae, Rosaceae, and Rutaceae. Among the major cereals maize, wheat, and pearl millet have apomictic relatives.
Types of Apomixis
Three types of apomixis are generally recognized – diplospory, apospory and adventitious embryony. These apomictic processes are depicted compared to sexual processes in the formation of a common Polygonum-type embryo sac.
In the Taraxacumtype, meiotic prophase is initiated but then the process is aborted resulting in two unreduced dyads one of which gives rise to the embryo sac by mitotic division.
In the Ixeris type, two further mitotic divisions of the nuclei to give rise to an eight-nucleate embryo sac follow equational division following meiotic prophase. The Taraxacum and Ixeris types are known as meiotic diplospory because they involve modifications of meiosis.
In general, fertilization in the adjoining sexual embryo sac and subsequent endosperm formation is necessary to form viable seeds. The developing embryos closest to the embryo sac grow towards it, presumably to obtain nutrient and other developmental signals from the embryo sac.
There are some few further types of apomixis which are discussed in brief below.
Recurrent and Non-recurrent Apomixis
Benefits of Apomixis
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