Apomixis can be defined as a means of asexual reproduction where fertilisation.
Apomixis can be defined as a means of asexual reproduction where fertilisation. The term was first coined by botanist Hans Winkler. The seed of a plant is developed without fertilisation. The Features of Apomixis are:
Apomixis can be classified based on
Apomixis can be observed in hawthorns, shadbush, Sorbus, brambles, and blackberries, meadow grasses, mat grass, hawkweeds, etc.
Apomixis has many applications in the produce sector. Some of them are explained below:
Apomictic plants conserve the genetic structure of their carriers which enables them to maintain heterozygote advantages for many generations. It offers a great advantage in plant breeding where genetic uniformity is maintained for both homo and heterozygosity. The advantages of apomixis are:
The significance or the importance of apomixis in the plant breeding industry is massive. It is a method that develops seeds without fertilization. It can be referred to as a means of asexual reproduction which mimics sexual reproduction. It helps in the production of hybrid seeds and is cost-efficient when it comes to large-scale production. There is an increase in yield as well. Also, since there is no cross-fertilization, apomixis helps in preserving the good characteristics of a crop plant.
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The embryo develops from an egg cell
The embryo originates from synergids or antipodal cells.
It develops from the normal embryo sac cells.
It may be haploid or diploid.
The unreduced embryo sac is derived from a megaspore mother cell by aborted meiotic division or a direct mitotic division. The major types of diplospory apomixis are Taraxacum, Ixeris, and Antennaria. In Taraxacum, the meiotic prophase starts but then the phase is aborted which results in two unreduced dyads one of which gives rise to the embryo sac by mitosis In Ixeris, two further mitotic division of the nuclei give rise to an octa-nucleate embryo sac which follows an equational division following meiotic prophase. In Antennaria, a total of three mitotic divisions form the megagametophyte.
The nuclear cells that give rise to apomictic embryo sacs which are known as aposporos initials are distinct from the ameiotic megasporocyte. The aposporos initial cells may differentiate close to the ameiotic megasporocyte and transform into an apomictic embryo sac. After they differentiate then enter mitotic cell division to produce an embryo sac. Some ovules can contain several embryo sacs and, depending on the plant species, the form of the embryo sac may be – different from that seen in the sexual reproduction process. The initiation apospory embryo sac can occur alongside a sexual one or it can inhibit sexual embryo sac formation.
It is also known as sporophytic apomixis. In this type of apomixis, there may be a megagametophyte in the ovule. However, the embryos do not rise from the cells of the gametophyte. They rise from the cells of nucellus. It can be observed in species of Garcinia, Mangifera indica, etc
It is also called gametophytic apomixis The megagametophyte has the same number of chromosomes as the mother plant. This is due to incomplete meiosis. It generally arises from an archesporial cell or some other part of the nucellus.
The embryo sac consists of haploid cells and the embryo develops from a haploid cell.
The reproduction takes place by apomictic means
The process of reproduction is carried out by both apomictic and sexual means.