The
organisms are born without the fusion of the two gametes this phenomenon is
called apomixis. Broadly speaking any type of reproduction that does not
involve sexual fusion may be called apomixis. Winkler who coined the term
apomixis defines it as the substitution of the sexual reproduction by a type of
reproduction which does not involve meiosis and syngamy.
Apomixis is
classified into four categories.
1.
In
the first type generally referred to as non recurrent apomixis. The MMC under
goes meiosis and forms a normal embryo sac. Here the embryo may arise from the
egg cell without syngamy (haploid parthenogenesis) or from some other cells of
the embryo sac (haploid apogamy). The plants produced by such embryo are
haploid and are generally sterile. Maheshwari referred to this type of apomixis
as non recurrent because after one generation the process will stop.
2.
The
second referred to as recurrent type of apomixis. The embryo sac may arise from
MMC but without undergoing reduction division (generative apospory). Sometimes
any cell of the nucellus which is diploid functions as MMC and without
undergoing reduction division develops into embryo sac (somatic apospory) in
this case all the component of the embryo sac are diploid. The embryo might
arise from diploid egg cell without syngamy (diploid parthenogenesis) or from
some other cell of the embryo sac which is also diploid (diploid apogamy).
3.
In
third type embryo arises from nucellus or integument irrespective of the fact
that embryo sac is haploid or diploid. This is called adventive embryony or
sporophytic budding.
4.
In
fourth type the flowers are replaced by bulbils or such other vegetative
propagatives to produce a new individual.
SIGNIFICANCE
1.
It
shortens the time required to produce new individuals.
2.
if
the characters of the individual were to be completely in harmony with the
environmental conditions apomixis assures total transfer of these characters to
the progeny which not the case in the sexual reproducing individuals
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