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Apomixis & Polyembryony MCQ - Practice Questions with Answers

Edited By admin | Updated on Sep 18, 2023 18:34 AM | #NEET

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  • Apomixis & Polyembryony is considered one of the most asked concept.

  • 18 Questions around this concept.

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Polyembryony is nothing but 

Concepts Covered - 1

Apomixis & Polyembryony

Apomixis:

  • Apomixis (Gk. apo- without, mixis- mixing) is a mode of reproduction which does not involve the formation of zygote through gametic fusion. 
  • Hence, there is no fertilization involved.
  • In plants apomixis commonly mimics sexual reproduction but produces seeds without fertilisation, e.g., some species of Asteraceae and grasses.
  • It is of following types:
    • Agamospermy
    • Adventive embryony 

Agamospermy:

  • Agamospermy (Gk. a- without, gamos- marriage, sperma- seed) is the formation of seed that has an embryo formed without meiosis and syngamy. 
  • It is of two types, non-recurrent and recurrent.
  • In non-recurrent agamospermy, the embryo is haploid. Therefore, the seed having it is non-viable. 
  • In recurrent agamospermy all the cells of the embryo sac are diploid. 
  • These can be formed:
    • directly from a nucellar cell (apospory
    • Indirectly from diploid megaspore mother cell (diplospory)
  • The diploid egg, as well as other diploid cells of the embryo sac, can grow into normal embryos. 
  • Formation of an embryo directly from a diploid egg without fertilization is called diploid parthenogenesis, e.g., Rubus, Apple, Poa.

Adventive Embryony:

  • An embryo develops directly from a diploid cell other than an egg like that of nucellus and integument, e.g., Citrus, Opuntia. 
  • It gives rise to a con­dition called polyembryony or the phenomenon of having more than one embryo. 
  • There may be more than one egg cell in an embryo sac or more than one embryo sac in an ovule.
  • All the egg cells may get fertilised. 
  • Synergids and antipodal cells may also form embryos. 
  • In gymnosperms, polyembryony can also occur due to cleavage of growing em­bryo. 
  • It is called cleavage polyembryony.
  • The occurrence of polyembryony due to fertilisation of more than one egg is called simple polyembryony. 
  • Formation of extra embryos through sporophytic budding is called adventive polyembryony. 
  • Polyem­bryony is quite common in Onion, Groundnut, Mango, Lemon, Orange.
     

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Apomixis & Polyembryony

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Apomixis & Polyembryony

Biology Textbook for Class XII

Page No. : 39

Line : 1

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