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BIOLOGY in Marathi

Understanding is IMPORTANT.......

Prof. Deshmukh A. B.'s Biology Class

https://www.onlinesciencestudy.com

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1. REPRODUCTION IN LOWER & HIGHER PLANTS

-CREATED BY-

PROF. DESHMUKH A. B.

ASST. TEACHER

SEC. & HIGHER SEC. SCHOOL, SHENDI (BHANDARDARA DAM),

TAL. – AKOLE, DIST. - AHMEDNAGAR

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1.13 Apomixis (Away from mixing):

  • It is phenomenon of formation of embryo(s) through asexual method of reproduction without formation of gametes and the act of fertilization.

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  • Alternatively, it is unusual sexual reproduction where there is no meiosis and syngamy.

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  • Embryo develops in the ovule and ovule develops to form seed .

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(No Meiosis)

MMC (2n)

Embryo sac (2n)

Egg (2n)

+

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Megaspore mother cell (MMC) (2n)

Nucellus

Meiosis

Mitosis

Functional Megaspore

(n)

Degenerating Megaspores (n)

Double Feritlization

Antipodal Cells (n)

Polar Nuclei (2n)

Egg cell (n)

Seed Coat

Synergids (n)

Endosperm

Embryo

Sexual Seed Formation

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  • In apomixis,
    • when a gametophyte organ or cell produces embryo like structure without fertilization, it is termed as apogamy.

    • similarly, when diploid sporophyte cell produces a diploid gametophyte without undergoing meiosis is called apospory.

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    • e.g. Orange, Mango.

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(No Meiosis)

(No Fertilization)

MMC (2n)

Embryo sac (2n)

Embryo (2n)

(Mega gametophyte)

(No Meiosis)

(No Fertilization)

Nucellar cell (2n)

Embryo sac (2n)

Embryo (2n)

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  • The main categories of apomixis are:

a. Recurrent apomixis

b. Non-recurrent apomixis

c. Adventive Embryony

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a. Recurrent apomixis :

  • In this type, the embryo sac generally rise either from an archesporial cell or from some other part of the nucellus.

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Nucellus

Archesporial cell (2n)

Mitosis

Mitosis

Embryo (2n) develops

Without

Fertilization

Any nucellar cell (2n)

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Embryo Sac

(2n)

© Prof. Deshmukh A. B’s Biology Class

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  • In diplospory, the unreduced embryo sac is derived from the diploid megaspore mother cell

e.g., Taraxacum.

  • In apospory, the nucellar cells (2n) give rise to apomictic embryo sac.

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(Mitosis)

(No Fertilization)

MMC (2n)

Embryo sac (2n)

Embryo (2n)

(Mitosis)

(No Fertilization)

Nucellar cell (2n)

Embryo sac (2n)

Embryo (2n)

(Apomictic)

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b. Non-recurrent apomixis :

  • In this type, megaspore mother cell undergoes usual meiotic division and a haploid embryo sac is formed.
  • Here, the embryo arises
    • either from the egg by parthenogenesis
    • or from some other haploid cells of gametophyte through apogamy.
  • Plants produced by this method are generally sterile and do not reproduce sexually,

e.g., Nicotiana.

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Megaspore mother cell (MMC) (2n)

Nucellus

Meiosis

Functional Megaspore

(n)

Degenerating Megaspores (n)

Antipodal Cells (n)

Polar Nuclei (2n)

Egg cell (n)

Synergids (n)

Embryo Sac (n)

Embryo

(n)

From Egg (n) by Parthenogenesis

From any gametophyte cell (n)

Through Apogamy

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c. Adventive Embryony :

  • In this type, embryos may develop from

somatic nucellus

or

integuments along with normal zygotic embryo.

  • It is common in Mango, Orange, Lemon, etc.
  • It gives rise to a condition called polyembryony.
  • Genetically identical plants can be produced effectively and rapidly by apomixis.

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Megaspore mother cell (MMC) (2n)

Nucellus

Meiosis

Functional Megaspore

(n)

Degenerating Megaspores (n)

Antipodal Cells (n)

Polar Nuclei (2n)

Egg cell (n)

Synergids (n)

Embryo Sac (n)

Zygotic

Embryo

(2n)

Embryo from Somatic nucellar cell or Integument

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