mahapeeth-13-Jan-2020

 




Study of meiosis in the dividing pollen mother cells (PMC) onion

Identifying characters of different stages of meiosis:
Prophase:
Pachytene:
i) Nuclear membrane is present. Nucleolus reduced in size.
ii) The pairing is completed and diploid number of chromosome seems to be haploid.
Diplotene:
i) The chromatids of bivalent are distinctly visible.
ii) The length of bivalent is shorter than that of pachytene stage. iii) Chiasmata are visible.
iv) Nucleolus is also present.
Diakinesis:
i) The double chromosomes are appear as ring structure forming loops due to terminalization of chiasmata.
ii) The nucleolus is reduced in size.

               Fig.  Pachytene           Fig. Diplotene  


               Fig. Diakinesis                                                       Fig. Metaphase-I  

Metaphase-I:
i) Nuclear membrane and nucleolus disappear.
ii) Spindle fibres are formed.
iii) The bivalents are arranged at equatorial plate.
Anaphase-I:
i) Two homologous groups of chromosomes being to move towards the opposite pole.
ii) The centromere are towards the pole and the arms towards the equatorial plate.
iii) Each chromosome has two chromatids.

                   Fig. Anaphase-I                                                           Fig. Telophase-I  

Telophase-I:
i) Two groups of diads are reached to their respective poles.
ii) Chromosomes assume regular zigzag shape.
iii) Nuclear membrane reappears.

Prophase-II:
i) Long chromosome threads are prepared.
ii) No single chromosome threads are traceable from one end to another. iii) Nuclear membrane present.

Fig. Interphase Fig. Prophase-II

Metaphase-II:
i) Chromosome groups are arranged at equatorial plate.

Anaphase-II:
i) The daughter chromosomes are started to move towards the opposite poles. ii) The centromeres are splitted lengthwise in the centromere.

                             Fig. Metaphase-II                                          Fig. Anaphase-II  

Telophase-II:
i) The chromosomes were reached at their respective poles.
ii) Each chromosome was single chromatid in value. iii) The chromosome threads are long, elongated.

    Fig. Telophase                                                 Fig. Tetrad  

Tetrad:
i) Four daughter nucleus produce four daughter cells by the two type membrane.
ii) Chromosomes are spread in the nucleus.
iii) Daughter cell contains haploid number of chromosomes.

Young microspore:
i) The young microspores are half moon like
structure.
ii) Nucleus absent. iii) Young nuclear membrane present.

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