Biology today

Fig.:Meiosis inLilium grandiflorum(Lily)

Interphase Leptotene Zygotene Pachytene

Diplotene Diakinesis Metaphase I (side) Metaphase I (polar)

Anaphase-I Telophase-I Prophase-II Metaphase-II

Anaphase-II Telophase-II Tetrad Microspore

Table : Formulae chart

1. Number of mitotic divisions for
   the formation of n number of
   cells.
   example : for getting 100 cells 99
   mitotic divisions are required.

n – 1

2. Number of generations (n) of
   mitosis for producing ‘x’ cells

x = 2n

3. Number of meiosis for the
   formation of ‘n’ seeds/grains/
   fruits

n + n

4

Significance of meioSiS

• Meiosis is essential for formation of gametes and
  maintenance of chromosome number in sexually
  reproducing organisms. Gametes are produced by
  meiosis and have half the number of chromosomes.
  It is essential to maintain species specific number
  of chromosomes. Since the chromosome number
  becomes double after fertilisation.
  
  
  • In meiosis paternal and maternal chromosomes assort
    independently that causes reshuffling of chromosomes
    and the traits controlled by them.
  
  
  • Crossing over results in new combination of traits and
    produce variations. Variations serve as raw material for
    evolution of new species.
  
  
  • Details of meiosis are essentially similar in the majority
    of organisms showing their basic similarity and
    relationship.
  
  
  
  

eVentS common in mitoSiS anD

meioSiS

• Similar types of changes in the nucleus and cytoplasm
  during both divisions.


• The stages of prophase, metaphase, anaphase, and
  telophase are common in both cell divisions.


• formation of the asters and spindle during meiosis, as
  in mitosis.


• The condensation of chromosomes during both
  divisions.


• Structure and function of the kinetochore are same in
  both divisions.