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What is Meiosis ? Write an Account of the Process of 

 Meiotic Division. 



A special kind of nuclear division, a form of mitosis, 

 known as " Meiotic or Reduction Division," which occurs 

 only in the maturation of the gametes or sex cells ; and 

 in which the number of the chromosomes is reduced to 

 half the normal number present in the nuclei of the somatic 

 or body cells of the same animal. In reduction division 

 there is a prolonged skein (spireme) stage. The chromatin 

 threads unite in pairs (syndesis). There may be contraction 

 and a clumping together (synizesis) which may be followed 

 by loosening out again and further synizesis. 



By shortening and thickening the paired threads become 

 segmented and isolated as bivalents, twin-bodies or gemini. 

 They may be incompletely separated and widened out 

 in a sort of ring form, or separate rod-like segments in 

 close association. 



The bivalent chromosomes are then scattered further 

 apart, and this is the stage termed diakinesis. The nuclear 

 membrane disappears, the spindle is formed, and to its 

 fibres the bivalent chromosomes become attached in the 

 equatorial position. The bivalents are divided across 

 the point of junction of the constituent chromosomes, 

 and each of these passes towards the poles. Each separate 

 constituent often has a ^ -=* form, the limbs of which may 

 be lying parallel, as it nears the pole, thus giving it a 

 double appearance. Because of that peculiarity of form, 

 this first meiotic division is often termed heterotype. The 

 formation of the daughter-nuclei is completed as in ordinary 

 mitotic division and the two resulting daughter cells are 

 separated. It is plain, therefore, that while the cells of the 

 earlier generations have 2n chromosomes, the cells in which 

 the heterotype division takes place have n bivalents or 

 gemini, and the resulting daughter cells n single or univalent 

 chromosomes. 



The second division (of the nuclei of the two daughter 

 cells) which promptly follows is called homotype, because 

 it presents no peculiarities and in process resembles ordin- 



