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Monday, April 22, 2013

Video of Prophase-I of Meiosis Cell Division with Explanation of Different Sub-Phases

BIOLOGY | BOTANY
HSEB Notes on Meiosis Cell Division Prophase-I
CLASS : 11

Meiosis Cell Division 
The process of cell division which takes place in a diploid cell and produces four haploid cell is meiosis cell division i.e. Each cell having half the number of chromosomes as that of parent cell.

Prophase-I 
It is very complex and ling phase. It is further divided into five successive sub phases

Video of Explanation of the Meiosis Cell Division Prophase-I
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  • Different Sub-Phases of Prophase-I
Leptotene 
  • The nucleus increases in size 
  • Chromosomes become slender and separate and distinct threads 
  • Chromosomes contain bead like structures called chromomeres. 
Zygotene 
  • The homologous chromosomes make pair 
Human Chromosomes 
The process of making pair by homologous chromosomes is called synapses.
  • Each pair is called bivalent 
  • The process of synapses is initiated by a kind of attraction force between homologous chromosomes. 
  • The homologous chromosomes can be defined as morphologically and genetically similar one paternal and one maternal chromosome are called homologous chromosomes. 
Pachytene 
  • The homologous pair coiled around each other, Chromosomes replicate, 
  • Chromosomes become shorter and thicker 
  • Each bivalent appears four stranded 
Diplotene 
  • Uncoiling of chromosomes takes place from centromere due to a kind of repulsive force 
  • Some parts however remain still attached at certain points 
  • The attaching points are called chaismata. 
  • At chiasmata chromosomal segments are broken and rejoined cross wise i.e. Exchange of maternal and paternal chromosomal segments. 
  • This phenomenon is called crossing over 
  • Some auther mention the crossing over takes place in pachytene stage. 
Diakinesis 
  • Chiasmata move towards the end of chromosome. This process is called terminalization 
  • The nuclear membrane starts to disappear 
  • Nucleolus also disappear
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