Tuesday, January 25, 2011

Meiosis _ Prophase ends

Meiosis I
Meiosis II

Meiosis I

1) Prophase I


    a)Leptotene
    b)Zygotene
    c)Pachytene
    d)Diplotene
    e)Diakinesis


    a)Leptotene - Chromosomes are stretched and thread-like
    b)Zygotene - Chromosomes become shorter and thicker. Homologous chromosomes pair up.

Synapsis 
Pairing of two homologous chromosomes in meiosis.Gene to gene pairing occur.Pairing is accompanied by the appearance of Synaptonemal Complex (SC) which is an ultra structural cell component. Tripartite ribbon like structure associated with each paired homologue. Help homologous chromosomes to correctly pair up.

    c)Pachytene - chromosomes become thicker and more clear.Two  chromatids are visible.  
According to chromosomes - bivalent chromosomes
According to chromatids - tetrad chromatids 
Crossing over occurs

Crossing over
Exchange of genetic material between two homologous chromosomes. Possible due to synapsis.

    d)Diplotene - Paired chromosomes starts to repel each other. bivalents are still held together fro points of exchange. Repulsion more visible near centromere.
     e)Diakinesis - Chromosomes show the maximum amount of coiling. The most favorable stage to count chromosomes. Since bi-valents are counted the haploid number is obtained.

First meiotic prophase ends with the diaapearance of the nucleoli and nuclear membrane.

6 comments:

  1. is this related to the cell biology course unit of the uni?

    in our days, we were only taught about molecular cell biology of the cell membrane for 15 lectures

    ReplyDelete
  2. No no
    It's not cell biology
    It's the genetics course
    :D

    ReplyDelete
  3. it is related to meiotic cell division

    ReplyDelete
  4. it is related to meiotic cell division

    ReplyDelete
  5. it is related to Cytogenetics
    I knew about it in school

    ReplyDelete
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