12/21/14

The phases of meiosis



Meiosis refers to the division of gametes. Note: All the things explained below happen after the interphase has been successfully completed.

Meiosis I

Prophase I: 

During prophase I, the chromosomes condense, just like during mitosis. However, there is also a process called synapsis. During synapsis, the chromosomes come together and then they exchange some segments. That gives us more variety, because the chromosomes that are produced are unique. Another thing that happens during prophase I is that the nuclear envelope disappears and the mitotic spindle starts to form (see previous post).



Metaphase I:
As you could predict, the chromosomes meet in the middle during metaphaseI. However, they line up in a different way compared to the way they line up during mitosis. During metaphase I, the homologous chromosomes lie side by side, because the sister chromatids are not going to separate during metaphase I. There are several ways of the arrangement of these chromosomes. The blue chromosome could be on the right side, or on the left side etc. The random arrangement of chromosomes is called independent assortment, and it gives us variety.


Anaphase I:
During anaphase I, the homologous chromosomes are moving apart from each other.


Telophase I:
The telophase I is very similar to the telophase in mitosis. The nuclear envelope reforms, the clevage furrow forms, chromosomes decondense and the organelles migrate to the opposite poles.


 Cytokinesis completes meiosis I. When these two cells above separate, the meiosis I is finished, and the cell is ready to enter meiosis II.

Meiosis II

Prophase II: 
During prophase II, the chromosomes condense, the nuclear envelope fragments and the spindle starts to form.


Metaphase II: 
Metaphase II is just like metaphase in mitosis. The chromosomes meet in the middle, prepared to separate.

Anaphase II: 
During anaphase II, the homologous chromosomes separate. In other words, sister chromatids migrate to the opposite poles of the cell, just like in mitosis.



Telophase II:  
New nuclei form on each side, the clevage furrow forms and the organelles migrate to the opposite poles.

  
Cytokinesis completes meiosis II, and thus the whole process of meiosis. The products of meiosis are therefore four haploid daughter cells, because the DNA replication happens only once.
PLEASE CHECK OUT THE VIDEO I MADE ABOUT MEIOSIS HERE :)

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