Meiosis l Reduction Division
Meiosis is cell division to produce the gametes which have half chromosomes number compared parent cell. Unlike mitosis, it enables genetic variation into gametes by
- Crossing over in Prophase I
- Independent assortment in Metaphase I
It involves 2 divisions:
- Meiosis I – reduction division
- Meiosis II – as mitosis
Meiosis
Meiosis I
Prophase I
Early Prophase I
- Centrioles replicate and move to opposite poles of cell.
- Chromosomes condense and become visible.
- Homologous chromosomes pair up forming bivalents.
Late Prophase I
- Nuclear envelope break up.
- Nucleolus disappear.
- Bivalents show crossing over. One or more chiasma may occur.
- Spindle is formed in the end of prophase.
Metaphase I
Metaphase I
- Bivalents are lined up across the equatorial line, attached by centromeres
Anaphase I
Anaphase I
- Homologous chromosomes move to opposite poles of the spindle where centromeres move first and pulled by microtubules.
- Centromeres do not divide.
Telophase I and Cytokinesis
Telophase I & cytokinesis
- Reform nuclear envelope and nucleolus.
- Spindle remains.
- Each daughter cell has half number chromosomes compared parent cell.
Meiosis II
Prophase II
Prophase II
- Nuclear envelope and nucleolus disperse.
- Centrioles replicate and move to opposite poles of cell.
Metaphase II
Metaphase II
- Chromosomes line up separately across equator line of spindle
Anaphase II
Anaphase II
- Centromeres divide and chromatids are pulled to opposite poles by spindle microtubules.
Telophase II and Cytokinesis
Telophase II & cytokinesis
- Nuclear envelope and nucleolus are reformed.
- Four haploid daughter cells are formed.
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