Meiosis l Reduction Division

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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:

  1. Meiosis I – reduction division
  2. Meiosis II – as mitosis
meiosis, cell division

Meiosis

Meiosis I

Prophase 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, meiosis

Metaphase I

Metaphase I

  • Bivalents are lined up across the equatorial line, attached by centromeres
Anaphase I, meiosis

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, meiosis

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

Prophase II

  • Nuclear envelope and nucleolus disperse.
  • Centrioles replicate and move to opposite poles of cell.
Metaphase II

Metaphase II

Metaphase II

  • Chromosomes line up separately across equator line of spindle
Anaphase II, meiosis

Anaphase II

Anaphase II

  • Centromeres divide and chromatids are pulled to opposite poles by spindle microtubules.
Telophase II

Telophase II and Cytokinesis

Telophase II & cytokinesis

  • Nuclear envelope and nucleolus are reformed.
  • Four haploid daughter cells are formed.

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