Meiosis

Meiosis is a cellular division for gametes that takes place in the gonads (ovaries and testes).The result of meiosis is four non identical daughter cells that are haploid. The process of meiosis is pivotal in establishing variation. Prior to enter meiosis the cells will have undergone interphase (G1, S and G2 stages)

Stages of meiosis

Prophase 1

  • The nuclear membrane disappears.
  • Chromosomes condense, making them visible as individual chromosomes.
  • Crossing over occurs.

Metaphase 1

  • Homologous pairs line up along the equator cell side by side forming a tetrad. This is different to the alignment taken in metaphase of mitosis.

Anaphase 1

  • Each homologous pair undergoes disjunction as double stranded chromosomes migrate to their respective poles.
  • Unlike anaphase in mitosis there is no splitting of centromeres.
  • The spindle fibers disappear.

Telophase 1

  • Spindle breaks down.
  • Nuclear membrane begins to reform

Cytokinesis occurs after meiosis one.

The cells undergo a resting phase, no DNA synthesis occurs.

Prophase 2

  • In both cells the nuclear envelope breaks down.
  • Spindle fibres form.
  • Chromosomes condense and become visible.

Metaphase 2

  • In both cells chromosomes align on the equator of the cell, one above another and not in pairs unlike in meiosis 1.

Anaphase 2

  • Chromosomes separate at the centromere undergoing disjunction and migrate to their respective poles
  • Spindle fibers disappear.

Telophase 2

  • Spindle breaks down.
  • Nuclear membrane begins to reform.

Cytokinesis divides the cytoplasm resulting in 4 haploid daughter cells that are non-identical to the parental cells.

stages2

Click to enlarge1

See also


  1. http://www.phschool.com/science/biology_place/labbench/lab3/concepts2.html1