IB Biology SL

Revision Notes

3.2.5 Skills: Meiosis

Identifying the Stages of Meiosis

  • Cells undergoing meiosis can be observed and photographed using specialised microscopes
  • The different stages of meiosis have distinctive characteristics meaning they can be identified from photomicrographs or diagrams

Meiosis I or Meiosis II

  • Homologous chromosomes pair up side by side in meiosis I only
  • This means if there are pairs of chromosomes in a diagram or photomicrograph meiosis I must be occurring
  • The number of cells forming can help distinguish between meiosis I and II
  • If there are two new cells forming it is meiosis I but if there are four new cells forming it is meiosis II

The distinguishing features at each stage of Meiosis I

  • Prophase I: Homologous pairs of chromosomes are visible
  • Metaphase I: Homologous pairs are lined up side by side along the equator of spindle
  • Anaphase I: Whole chromosomes are being pulled to opposite poles with centromeres intact
  • Telophase I: There are 2 groups of condensed chromosomes around which nuclei membranes are forming
  • Cytokinesis: Cytoplasm is dividing and cell membrane is pinching inwards to form two cells

The distinguishing features at each stage of Meiosis II

  • Prophase II: Single whole chromosomes are visible
  • Metaphase II: Single whole chromosomes are lined up along the equator of the spindle in single file (at 90 degree angle to the old spindle)
  • Anaphase II: Centromeres divide and chromatids are being pulled to opposite poles
  • Telophase II: Nuclei are forming around the 4 groups of condensed chromosomes
  • Cytokinesis: Cytoplasm is dividing and four haploid cells are forming

Identifying the stages of meiosis table

Identifying the Stages of Meiosis Table, downloadable AS & A Level Biology revision notes

Photomicrograph showing stages of Meiosis I, downloadable AS & A Level Biology revision notes

Prophase I, Metaphase I , Anaphase I and Telophase I as seen in photomicrographs

Photomicrograph showing stages of Meiosis II, downloadable AS & A Level Biology revision notes

Prophase II, Metaphase II , Anaphase II and Telophase II as seen in photomicrographs

Exam Tip

For metaphase remember M for the middle of the spindle and cell which is where the chromosomes will be lined up.

For anaphase remember A for away from the middle to the poles, which is where the chromosomes / chromatids are being pulled.

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