IB DP Biology: SL复习笔记3.2.5 Skills: Meiosis

Drawing the Stages of Meiosis

  • Cells undergoing meiosis can be observed and photographed using specialized microscopes
  • The different stages of meiosis have distinctive characteristics meaning they can be identified from photomicrographs
  • Being able to identify the stages of meiosis from photomicrographs and diagrams is an important skill for a biologist

Step 1: Identifying if meiosis I or meiosis II is occurring

  • 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 also help identify whether meiosis I or II is occurring
    • If there are two new cells forming it is meiosis I but if there are four new cells forming it is meiosis II

Identifying which stage of meiosis I is occurring

  • Prophase I: Homologous pairs of chromosomes are visible in diploid cell (2n). Crossing over occurs
  • Metaphase I: Spindle fibres pull homologous pairs so they are lined up side by side along the equator of the cell. Orientation of homologous chromosomes is random
  • 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 the cell membrane is pinching inwards to form two cells with haploid chromosome numbers (n)


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

Identifying which stage of meiosis II is occurring

  • Prophase II: Single whole chromosomes are visible in haploid cells
  • Metaphase II: Single whole chromosomes are lined up along the equator of the cell in a single file
  • 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


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

Drawing the stages of meiosis

  • The distinguishing features mentioned above can also be used by biologists to draw scientific diagrams of meiosis I and meiosis II
  • The conventions for drawing are:
    • The drawing must have a title
    • A sharp HB pencil should be used (and a good eraser!)
    • Drawings should be on plain white paper
    • Lines should be clear, single lines (no thick shading)
    • No shading
    • The drawing should take up as much of the space on the page as possible
    • Well-defined structures should be drawn
    • The drawing should be made with proper proportions
    • Label lines should not cross or have arrowheads and should connect directly to the part of the drawing being labelled


Drawing the different stages or phases of meiosis

Exam Tip

For metaphase remember M for the middle of the 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.When drawing the stages of meiosis you do not have to show crossing over occurring.