CIE A Level Biology复习笔记16.1.4 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

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

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