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7.2: Modeling the Stages of Meiosis

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    Activity: Modeling the Stages of Meiosis

    Lab Materials

    Materials

    • Chromosome modeling kits
      • Magnetic centromeres (x8)
      • Several red and yellow beads

    Procedure:

    A diploid cell with two homologous pairs of chromosomes (as in the previous modeling exercise) will be modeled as it moves through meiosis. First, you will model meiosis I. Then, you will model meiosis II as described below.

    Modeling Meiosis l:

    1. Build two pairs of replicated homologous chromosomes (i.e., chromosomes that have gone through interphase) using the pop beads. Build one large pair of homologous chromosomes (one red, one yellow) and one smaller pair of homologous chromosomes (one red, one yellow).
    2. Prophase I – First, model synapsis by matching up your pairs of homologous chromosomes to form two tetrads. Next, model crossing-over, which can occur several times along the length of the chromosomes. Use red and yellow beads to represent exchanged segments of chromatids on the inner non-sister chromatids of the tetrad pairs. Place a yellow bead on an inner red (maternal) chromatid to represent DNA exchanged from the paternal chromatid. Place a red bead on an inner yellow (paternal) chromatid to represent DNA from the maternal chromatid. Make a minimum of 1 crossover for each pair of homologous chromosomes.
    3. Metaphase I – Line up the pairs of homologues in the center of your imaginary cell (pairs align independently).
    4. Anaphase I – Separate the pairs of homologous chromosomes by moving them toward opposite poles of the cell.
    5. Telophase I and Cytokinesis I – Completely separate your pairs of homologous chromosomes to represent them moving into two different “cells”. These two cells will enter Meiosis II. Note that each daughter cell has half the number of chromosomes as the parental cell. Thus, the cells have been reduced from diploid (2n) to haploid (n). “n” refers to the number of pairs of chromosomes that are characteristic of a species. Humans have an “n” of 23, so a diploid (2n) human cell has 46 chromosomes, and a haploid (n/1n) human cell has 23 chromosomes.

    Modeling Meiosis II

    1. There is no DNA replication before the second cell division stage of meiosis. The stages of Meiosis II proceed very much like mitosis. The two cells created in Meiosis I will enter into Prophase II. The chromosomes in each cell contain two sister chromatids, which are condensed and distributed throughout the nucleus.
    2. Metaphase II - Line up the individual chromosomes on the equator (middle) of the cell. Sister chromatids remain attached at the centromere during Metaphase ll.
    3. Anaphase II – Pull the magnets (centromeres) apart that attach the sister chromatids to each other to separate them, then move each chromatid toward opposite poles. After separation at the centromere, the chromatids are now called chromosomes.
    4. Telophase II begins when chromosomes reach opposite poles of the cell. Nuclear division happens in telophase. Nuclear envelopes and nucleoli reappear. Condensed chromosomes begin to decondense and uncoil. The formation of separate nuclear envelopes divides the nuclei and marks the end of telophase. Cytokinesis II divides the cytoplasm of each cell into two. A total of four cells are present at the end of Cytokinesis II.
    Follow-Up Questions
    1. How many chromosomes are in the original parent cell? _________
    1. How many chromosomes are in each daughter cell? __________
    1. Are the chromosomes in the daughter cells identical to the chromosomes in the original parent cell? __________________
    1. What is the meaning of the term “diploid”? What abbreviation do we use to represent diploid? Name two diploid cells in humans.
    1. What is the meaning of the term “haploid”? What abbreviation do we use to represent haploid? Name two haploid cells in humans.
    1. In what stage of the cell cycle does DNA replication occur?
    1. What specific feature of cytokinesis can you use to distinguish between plant and animal cell division?

    This page titled 7.2: Modeling the Stages of Meiosis is shared under a CC BY-NC 4.0 license and was authored, remixed, and/or curated by Brad Basehore, Michelle A. Bucks, & Christine M. Mummert via source content that was edited to the style and standards of the LibreTexts platform.