Name: ____________________________
Meiosis is the process of two successive nuclear divisions to create four haploid cells. Meiosis I is the
first division where the homologous chromosomes are separated and the cell is reduced from diploid to
haploid. Meiosis II is the division where the sister chromatids are separated resulting in four new
haploid gametes.
Pre-Lab
1. Diagram a tetrad below. Label the homologous chromosomes, sister chromatids and the
centromeres. Define these terms below.
Homologous chromosome-
Sister chromatid-
Centromere-
2. In addition to reducing the chromosome number in half, what is the other primary purpose of
meiosis? What two events accomplish this goal and in what stages are they found?
Modeling the Phases
In this exercise you will simulate meiosis using the chromosome modeling kits. You should have
available two strands of yellow beads and two strands of red beads, along with four magnetic links. A
homologous pair of chromosomes is represented by one strand of each color, each color representing a
different parent. The extra beads are to model DNA replication. You may use two different desks to
model different cells that will be created. You will also have yarn to model the cell’s nucleus and spindle
fibers.
1. Utilize the following table to model a normal meiosis with your partner then answer the
following questions.
Modeling
Phase
DNA Replication
Model the replication of DNA.
Prophase I
Create tetrads (XX) by pairing homologous chromosomes, the creation of the mitotic
spindle and the destruction of the nucleus. Model crossing over by popping off
beads from one chromosome and exchanging them with another of a different color
at the same location.
Metaphase I
Line up your tetrads along the metaphase plate. Model independent assortment by
simulating all of the possible orientations of the homologues; decide one to use for
the following stages.
Anaphase I
Separate the homologous chromosomes by moving them to opposite ends of the cell.
Telophase I
Model the reappearance of the nucleus. You should have two chromosomes in each of
your two nuclei.
Cytokinesis I
Model the creation of two daughter cells.
Prophase II
Check to make sure that each of your two cells contains two chromosomes made up of
sister chromatids.
Metaphase II
Line your chromosomes up along the middle of each of your cells.
Anaphase II
Separate your sister chromatids. Move one sister chromatid from each chromosome to
opposite sides of your cell.
Telophase II
Model the reappearance of the nucleus. You should now have four nuclei, with two
single chromatids in each of the cells.
Cytokinesis II
Divide your cell membranes so that you have four daughter cells.
2. Describe at least three differences between mitosis and meiosis.
3. How are meiosis I and meiosis II different? Explain.
4. Why is meiosis important for sexual reproduction? Explain.
Scenario Modeling
Model the process of meiosis using the table on page two again, except this time model the process in
the context given in number 5. Then, answer the following questions.
5. A person with Down syndrome has an extra 21st chromosome. Model the process of meiosis
that would be the precursor to a person having an extra chromosome.Show me (the teacher)
the critical step when you arrive at it; call me over.
6. This type of error is called nondisjunction. What types of consequences do you think are
associated with this type of meiotic error?
Analysis Questions
1. Visually, what is the major difference between prophase I and prophase II?
2. What is crossing over? When does it occur during meiosis? How did you model this element of
meiosis?
3. Visually, what is the major difference between metaphase I and metaphase II?
4. What is independent assortment? When does it occur during meiosis? How did you model this
element of meiosis?
5. Which part of meiosis, meiosis I or meiosis II, is responsible for halving the number of
chromosomes?