Download Lab 11H - Mitosis and Meiosis_procedure only

 Lab #11: Mitosis & Meiosis Simulation
Objectives
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Understand the cell cycle and process of cell division
Demonstrate mitosis and meiosis using pop bead models
Simulate segregation of alleles, independent assortment, and crossing over during cell
division
Materials
MATERIALS NEEDED PER GROUP
Did you know? 40 Red pop beads
40 Yellow pop beads
2 Red centromeres
2 Yellow centromeres
8 Plastic tubular centrioles
In the time it takes to read this sentence, approximately 50,000 cells will die and be replaced with new ones. Procedure
Activity #1: Mitosis
Use Analysis Sheet #1: Mitosis to diagram each stage of mitosis as you simulate in this exercise.
A. Interphase
What happens:
After cell division takes place, the cell enters the longest stage of the cell cycle. This is called
interphase. During this stage, the cell is preparing for the next division. Distinct chromosomes
are not visible. DNA exists in an uncoiled state and the chromosome material appears as granular
matter, called chromatin, within the nucleus.
To simulate:
1. Construct two strands of seven red pop beads and attach them to a red centromere. Repeat
with two strands of seven yellow pop beads and a yellow centromere. These will represent a
homologous pair of chromosomes.
Adapted from WARDS Mitosis & Meiosis Simulation Laboratory. 2. Picture an imaginary boundary in the center of your desk. This boundary will represent the
nuclear membrane. Place the chromosomes in the center of the imaginary nucleus.
3. DNA replication occurs, producing a duplicate of each chromosome. Construct two
chromosomes identical to the ones you made previously. Each half of the duplicated
chromosome is called a chromatid. Join both red chromatids at the centromere to form a pair
of sister chromatids. Repeat for the yellow chromosome.
4. Place a pair of plastic centrioles, at ninety degree angles, just outside of your nuclear
membrane. The centrioles also replicate during interphase so place another pair next to them
in your cell.
Did you know? B. Prophase
What happens:
Scientist have discovered checkpoint mechanisms that ensure each step in the mitotic process is properly executed before the cell moves onto the next phase. Chromatin condenses within the nucleus and chromosomes become visible. Centrioles
migrate to opposite poles (sides) of the cell and spindle fibers begin to form. As the spindle
fivers appear, the nuclear membrane disappears. The spindle fibers attach to the centromere
region of each chromosome.
To simulate:
1. Move your two pairs of centrioles to opposite poles (sides) of the cell (your desk).
C. Metaphase
What happens:
The chromosomes line up in the middle of the nucleus along the metaphase plate. The
centromeres of each sister chromatid are attached, by spindle fibers, to the centrioles at opposite
poles of the cell.
To simulate:
1. Center your chromosomes along an imaginary metaphase plate with the centrioles still at
opposite poles of the cell.
Adapted from WARDS Mitosis & Meiosis Simulation Laboratory. D. Anaphase
What happens:
Did you know? Many human cancers are likely to stem from defective mitotic checkpoints. The chromatids of each chromosome separate at the centromeres and move to opposite poles of
the cell, forming daughter chromosomes.
To simulate:
1. Separate and move the centromeres of each chromosome toward opposite poles of the cell.
Notice how the arms of each chromosome trail the centromeres to the poles.
E. Telophase and Cytokinesis
What happens:
The spindle apparatus disappears. Nuclear membranes begin to reappear, forming two separate
nuclei; one for each daughter cell. The chromosomes uncoil and become diffuse chromatin.
Cytokinesis begins and separates the cytoplasm into two discrete daughter cells.
To simulate:
1. Move one red strand and one yellow strand to the centrioles it was heading toward during
anaphase. Imagine a cleavage furrow developing between each nuclei and separating the cell
into two daughter cells.
2. Note how each cell now contains one red and one yellow chromosome, as well as one pair of
centrioles, exactly like the cell with which you began.
Activity #2: Meiosis I & II
Use Analysis Sheet #2: Meiosis to diagram each stage of meiosis as you simulate it in this
exercise.
Meiosis I
A. Interphase I
What happens:
Did you know? The segregation of alleles in a diploid organism ensures that offspring receive genes from both parents, increasing the genetic variability of the offspring. DNA replication occurs, resulting in the formation of paired chromatids. Centrioles, and other
cell organelles, replicate as well.
Adapted from WARDS Mitosis & Meiosis Simulation Laboratory. To simulate:
1. Construct two strands of seven red pop beads and attach each strand to a red centromere.
Repeat with two strands of seven yellow pop beads and a yellow centromere.
2. Picture an imaginary boundary in the center of your desk. This boundary will represent the
nuclear membrane. Place the chromosomes in the center of the imaginary nucleus.
3. DNA replication occurs, producing a duplicate of each chromosome. Construct two strands
identical to the ones you made previously. Each half of the duplicated chromosome is called
a chromatid. Join both red chromatids at the centromere to form a pair of sister chromatids.
Repeat for the yellow chromosome.
4. Place a pair of plastic centrioles, at ninety degree angles, just outside of the nuclear
membrane. The centrioles also replicate during interphase so place another pair next to them
in your cell.
Did you know? B. Prophase I
What happens:
Crossing over serves as a mechanism for further genetic variation by re-­‐organizing the chromosomes. New combinations of genes can be created, often affecting the phenotype of the offspring. A process called synapsing occurs in which homologous chromosomes move close together and
pair up along their entire length. A tetrad, consisting of four chromatids is formed. Centrioles
move to opposite poles of the cell and the nuclear membrane begins to break down.
To simulate:
1. Align your homologous chromosomes and entwine them in the center of the nucleus.
2. Move your centrioles to opposite poles of the cell.
3. Snap three beads off of one red chromatid and exchange them with three beads on a yellow
chromatid. This simulates crossing over.
C. Metaphase I
What happens:
Chromosomes disentangle and become aligned in the center of the cell in homologous pairs.
To simulate:
1. Disentangle the entwined homologous chromosomes and place them side-by-side in the
center of the cell.
Adapted from WARDS Mitosis & Meiosis Simulation Laboratory. D. Anaphase I
What happens:
The homologous chromosomes separate and are drawn to opposite sides of the cell by spindle
fibers.
To simulate:
1. Move each homologous pair toward its respective centrioles. Move the chromosome pairs by
the centromere, noting how the chromosome arms trail the centromere as movement occurs.
E. Telophase I
What happens:
During meiosis, cell division occurs and centrioles replicate , resulting in two daughter cells still
containing paired chromatids.
To simulate:
1. Keeping each paired strand near its respective centrioles, create an imaginary line around
each paired strand, representing two new daughter cells. Duplicate the centrioles for both
daughter cells and place them next to the original centrioles.
Meiosis II
F. Interphase II
What happens:
DNA replication DOES NOT occur during the second interphase stage of meiosis.
To simulate:
1. Leave the daughter cells as they were after telophase I.
G. Prophase II
What happens:
The centrioles move to opposite poles of both daughter cells. The chromosomes move toward the
center of the daughter cells.
Adapted from WARDS Mitosis & Meiosis Simulation Laboratory. To Simulate:
1. Move the centrioles to opposite poles of each daughter cell. Place the centromeres of the
paired strands in the center of each daughter cell.
H. Metaphase II
What happens:
All of the chromosomes line up, single file, in the center of the cell.
To simulate:
1. Center the paired strands along an imaginary line across the center of the cell. Line up the
strands so they are centered in each daughter cell.
I. Anaphase II
What happens:
The chromatids of each paired strand separate and are drawn to opposite poles of the cell. Each
chromatid, with a well-defined centromere, is now a chromosome.
To simulate:
1. Separate each paired strand at its centromere. Move each strand toward its respective
centrioles, noting how the chromosome arms trail the centromere as it moves towards each
pole. Repeat this procedure for both daughter cells from meiosis I.
J. Telophase II and Cytokinesis
What happens:
Cell division is completed and four daughter cells are formed. Each contains half of the
chromosome number of the original parent cell. A nuclear membrane forms around each cell’s
chromosomes and the daughter cells from meiosis I finish dividing completely. Centrioles
remain outside the nuclear membrane of each of the four daughter cells.
To simulate:
1. Place each chromosome strand near its respective centrioles. Imagine a nuclear
membrane around each chromosome and a complete division in the daughter cells from
meiosis I, resulting in the four daughter cells.
Adapted from WARDS Mitosis & Meiosis Simulation Laboratory.