Modeling Meiosis
Essential Question:
How do our cells determine who we are?
Today: Modeling Meiosis
Learning target: Describe 3 key differences
between mitosis and meiosis.
Background Information:
Today we are going to do a step by step simulation of
meiosis. We will be working with the chromosomes
of a Puffle, an imaginary organism…...
1. If the Puffle has a diploid chromosome number of four, what will the haploid
2
chromosome number be? __________________
2. Place a large paper plate in the center of your work space. Imagine that this is one sex cell
in a Puffle. The boundary of the plate is the cell membrane.
3. You are going to create a diploid nucleus containing two pairs of chromosomes. First,
divide each of your four balls of colored clay in half.
4. Take one-half of each ball and roll it between your hands to form four elongated, snakelike
chromosomes. Make the red and blue chromosomes as long as your index finger. Make the
green and yellow ones half that length. Do the same thing with the other half of your clay.
Large paper plate
5. Remember that a chromosome is made of tightly coiled strands of DNA. Within each
chromosome there are many, many genes. The chromosomes within each pair are said to be
homologous, meaning similar but not necessarily the same. Homologous chromosomes contain
the same genes but not necessarily the same alleles. For instance, two homologous
chromosomes might contain the gene which codes for eye color, but the alleles might be
different--like blue eye allele on one chromosome and brown eye allele on the other.
Blue
eye
allele
Brown
eye allele
Homologous
Chromosomes
(1 from mom, other from dad)
6. We are going to examine four traits in the Puffle, specified by four genes. Remember that
genes are segments of chromosomes which code for proteins that cause observable traits
(phenotypes). Table II describes some traits of our imaginary creature and their locations on
each chromosome.
Table II -- Imaginary Traits of the Puffle
Genes on PAIR 1
Fur Color
Fur Type
Green Chromosome G (green fur)
c (straight fur)
Yellow Chromosome g (yellow fur)
C (curly fur)
Genes on PAIR 2
Eye Color
Eyelash length
Blue Chromosome
B (blue eyes)
L (long eyelashes)
Red Chromosome
b (red eyes)
l (short eyelashes)
Table II -- Imaginary Traits of the Puffle
Genes on PAIR 1
Fur Color
Fur Type
Green Chromosome
G (green fur) c (straight fur)
g (yellow fur) C (curly fur)
Yellow Chromosome
Genes on PAIR 2
Eye Color
Eyelash length
B (blue eyes) L (long eyelashes)
b (red eyes) l (short eyelashes)
Blue Chromosome
Red Chromosome
g
G
C
c
B
L
b
l
g
G
C
c
B
b
L
l
7. Label the location of each gene by cutting out the paper labels provided and sticking them on
to the clay as shown above. Cut the paper as close to the letters as you can.
INTERPHASE
8. During interphase, each chromosome is replicated by making another complete set of DNA.
Simulate this replication by creating a matching chromosome (same shape and color) using the other
half of your clay. Label each chromatid with genes so they are exact copies.
9. Connect sister chromatids together at the centromere (center point) by pinching them together as
shown below:
chromatid
g
g
G
G
C
C
c
c
B
B
b
b
L
L
l
l
centromere
chromatid
8
10. How many chromatids are present at this stage?_________
How many
4
2 chromatids.
chromosomes? ____________.
Each chromosome is made of _______
PROPHASE I
11. Pair up each newly replicated chromosome with its homologous partner, forming two tetrads (2
pairs of chromosomes, total of 4 chromatids).
12. Now that homologous chromosomes are near each other, crossing-over can occur. In each
tetrad, place one chromatid over another. Then trade alleles so the colors are mixed.
B B
L
b b
l
L
B B
b b
L l
L l
l
g g
GG
g g
GG
C C
c c
C c
C c
METAPHASE I
13. Imagine that the nuclear membrane has now broken down in your imaginary Puffle cell.
Line the two tetrads (pairs of chromosomes) end to end across the center of the cell. Attach a
piece of yarn stretching from the centromere (center point) of each chromosome to the end of
spindle fibers
the cell nearest to it. What do the pieces of yarn represent? ____________________
centromere
Large paper plate
yarn
14. In a real cell, would the red chromosome always line up on the same side as the green
No. Chromosomes line up in random order,
chromosome? Why or why not? _______________________________________________
like shuffling cards.
__________________________________________________________________________
ANAPHASE I
15. Separate each tetrad and use the spindle fibers to move the homologous chromosomes to
opposite poles of the cell as shown below:
TELOPHASE I
16. Cytokinesis (cell division) occurs to form two daughter cells. These daughter cells are
not haploid or diploid, but some kind of intermediate stage. Arrange your clay
chromosome models on two large paper plates as shown below:
GG
g g
BB
Cc
Ll
bb
Cc
Ll
17. Are the two daughter cells genetically the same or different? Explain.
Different. Chromosomes got mixed up and separated.
________________________________________________________________________
_________________________________________________________________________
MEIOSIS II
PROPHASE II & METAPHASE II
18. Line up the chromosomes in each cell end to end along the center line. Attach spindle
fibers (yarn) to the centromeres (center points) as shown below:
centromere
yarn
ANAPHASE II
19. Separate the two sister chromatids and move them to opposite poles as shown below:
20. What does the yarn represent? What’s its function in real cells?
_______________________________________________________________________
Spindle fibers. Pulls chromatids apart.
_______________________________________________________________________
TELOPHASE II
21. Cytokinesis occurs again, producing a total of four daughter cells. You can show this by
separating the 8 sets of chromosomes on to 4 small paper plates as shown below:
gCBL
Yellow, curly fur
blue eyes
long lashes
gcBl
Yellow, straight fur
blue eyes
short lashes
GCbL
Green, curly fur
red eyes
long lashes
Gcbl
Green, straight fur
red eyes
short lashes
haploid
22. Are these cells diploid or haploid? How do you know ? _____________________
Each have half as many chromosomes as parent cell
_______________________________________________________________________
different
23. Are the four daughter cells genetically the same as each other or different?_________
different
Are they genetically the same as the parent cells or different? ___________________
Are these body cells or gametes (reproductive cells)?___________________________
Gametes (reproductive cells)_
24. Write the genotype and phenotype beneath each of the daughter cells shown in #21.
Cleaning up: Please remove the letter labels from the clay and separate the clay back into four
different color balls so that the next class can use them. Thank you! 
6. We are going to examine four traits in the Puffle, specified by four genes. Remember that
genes are segments of chromosomes which code for proteins that cause observable traits
(phenotypes). Table II describes some traits of our imaginary creature and their locations on
each chromosome.
Table II -- Imaginary Traits of the Puffle
Genes on PAIR 1
Fur Color
Fur Type
Green Chromosome G (green fur)
c (straight fur)
Yellow Chromosome g (yellow fur)
C (curly fur)
Genes on PAIR 2
Eye Color
Eyelash length
Blue Chromosome
B (blue eyes)
L (long eyelashes)
Red Chromosome
b (red eyes)
l (short eyelashes)