Name
Date
Teacher
Assessment type: Investigation
Task: The significance of meiosis
An important feature of meiosis is the variation that is introduced as homologous
chromosomes pair up along the equator before the first division of the cytoplasm.
In this investigation you will work through the stages of meiosis by modelling the
chromosome sets. This will familiarise you with some of the details of meiosis and its
significance in variation.
What to do
To complete this task you will need to use poppit beads or something to represent light
and dark beads to make three pairs of chromosomes. Carefully follow the procedure below
and then answer the questions.
Materials

poppit beads or something to represent light and dark beads

pipe cleaners

coin, paper, scissors

thin texta or felt-tip pen.
Procedure
Step 1
Use the poppit beads or a substitute to make three pairs of chromosomes.
The three chromosome pairs need to be of different lengths and colour-coded.
For example, you could use four bead strands, six bead strands and eight bead
strands as shown below. In this example the darker bead strands represent
paternal chromosomes and the lighter bead strands represent maternal
chromosomes.
Beads modelling chromosomes
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Step 2
To represent the chromosomes duplicating themselves, make a second set of
matching beads and join them together using a pipe cleaner as shown below.
This will represent a pair of chromatids joined at the centromere during
metaphase I.
Beads modelling chromosomes joined at the centromere
Step 3
Assume each bead represents a gene.
Use a texta to mark the position of a gene in each chromosome as shown
below.
Maternal and paternal chromosomes showing position of a gene
You can now mark the position of a gene in each chromosome using your texta or felt-tip
pen as shown in the table below.
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Bead strand
maternal
paternal
10
AA
aa
8
BB
bb
5
CC
cc
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Step 4
Assume your organism is beginning to produce gametes by meiosis. The
following will then occur:

members of each pair come together and lie alongside one another in
homologous pairs

a spindle develops across the cell from pole to pole and an imaginary
equator is formed

the chromosomes (still in homologous pairs) line up across the equator with
one chromosome of each pair on one side of the equator, and one on the
other.
The arrangement of the chromosomes at the equator will determine which one
of each pair moves to each daughter cell.

Use your marked chromosomes to simulate meiosis in the following steps.

Use a sheet of blank paper to represent the cell (assume the nuclear
membrane has broken down).

Draw a line across the middle of the paper to represent the cell equator.

Arrange your chromosomes in homologous pairs either side of the cell
equator as shown below.
Maternal and paternal chromosomes arranged either side of the cell equator
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The first division of meiosis
Work through the sections and answer the questions.
How do the maternal and paternal chromosomes separate from one another during
meiosis?
There are two alternative hypotheses which can be proposed to answer this question.
Hypothesis 1: After pairing of the homologous chromosomes, all the maternal
chromosomes go to one daughter cell and all the paternal chromosomes go to the other
daughter cell.
Hypothesis 2: After pairing of the homologous chromosomes, the maternal chromosomes
and the paternal chromosomes separate more or less at random. Some maternal and
some paternal chromosomes go into one daughter cell and the remainder into the other.
Move the chromosome according to the first hypothesis. All the maternal chromosomes
should be on one side (left or right) of the equator and all the paternal chromosomes on
the other.
1.
How many different combinations of maternal and paternal chromosomes will there
be in the gametes if all the maternal chromosomes were to move to one end of the
spindle and all the paternal chromosomes to the other? Explain.
You will now arrange the chromosomes according to the second hypothesis.
Separate the maternal and paternal chromosomes at random, with some maternal and
some paternal chromosomes going into one cell and the remainder into the other.
To do this:

choose a pair of chromosomes and toss a coin

if ‘heads’, move the maternal chromosome to the far right of the equator and the
paternal chromosome to the far left of the equator

if ‘tails’, move the maternal chromosome to the far left and the paternal chromosome
to the far right

repeat the toss for the next pair of chromosomes until all three have been separated

draw a diagram to show the random separation of maternal and paternal
chromosomes.
Leave the chromosomes (consisting of two chromatids) joined at the centromere in this
arrangement to continue ‘meiosis’ after answering the following questions.
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2.
Would it be possible to get all the maternal chromosomes to one side of the equator
and all the paternal chromosomes to the other by chance?
3.
If so, how often would you expect this to happen (in terms of probability)?
Separation of the chromosome pairs

At this point in meiosis the paired chromosomes move apart towards opposite poles of
the spindle.

Cut the paper into two equal parts to represent the daughter cells.

Each daughter cell will contain three pairs of chromatids still attached at the
centromere.
This completes the first division of meiosis.
The second division: Separation of the chromatids
The second division of meiosis involves the separation of the chromatids.
To do this:

arrange the pairs of chromatids along each equator as shown below

divide each chromatid at the centromere by undoing the pipe cleaners

move the chromatids apart by placing one each side of the equator

cut the two paper daughter cells.
The second division is now complete and four haploid gametes are produced.
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4.
How many chromosomes did the original cell contain?
How many chromosomes did each of the gametes contain?
How many gametes result from the meiotic division of the original cell?
Are gametes haploid or diploid?
5.
Write down the combinations of the characteristics (ABC, AbC etc) which occurred in
the gametes produced in this activity.
6.
Could repeating meiosis give any different combinations of characteristics?
If so, what are they?
You may choose to work this out mathematically or you may wish to repeat the
procedure until you have recorded all the possible combinations.
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Studying the data
Now consider what happens as a result of random separation of maternal and paternal
chromosomes.
7.
How many different kinds of gametes (with respect to the combinations of
characteristics they carry) were produced in your own trial?
8.
How many possible kinds of gametes could one get from a parent with two
alternative forms for each of the three characteristics on the chromatids (parent
AaBbCc)?
9.
In practice, matings of the kind you have just modelled almost always produce
offspring with different combinations of the three pairs of characteristics involved.
Which is more likely to be taking place: separation of maternal and paternal sets or
random separation of the chromosome pairs? Explain.
10. In this task you worked through the stages of meiosis and its significance in variation
by modelling the chromosome sets. Briefly comment on the limitations of
experimental design when using models to represent real-life events.
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11. The members of a litter of puppies or a litter of kittens produced by mating usually
produce several different coat colours as shown below.
Use your knowledge of meiosis and random fusion of gametes to explain the presence of
several different coat colours amongst each of these litters?
12. Use an example of an Australian organism to demonstrate the significance of
variation in the gene pool of a population in a changing environment.
List the sources of variation in the gene pool.
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