AP Biology
AP Lab Seven: Mitosis and Meiosis
Name_________________________________________
In this lab we will investigate the stages of mitosis and meiosis and explore different properties of cell
reproduction. You will be working with microscopes and a species of fungus called Sordaria fimicola
Procedure
Part 7A: Modeling Mitosis and Meiosis with play-doh.
1. Roll out four long strands of clay (two of one color, two of another) at
least 10 cm long to represent two chromosomes (one from each
parent), each with two chromatids. Roll out four additional short
strands of clay (two of one color, two of another) no more than 5 cm
long to represent two short chromosomes (one from each parent), each
with two chromatids.
2. Mitosis. On a plain white piece of paper, arrange the chromosomes to
show the four stages of mitosis (prophase, metaphase, anaphase,
telophase). Sketch each of these in Table 7.1.
3. Meiosis. Now you will arrange and sketch in Table 7.1 your
chromosomes to show the eight stages of meiosis (prophase I,
metaphase I, anaphase I, telophase I, prophase II, metaphase II, anaphase II, telophase II). Pay
attention to the following special steps.
a. During prophase I, don’t forget to show crossing over. Remove a small, equal section of one
chromatid from each color. Reattach these sections to their opposite, homologous
chromatids (see picture to the right).
b. During metaphase I be sure to line up homologous chromosomes next to each other,
whereas in metaphase II be sure to line up chromosomes single file.
c. During anaphase I be sure to move homologous chromosomes to separate centrioles,
whereas in anaphase II be sure to move chromatids to separate centrioles.
d. During telophase I be sure to end with two cells, whereas in telophase II be sure to end with
four cells.
Part 7B. Time in Cell Reproduction
1. Working with a partner, one person will be observing cells in the microscope while the other is
recording their observations
2. Using an onion root tip cell (l.s. slides are best), orient your slide so that you can see cells in the
full frame of view. You want to be near the tip of the onion root (where more mitosis is
occurring) but have as many cells in the field of view as possible that are distinguishable as
either interphase or mitosis. In other words, you want as few blank cells as possible.
3. Observe every cell in high-power field of view and determine which phase of the cell cycle it is
in. Tell your partner which phase you view so that they may record a tally in Table 7.2.
4. You need to count and record the entire frame of view AND you need to count at least 200 cells.
If either of these has not happened when the entire field has been counted, switch places with
your partner. Find a new frame of view and repeat step 3. You should count and record at least
200 total cells.
a. *Note: Do not stop counting when you reach 200 if there are still more cells in your
frame of view. You should both count all the cells in the frame and make sure your
total number is at least 200.
5. Calculate the percentage of cells in each phase. Record in Table 7.2.
6. It takes on average 24 hours (1,440 minutes) for onion root tip cells to complete the cell cycle.
Calculate the amount of time spent in each phase of the cell cycle from the percentage of cells
in that stage during one life cycle.
7. Draw and label a pie chart of the onion root tip cell cycle using the data from Table 7.2.
Part 7C. Crossing Over During Meiosis in Sordaria.
Sordaria fimicola is a fungus that is a haploid organism for most of its life. It becomes diploid only when
the fusion of the two mycelia (filament-like groups of cells) of two different strains results in the fusion
of the two different types of haploid nuclei to form a diploid nucleus. The diploid nucleus must then
undergo meiosis to resume its haploid state.
Meiosis, followed by one mitotic division in Sordaria results in the formation of eight haploid ascospores
contained within a sac called an ascus. Many asci are contained within a fruiting body called a
perithecium (ascocarp). When ascospores are mature, the ascus ruptures, releasing the ascospores.
Each ascospore can develop into a new haploid fungus. **See Figure 3.1 for an image of the life cycle of
Sordaria.
1. The photographs you will observe show the results of a cross between a wild-type Sordaria
(black) and mutant Sordaria (tan).
a. The included images show the process of how meiosis and mitosis result in the series of
ascospores you will view in the pictures.
2. Look through the cards and find 50 hybrid asci (asci that show cells with both black and tan
ascospores). Some of these hybrids underwent crossing over; some did not.
3. Record each hybrid asci you find in Table 7.3. Be sure to record whether the asci has undergone
crossing over or not.
4. A map unit is an arbitrary unit of measure used to describe relative distances between linked
genes. One map unit = 1% of the distance from the centromere to the tip of the chromosome.
Logically, the further away a gene is from the centromere, the more likely the gene is to cross
over. You will use the % of asci showing crossing over to find the relative distance between the
gene for spore coat color and the centromere.
a. If a specific gene undergoes crossing over in 50% of the offspring, its logically 50% of the
distance between the centromere and the end of the chromatid.
5. To calculate the map distance, divide the % of crossover asci by 2. You divide by two because
only half of the spores in each ascus are the result of a crossover event.
Part 7D: Karyotyping
1. A karyotype is a photograph of chromosomes taken from a cell undergoing mitosis. Karyotypes
are often used to quickly ascertain genetic traits (genders, any possible mutations, etc).
2. Obtain two karyotypes from Mr. Marshall (one is a normal karyotype, one has a defect of some
sort. Be sure to record the labels of your karyotypes for identification later.
3. Cut out each of the individual chromosomes in the karyotype and arrange according to relative
length.
4. Attempt to find homologous chromosomes based on the banding patterns of chromosomes.
Organize these together.
5. Attempt to order and label the chromosomes. Tape your chromosomes to the page included
when you received your lab.
a. If your karyotype came from a male, remember they will have one X and one Y
chromosome. If your karyotype came from a female, remember they will have two X
chromosomes.
b. The X chromosome length is between chromosome # 7 and #8.
c. The Y chromosome is the shortest chromosome.
6. Once your karyotypes are organized, try to identify the gender and the relative health of the
cell. One karyotype is normal, the other karyotype displays a disorder of some sort.
Post-Lab Questions
1. What are three similarities between mitosis and meiosis? What are three differences? Be
specific!
2. How would your results of the time in reproduction differ if you left the area of the root tip and
instead studied, for example, the cells in the onion leaf?
3. Which stage of cell division do onions spend the most time in? The least? How do you know?
4. Identify the gender and condition of each of your karyotypes. Be sure to include the labels on
the original paper.
Lab Book Requirements
1. Date of lab
2. Title of lab
3. Objective of this lab
4. Manipulated and responding variables for part 7B only
5. At least three controls for part 7B only
6. Hypothesis for part 7B only
7. Table 7.1
8. Table 7.2
9. Table 7.3
10. Pie graph from 7.2
11. Two karyotype charts (Don’t attach them to the lab book, they’re too huge.)
12. Conclusion
13. What is the next experiment you could perform?
14. Answers to post-lab questions
Table 7.1 Stages of Mitosis/Meiosis
Prophase
Prophase I
Prophase II
Metaphase
Metaphase I
Metaphase II
Anaphase
Anaphase I
Anaphase II
Telophase
Telophase I
Telophase II
Table 7.2 Time in Cell Division
Number of Cells
Field 1
Field 2
Field 3
(if necessary)
(if necessary)
Total
% of Total
Cells
Counted
Time in Each
Stage
Interphase
Prophase
Metaphase
Anaphase
Telophase
Total Cells Counted
Table 7.3 Sordaria Crossing Over
Number of 4:4
Asci
Number of Asci
Showing Crossover
Total Asci
% Asci Showing
Crossover
Gene/Centromere
Map Distance