Name__________________
Biology 211 Intro Molecular and Cell Biology
Mitosis Laboratory
Purpose: To prepare slides of onion root tips demonstrating the stages of
mitosis (somatic cell division) and observe various cell types undergoing mitosis.
Reading: Campbell et al., Chap. 12
Background:
Mitosis is the process of cell division that occurs in somatic (body) cells.
In mitosis, a cell divides to give two daughter cells, essentially identical to the
parent cell. Mitosis results in an equal distribution of hereditary material and
usually an equal distribution of the cell contents. All of us began life as single
cells. These cells divided by mitosis to become 2, then 4, then 8, then 16 cells
and so on. At some point some of these cells started to differentiate into other
cell types to form our various tissues.
In cancer, the process of cell division has gone awry. To begin to
understand the kinds of changes that occur that allow cells to grow and divide
past their normal "checkpoints", it is crucial to understand the process of division
in normal cells.
Materials:
onion root tips
watch glasses
acetocarmine stain (1% in 45% acetic acid, boiled 5 min. and filtered)
1 M HCl
razor blades
forceps
slide warmer
slides, coverslips
compound microscopes, lens paper
mitosis slides: Allium (onion) root tip, whitefish blastula
Procedure: Source: Mertens and Hammersmith (2001) Genetics Laboratory
Investigations, twelfth edition. Prentice Hall.
1. Prepare slides of onion root tip.
a. Clip the terminal 1 cm of the root tip from a growing onion bulb.
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b. Place several drops of 1 M HCl in a watch glass.
c. Place the terminal 3 mm of the onion root in the HCl solution.
d. Incubate at room T for 3-5 min.
e. Using a forceps, transfer the root tip to a drop of acetocarmine stain on a
clean slide.
f. Using a razor blade or sharp scalpel, cut off and retain the tip-most 1 mm of
the root. Chop the root tip into many pieces with the razor blade.
g. Apply a clean cover glass to the slide and heat it gently for 5 min. on a slide
warmer.
h. Cover the slide with a paper towel and push downward firmly with your thumb
over the cover glass.
i. Examine with the light microscope at low power and high power. Look for cells
where the nuclei have stained red-purple.
Interphase cell
Label: Nucleus, nuclear envelope, cell membrane
Mitotic cell: For extra credit identify and draw an onion root cell from your slide
in a stage of mitosis
See instructor or lab assistant for help locating mitotic cells.
2. Review the process of mitosis using the mitosis poster or laminated diagrams.
3. Observe mitosis on prepared slides of onion root tip and whitefish. Identify
cells in the stages of interphase, prophase, metaphase, anaphase, and
telophase.
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
Interphase: Chromatin appears dispersed, DNA replication occurs.

Prophase: Chromatin condenses, chromosomes become visible, nuclear
membrane breaks down, spindle starts to form.

Metaphase: Chromosomes line up on the spindle in the center of the cell
(on metaphase plate).

Anaphase: Chromosomes are separated at their centromeres, spindle
pulls them toward opposite poles.

Telophase: Chromosomes recondense, new cell wall forms between
daughter cells (plant cells) or cell membrane pinches off (animal cells).
Organism ____________. Draw cells in each stage for either onion or whitefish.
Interphase
Label: Nucleus, chromatin, nuclear envelope, cytoplasm
Prophase
Label: Chromosomes, spindle
Metaphase
Label: Chromosomes, spindle, metaphase plate
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Anaphase
Label: Chromosomes, microtubules
Telophase
Label: Nuclear membrane, cell membrane, chromosomes
4. Ask yourself the following questions as you study the slides:
a. Chromosome division: When do the following changes take place?
DNA replication occurs
Chromosomes condense
Chromosomes disperse
Sister chromatids are attached at the
centromere
Centromere divides and sister
chromosomes separate
b. Changes in cell structure: When do the following events take place?
Breakdown of nuclear envelope
Spindle forms
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Nuclear membrane reforms
Cell membrane reforms
Cell wall is formed
c. What are some of the differences between the process of mitosis as it
occurs in plants (onion) and animals (whitefish)?
Assignment: (20 points). Complete the drawings and tables above.
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