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Mitosis in Onion root tip
Cell is the structural and functional unit of life. The word cell was coined by Robert
Hooke. Cells are categorised as: simple non- nucleated prokaryotic cells and complex nucleated
eukaryotic cells. Cell division is a process by which a parent cell divides into two or
more daughter cells. The type of cell division that usually occurs in eukaryotic somatic
cells is called Mitosis. This is a small part of a large complex cell division.
Mitosis is a process in which a eukaryotic cell separates its replicated chromosomes
in the cell nucleus into two identical sets as two nuclei, which is immediately followed
by cytokinesis. This helps the cells to share the chromosomes equally into two. The separation
of nucleus (Karyokinesis) and separation of cytoplasm and other cell organelles (cytokinesis)
together forms the Mitotic phase of the cell division.
The process of mitosis comprises of different stages: Prophase, Metaphase, Anaphase and
Telophase.
Onion roots are commonly used for viewing mitosis in labs. Onion roots are very easy
to grow in large numbers. The cells at the tip of the root actively divide and thus there
will be many cells in mitotic phase. Therefore onion root tips are excellent source for viewing
mitosis. Chromosomes are generally not visible, for that we have to use DNA specific stains
like Feulgen stain and Acetocarmine.
Materials required
Onion plant with root Scissors, forceps & razor blade
Eppendorf tube 1 N HCl
Pasture’s pipette Feulgen stain/Acetocramine
Dissection probe with wooden back Water bath
Distilled water Microscope
Microscopic slides and cover slips
Procedure
Ensure all materials mentioned are on hand. Using the scissors cut about 1 cm of two newly
sprouted roots tips, and transfer them into the eppendorf tube using the forceps.
Clean the root tips using distilled water. Add 1N HCl into the eppendorf tube using the
dropper. Close the tube and place it in a floater and
keep this incubated in a 60 0C water bath for 12 minutes.
After incubation remove the tube from the water bath.
Using the Pasture’s pipette draw out the HCl from the eppendorf tube and discard it
under running tap water. Pour a few drops of water over the root tips
in the eppendorf tube. Close the tube and shake it slightly. Then draw out the water
using the Pasture’s pipette. Repeat this process three times.
Now pour 2-3 drops of Feulgen stain or Acetocarmine stain into the tube and keep it incubated
for 12 minutes. Draw out the Feulgen stain using a pasture’s
pipette and pour a few drops of water. Close the tube and shake it slightly. Then draw
out the water using the Pasture’s pipette. Repeat this process three times.
You will notice that the root tips have turned red.
Using the forceps carefully transfer a root to the microscopic slide. Then cut the unstained
part of the root using a razor blade and discard it.
Place the cover slip over it. Using the wooden part of dissection probe
push down on the cover slip. The root tip is squashed and spreads out to a diameter
of 0.5cm to 1cm. Place the slide over the slide holder of the
microscope. Adjust the microscopic lens to 10X and notice
the result. To get a clearer view zoom the microscopic
lens to 40x. You can identify all stages of mitosis through
this view.