Mitosis and core practical (SNAB)

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  • Created on: 18-03-13 21:00
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By the end of interphase, the cell contains enough cytoplasm, organelles and DNA
to form two new cells.
Nuclear division (Mitosis)
The chromosomes condense, with each chromosome visible as two strands
(chromatids) joined by the centromere.
Microtubules from the cytoplasm form a 3d structure called the spindle.
The centrioles move around the nuclear envelope and position themselves at
opposite sides of the cell; these form the two poles of the spindle, and are involved
in the organisation of the spindle fibres
Signalled by the breakdown of the nuclear envelope.
The chromosomes centromeres attach to spindle fibres at the equator.
The centromeres split, the spindle fibres shorten, pulling the two halves of each
centromere in opposite directions.
One chromatid of each chromosome is pulled to each of the poles.
The chromosomes unravel and the nuclear envelope reforms, so that the two sets
of genetic information become enclosed in separate nuclei.
Cytoplasmic division (Cytokinesis)
As the membrane continues to constrict, the cytoplasm divides forming two
genetically identical daughter cells.
Each cell now possesses an exact copy of each chromosome that was present in
the nucleus of the original cell.
How to prepare and stain a root tip squash in order to observe the stages of
1. Cut a 5mm tip from a growing root (e.g. of a broad bean)
2. Place the tip into a watch glass and add a few drops of hydrochloric acid.
3. Add drops of stain so the chromosomes become darker and easier to see under a
microscope. E.g. Toluidine blue.
4. Place the root tip onto a microscope slide and use a mounted needle to break it
open and spread the cells out thinly.
5. Place a cover slip over it, squash it down gently and then look at the stages of
mitosis under a light microscope.


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