Onion root tip mitosis

GCSE: Biology

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8. Remove the slide from the steam bath and
further flatten the cells by applying firm pressure
from above while the slide is being held between
the folds of a mat made from sheets of tissue
paper. This will also expel the excess stain from
under the cover slip, as well as spreading the
chromosome content of dividing cells in an even
layer.
9. This slide may be used for observation for about
30 minutes without sealing. Its usefulness can be
extended to 2-3 days if the slide is sealed off by
nail varnish. The initial stain may intensify upon
storage.
10. When examining the preparation, correct
lighting is important and green light is most
beneficial. Very good squash preparations can be
examined with an oil-immersion lens.
Note
1. The above method does not require a long period
of fixation. Alternatively, the plant material can
be fixed for 24 hours in Carnoy’s fixative. The
fixed material is then stained by warming it in
aceto-lacmoid + HCl stain for five minutes. HCl
is important in aiding the penetration of the stain
by macerating the tissues. Lack of fixation
sometimes results in rather bubbly
chromosomes, which occasionally appear
double. In such case, care is required in
interpreting the preparations.
76.........Practical work
Preparation of Reagent
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