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Isolation of Plant Genomic DNA Cheat Sheet by

Isolation of plant (Onion) genomic DNA by a crude method


Isolation of plant (Onion) genomic DNA by a crude method.


A general difficulty in isolating DNA from plant cells is the presence of a cell wall, which requires degrad­ation either physically or enzyma­tic­ally. Specific plant species and tissues may have additional challenges due to starches or phenolic compounds.


Extract genomic DNA from onion.


All DNA isolation methods consist of three steps:
Lysis of cells.
Denatu­ration of histones associated with DNA.
Precip­itation of DNA using an organic solvent like ethanol.

In the described method:
1. A kitchen blender (mixer Grinder) breaks open the cell walls.
2. Detergent degrades the phosph­olipid membranes around the nuclei, releasing the DNA.
3. Detergent, combined with heating, denatures the histones associated with the DNA.
4. Protease hydrolyses the denatured histones into peptides and amino acids.
5. DNA is then precip­itated in ice-cold ethanol, which disrupts DNA-water intera­ctions, causing DNA to precip­itate out of solution.


Washing-up liquid (Deter­gent)
Table salt (3 g)
Water (tap water is suitable)
Very cold ethanol or Isopro­panol (10 ml) (keep in the freezer)
a protease enzyme, (2–3 drops) (Optional)
Plastic funnel
Beakers, 2 (250 ml)
Test tubes, 2
Plastic spoon for stirring the mixture
Chopping board
Knife for chopping onion
Water bath, maintained at 60°C
Mixer Grinder or liquidiser


Dissolve 3g salt in 90ml (about 3.04 oz) water with washing-up liquid.
Add chopped onion (5mm (about 0.2 in) x 5mm) to the solution in a beaker.
Place the beaker in a 60°C water bath for 15 minutes.
Cool the mixture in an ice water bath for 5 minutes, stirring freque­ntly.
Blend the mixture for 5 seconds on high speed in a mixer grinder.
Filter the mixture into another beaker to obtain the DNA-co­nta­ining filtrate.
Option­ally, add 2–3 drops of protease to 10ml (about 0.34 oz) of onion extract in a boiling tube and mix well.
Carefully pour ice-cold ethanol down the side of the boiling tube.
Let the tube sit undist­urbed for a few minutes.
DNA will precip­itate into the upper ethanol layer, appearing as white material.



The photo shows the result of mixing a part of an onion with detergent and salt, and then layering ice-cold ethanol on top of the mixture. DNA appears as the white precip­itate in the alcohol layer.


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