Gr 12 Practical: Extracting DNA from wheat germ.
Name:________________________________
Partner’s Name:________________________
Mark: Group mark
/ 10
The experiment will be conducted in pairs. Each member of the pair must have a completed copy of this
sheet.
DNA EXTRACTION INSTRUCTIONS
You can make a crude extract of DNA from ground wheat, using household products.
STEP 1:
Place 5ml (1 teaspoon) of wheat germ in a 250ml beaker (cup or spice bottle).
Add 25ml (5 teaspoons) of warm (40 - 50 oC) water to the wheat germ and mix non-stop with a wooden
stick (or spoon) for 3 minutes. This allows the cells to be suspended and also allows them to be exposed to
the other reagents/ substances that will be added later.
STEP 2:
Add 1.25 ml (¼ teaspoon) of dishwashing liquid to the cells that have been suspended in water in step 1.
Mix gently with a wooden stick (or spoon) every ½ minute for 5 minutes. The dishwashing liquid breaks
down the cell membranes. Do not let the dishwashing liquid froth and foam in the beaker or cup, as this
may prevent effective extraction of the DNA!
STEP 3:
Remove any foam that may have formed on top of the mixture using a paper towel or spoon.
This is important, as foam on top of the mixture may prevent the ethanol (or methylated spirits) added in
step 4 from mixing effectively.
STEP 4:
Remove the wooden stick (or spoon) from the beaker before adding the ethanol (or methylated spirits).
Tilt the beaker and slowly add an estimated equal volume of ice cold or ethanol (or methylated spirits) to
the mixture by carefully pouring it down the side of the beaker.
Do NOT mix the two layers together. DNA separates (precipitates) at the water-alcohol interface (the
boundary between the water and the alcohol). Therefore, it is crucial to pour the alcohol very slowly so
that it forms a layer on top of the water solution. If the alcohol mixes with the water, it will become too
dilute and the DNA will not precipitate (separate out). After adding the ethanol ( or methylated spirits) to
the mixture, DNA rises to the surface. This may take a few minutes
STEP 5:
Use the wooden stick (or spoon) to fish the DNA out of the beaker and transfer it to a petrie dish (or small
pill bottle or saucer) and view under a dissecting microscope.
If you want to keep the DNA, store it in methylated spirits (alcohol) in a sealed tube or air dry it on paper
towels or filter paper.
Observe and analyse the threads of DNA and answer questions below.
Have the rubric below marked by your teacher.
STEP 6:
The second part of this practical will be for you to design your own experiment following this procedure.
OBSERVATIONS
1
Use between 3 and 5 words to describe what the wheat germ DNA that you pulled out of the
beaker looks like.
______________________________________________________________
2
Mention TWO precautions you would need to take in step 4.
______________________________________________________________
______________________________________________________________
ASSESSMENT
CRITERIA
Organisation - work
through procedure in
orderly manner
Ability to use
apparatus or
equipment
Results / Final
product
Workstation
Responses to
questions based on
experimental work
TOTAL
0
Procedure
disorganised
1
Procedure
partially
organised
Apparatus
Apparatus
always used
sometimes used
incorrectly
correctly
No results
Partially correct
results
Workstation is Work station is
not cleaned up partly clean and
tidy
No answers
Answers filled in
provided to
but incomplete
questions
or partly
inaccurate
2
Procedure organised
efficiently
Apparatus always
used correctly
All results correct
Workstation is left
clean and tidy
Answers accurate and
complete
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