Biology Grades 9-12
5. The genetic composition of cells can be altered by
incorporation of exogenous DNA into the cells. As a basis for understanding
a. Students know the general structures and functions of DNA, RNA, and protein.
d.* Students know how basic DNA technology
(restriction digestion by endonu cleases, gel electrophoresis, ligation, and
transformation) is used to construct recombinant DNA molecules.
Investigation and Experimentation Standards:
1. Scientific progress is
made by asking meaningful questions and conducting careful investigations. As a
basis for understanding this concept and addressing the content in the other
four strands, students should develop their own questions and perform
investigations. Students will:
a. Select and use appropriate tools and technology (such
as computer-linked probes, spreadsheets, and graphing calculators) to perform
tests, collect data, analyze relationships, and display data.
l. Analyze situations and solve problems that require
combining and applying concepts from more than one area of science.
Preparing the agarose gel
• Measure 1.25 g Agarose powder and add it to a 500 ml flask
• Add 125 ml TAE Buffer to the flask. (the total gel volume well vary
depending on the size of the casting tray)
• Melt the agarose in a microwave or hot water bath until the
solution becomes clear. (if using
a microwave, heat the solution for several short intervals - do not let the
solution boil for long periods as it may boil out of the flask).
• Let the solution cool to about 50-55°C, swirling the flask
occasionally to cool evenly.
• Seal the ends of the casting tray with two layers of tape.
• Place the combs in the gel casting tray.
• Pour the melted agarose solution into the casting tray and
let cool until it is solid (it should appear milky white).
• Carefully pull out the combs and remove the tape.
• Place the gel in the electrophoresis chamber.
• Add enough TAE Buffer so that there is about 2-3 mm of buffer over the gel.
Loading the gel
• Add 6 ml of 6X Sample Loading Buffer to each 25 ml PCR reaction
• Record the order each sample will be loaded on the gel,
including who prepared the sample, the DNA template - what organism the DNA
came from, controls and ladder.
• Carefully pipette 20 ml of each sample/Sample
Loading Buffer mixture into separate wells in the gel.
• Pipette 10 ml of the DNA ladder
standard into at least one well of each row on the gel.
Running the gel
• Place the lid on the gel box, connecting the
• Connect the electrode wires to the power supply, making sure
the positive (red) and negative (black) are correctly connected. (Remember – “Run to Red”)
• Turn on the power supply to about 100 volts. Maximum allowed voltage will vary
depending on the size of the electrophoresis chamber – it should not exceed 5 volts/ cm between electrodes!
• Let the power run until the blue dye approaches the end of
• Turn off the power.
• Disconnect the wires from the power supply.
• Remove the lid of the electrophoresis chamber.
• Using gloves, carefully remove the tray and gel.
• Using gloves, remove the gel from the casting tray and place
into the staining dish.
• Add warmed (50-55°) staining mix.
• Allow gel to stain for at least 25-30 minutes (the entire
gel will become dark blue).
• Pour off the stain (the stain can be saved for future use).
• Rinse the gel and staining tray with water to remove
• Fill the tray with warm tap water (50-55°). Change the water several times as it
turns blue. Gradually the gel will
become lighter, leaving only dark blue DNA bands. Destain completely overnight for best results.
• View the gel against a white light box or bright surface.
• Record the data while the gel is fresh, very light bands may
be difficult to see with time.
1. How would it affect the spread of the bands to use a gel of increased concentration?
The tighter gel matrix reduces effective separation of larger fragments but more effectively will separate the smaller DNA fragments.
2. If the two suspects had been identical twins, how would it have influenced the results?
The two suspects would be so alike that it might not be possible to determine which one committed the crime.
3. If more than two rows of bands look alike, what could have happened during the gel-loading?
Someone may have forgotten to change tips/ pipets between samples which will mix the DNA in one well.
4. Why do some DNA fragments move farther than others?
The shorter fragments will move farther.
5. Why do people have differences in their band pattern?
This is due to junk DNA and having differences at where the restriction sites are cut.