Download DNA Fingerprinting Lab

One test used in forensic labs is DNA fingerprint. It is also
called a DNA profile. Analysts use the DNA profile from
potential suspects and compare it against DNA found at a
crime scene. There’s DNA profiling for paternity tests.
These days you can send a sample of DNA and find out your
ancestry to learn more about your origins. This is a very
conclusive test because DNA is specific to each individual
(unless you are an identical twin).
HOW ARE DNA FINGERPRINTS MADE???
✓ The process begins with a sample of DNA
✓ Isolate & replicate the DNA
http://learn.genetics.utah.edu/content/labs/pcr/
✓Cut the DNA with restriction enzymes (each enzyme
looks for a specific pattern)
✓Place fragmented DNA in the wells of a polyacrylamide
gel and electrophoresis is performed (negative charge on
top by wells and positive charge on bottom)
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HOW DOES IT WORK???
•DNA has a negative charge,
so the fragments of DNA are
attracted toward the positive
charge (bottom of gel).
•The smaller fragments of
DNA will be able to move
quicker toward the bottom
than the larger pieces.
•Thus DNA is separated by
size (smaller pieces toward
the bottom and the larger
pieces toward the top).
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http://www.dnalc.org/resources/animations/gelelectrophoresis.html
http://www.pbs.org/wgbh/nova/sheppard/cleared.html
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ON PAPER WHAT WOULD IT
LOOK LIKE?
✓You would be given a sequence of DNA and told of a restriction
enzyme that cuts at a particular sequence of base pairs.
✓You would then make a cut in the DNA (draw a line) to make
the DNA fragments (you will be the restriction enzyme).
✓Remember: Restriction enzymes only cut 5’ to 3’
EXAMPLE: Restriction enzyme BAM H1: AATT
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GAATTCGGAATTCCATTGGTAAGAATTCGGTA
CTTAAGCCTTAAGGTAACCATTCTTAAGCCAT
✓Now count the number of DNA bases between each of the cut
sites using the top DNA sequence only.
There are 7 bp between the 1st two cuts & then there
are 15 bp between between the 2nd and 3rd cuts!!!!
✓Based on the counted number of base pairs in the DNA fragment,
make a band at the appropriate spot in the gel using the ladder.
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DNA Fingerprints of a family (D=daughter, S=son)
What can you say about this family
looking at their DNA fingerprints??
D1 & S1 are the biological offspring of both parents
D2 is the biological child of mom but not dad
S2 is not the biological son of either of the parents tested
There’s been
a murder!!!
It’s time for some Annotating 
• In the lab packet you need to do the
following:
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Circle chemicals needed
Underline the equipment needed
Highlight the purpose of this lab
Next to each step, write why you are doing this.
Procedures for Casting Gels
Seal the ends of the gel tray securely with strips of standard masking tape. Press the
tape firmly to the edges of the gel tray to form a fluid-tight seal.
Place the gel tray flat on the lab table (Make it as level as possible).
Place the plastic comb into the appropriate slot of the gel tray. Gel combs should be
placed within ½ inch of the end of the gel casting tray. The combs will form the
wells into which the samples of DNA will be loaded.
Pour enough agarose to cover the gel comb teeth or to a depth of 0.5-0.75 cm. Do
not move or handle the gel tray until the gel has solidified. This will take 10 to 20
minutes. It will appear cloudy, or opaque, when ready to use.
Carefully remove the comb from the solidified gel.
Remove the tape from the edges of the gel tray.
Place the tray into the DNA electrophoresis chamber so that the sample wells are at
the black (cathode) end of the base. DNA samples will migrate towards the red
(anode) end of the chamber during electrophoresis.
S