3/14/2014
3.13.14
Bell work
Objectives:
• Explain how the DNA
bands were separated
when we ran our gels
on Monday.
• I will:
▫ Finish the PCR
Forensics lab
▫ Write an argument for
or against various uses
of DNA.
Due TODAY!:
• Turn in your composition book:
▫ PCR Forensics Lab:- total of 75pts
 Pre-lab question (10 questions) -20pts
 Drawing (timeline) with labels - 10 points
 Lab discussion questions (9 questions) – 25 pts
 Final results drawing, with labels and
measurements (15 pts)
 Results and discussion questions (5 questions)25pts
Results and Discussion Questions
• 1. Examine your stained gel on a light box or overhead
projector. Which suspects' DNA matches the evidence
DNA?
• 2. Compare your gel with the ideal gel photo provided by
your instructor. How can you account for differences in
separation and band intensity between your gel and the
ideal gel?
• 3. How would it affect the spread of the bands if a gel of
increased concentration were used?
• 4. If the two suspects had been identical twins, how
would it have influenced the results?
• 5. If you forgot to use a clean pipette, pipette tip, or other
loading apparatus for every sample that you loaded, how
would this affect your results from one lane to the next?
Lab Discussion Questions
Ideal Gel:
Compare your
gel to this one!
1. What is DNA and what does it do?
What’s going on?
2. What are some characteristics or properties of DNA?
5. What is the function of each of the following in gel
electrophoresis of DNA?
• Agarose gel:
▫ The agarose gel provides a matrix with pores to
allow molecules to travel through and be sorted by
size.
3. How can we take advantage of these properties to help
us figure out whose DNA was at the crime scene?
• Electric current:
4. What tricks can we use to see DNA?
• "Wells" in the gel:
▫ The electric current is the force that causes the
negatively charged DNA molecules to more toward
the positive pole.
▫ The wells are the "starting gates" for the DNA
molecules to be loaded into before starting the
"race".
1
3/14/2014
9. Examine the diagram of an agarose gel and answer the following
questions.
What’s going on?
• 6. Toward which pole (positive or negative) does DNA
migrate when electric current is run through the gel?
______
positive Why do the DNA molecules move toward this
pole?
A.
B.
C.
▫ The DNA molecules are negatively charged
(opposite charges attract one another).
• 7. What would happen to the DNA fragments if you
forgot to turn the current off?
▫ The DNA fragments would keep on running
through the gel until they ran off the end.
• 8. Describe how different sized DNA fragments are
separated by the gel matrix.
▫ Longer DNA fragments take longer to work their
way through the pores of the gel matrix, they don't
travel as far through the gel as the shorter
fragments in the same amount of time.
What do the bands in the drawing of the agarose gel represent?
Many DNA fragments which are the same size
Which band(s) traveled slowest?
▫
The bands nearest the wells (containing the longest DNA
fragments) traveled the slowest. (Band #1)
Which band(s) traveled fastest?
▫
The bands farthest from the wells (containing the shortest DNA
fragments) traveled the fastest.
Bands #10.
On the above drawing, label the positive and negative ends of the gel.
▫
The negative pole is located closest to the wells. The positive pole is
located furthest from the wells. SEE DIAGRAM
How many bands are shared in common by all of the individuals?
▫
3 (Bands #1, #4 and #9)
▫
D.
E.
F.
Are there any bands which are unique to only one individual?
▫
G.
▫
yes__
If so, which one?
Bands #6 (sample C) and #10 (sample A).
Sample Gel Electrophoresis Results:
Get out a separate sheet of paper, title it: USES OF DNA
Uses of DNA
• DNA Evidence & the FBI database (2:16)
▫ Video
1. Currently violent convicted felons’ DNA
samples are stored in CODIS. Should this
database be expanded to include ALL
convicted felons (even for “non-violent”
offenses)? Why or Why not? In no less than a
paragraph, defend your answer. Provide
evidence (examples) to support your answer.
Uses of DNA
• Link for Missing Kids (7:32)
▫ Video
▫ http://www.youtube.com/watch?v=5p-V-rnPaqw
2. Everyone, when they are born, should be required
to give a DNA sample to be on file with the
government for law enforcement to use in case of
emergency.
▫
In no less than a paragraph, answer the following: Do you agree
with this statement. Why or Why not? Provide evidence (examples
from your life, the video, other sources) to support your answer.
3. Would it be ok to put every day citizen’s DNA into CODIS as well?
Why?
2
3/14/2014
Closing Question
• Do you agree or disagree with the statement that
DNA should be collected from every baby and
stored by the government for use in case of
emergency? What could change your mind?
3