Title: You ARE Unique! Genetic Diversity and DNA Profiling
Developer: Elise Walck-Shannon
Date: Spring 2013
Topics: Genetics, Molecular Biology, Information Flow, Science and Society
Level: This module was developed for an introductory Biology course (Bio 100) but
could be adapted for an upper-level Genetics course or Molecular Techniques course
quite easily. With some detail removed, this module may also be applicable to high
school.
Overview: This activity uses DNA profiling to introduce students to the concept of
genetic diversity within the human population. Specifically, students will compare DNA
profiles from crime scene evidence to three suspects, calculate the probability of seeing
a match by chance, and decide whether a suspect is guilty, given the context of the
evidence.
Our course was set up as an hour long lecture followed immediately by an hour long
discussion activity. The following Learning Goals and Learning Outcomes are organized
by lecture and discussion (or both). For the module to be successful, you will likely need
to spend some time covering the “lecture” learning goals.
Learning Goals:
1. Students will understand basic genetic terminology and the central dogma of
molecular biology.
2. Students will know that new alleles can arise by errors in replication (mutation).
3. Students will appreciate that DNA fingerprinting requires us to assume that allele
frequencies are the same over multiple generations (Hardy-Weinberg Equilibrium).
4. Students should understand that alleles on separate chromosomes are inherited
independently; therefore, genotype frequencies for loci on separate chromosomes can
be multiplied together.
5. Students will comprehend the basic technique of DNA fingerprinting, and be able to
use this knowledge to critically examine real cases.
Learning Outcomes:
For Goal 1
1. Students will be able to define a locus, allele, allele frequency, genotype and
phenotype. They will also be able to define a short tandem repeat (STR, the type
of DNA sequence used for DNA profiling).
2. Students will be able to order the processes of transcription and translation, and
decide whether certain DNA sequences (the STR loci used in DNA fingerprinting)
are likely to undergo one or both of these processes.
For Goal 2
1. Students will comprehend that repetitive sequences are especially vulnerable to
copying errors, and thus have high levels of diversity in a population.
For Goal 3
1. Students will use Hardy-Weinberg Equilibrium assumptions to calculate genotype
frequencies, when given allele frequencies.
For Goal 4
1. Students will calculate the probability of a random match (known as the Random
Match Probability, RMP) using multi-locus genotyping results (“DNA profiles”).
2. Students will decide if finding a hit in a database can incriminate “beyond a
reasonable doubt”.
For Goal 5
1. Students will decide if they believe the DNA match from a database hit is enough
to convict him/her for murder (John Puckett case).
2. Students will be able to analyze an electrophoretogram and share their
interpretation with the rest of the class. They will also be able to weigh the
preponderance of evidence (Amanda Knox case).
3. Students will come up with potential short-comings of DNA evidence, and weigh
the pros and cons of DNA profile availability.
Description:
This module is designed to get students excited about genetic diversity, using the highly
publicized example of DNA profiling. This was the second lecture of the semester for a
second-semester freshman course. So, considerable time was spent reviewing basic
genetics. During lecture, the students were reintroduced to basic genetics and
population genetics, then given an overview of the DNA Profiling technique and
corresponding calculations. To maintain student interest, this was done in context of an
actual case, where John Puckket was convicted for a murder, even with an incomplete
DNA profile1 (see powerpoint in Supplemental Materials for more information).
During discussion, we had the students role play as both forensic lab technicians (first
25 min.) and jury members (second 25 min.) in the trial that investigated the murder of
Meredith Kercher. This case was highly publicized due to the conviction—which was
later overturned—of the American student, Amanda Knox. For more details, see
Instructor Materials below.
The idea was to get students engaged using real cases that they may have already
heard about. One suggestion for future execution of this module would be to insert more
discussion about the societal implications of DNA Profiling—especially with current
legislation and rules that have broadened the number of people included in DNA
databases.
Activity Timeline:
I. BEFORE LECTURE ASSIGNMENT (~10 minutes)
This involves a short reading and multiple choice quiz to assess students’ prior
knowledge. We administered the quiz online. See “Before Lecture Assignment” section
of the Student/Instructor Packets for the questions and readings.
1
http://www.washingtonmonthly.com/features/2010/1003.bobelian.html
II. LECTURE (50 minutes)
Also see “Class Notes” section of the Student/Instructor Packets and the powerpoint file
in Supplementary Information.
Minutes
Brief Description
0-2
2-7
Introduce Self
Introduce the John Puckket Case
(revealing only the evidence
presented to the jury)
Corresponding Active Learning Exercises
Goal
N/A
Hook and #5
Have students vote for a verdict,
given only the information they
were given so far.
7-10
Overview of DNA Fingerprinting
#5
10-15
Transition to basic genetics.
Introduction to genetic
terminology and the central
dogma.
#1
Clicker questions that apply this
knowledge to the STR loci used
in DNA fingerprinting.
New alleles come from errors in
replication. Genetic diversity at
STRs is the basis of DNA
fingerprinting.
Diversity can be quantified by
measuring the frequency of
alleles. Hardy-Weinberg
Equilibrium posits that allele
frequencies are constant from
generation to generation.
Review of independent
assortment during meiosis and
probability of mutually exclusive
events.
#2
Activity that instills difficulty of
replicating repetitive DNA.
#3
Clicker T/F Question: HWE is a
realistic rule that predicts allele
frequencies over many
generations.
#4
Think-pair-share: Predict the
results of an electrophoretogram
for a parent and child. Decide if
a given example illustrates a
parent-child relationship.
35-40
Calculate the random match
probability (RMP) for John
Puckett.
#4 and #5
Ask for response: Would a
complete DNA profile give a
higher or lower RMP?
40-43
Introduce DNA databases.
#4 and #5
43-45
Revisit John Puckett case
#5
45-50
Only if extra time: Introduce other
applications of DNA
fingerprinting: Innocence Project,
World Trade Center ID, Dog
Poop2
#5
Students calculate the number of
random hits expected for John
Puckett.
Have students revote for a
verdict to convict John Puckett.
Ask students to reflect on
voluntary donation of their DNA
sample.
15-20
20-25
25-35
2
http://www.cnn.com/2011/US/06/27/new.hampshire.dog.dna/index.html
III. DISCUSSION ACTIVITY (50 minutes)
Minute
1-5
Description
Short introduction to the Meredith Kercher case
(either verbal or short video)
Learning Outcome
N/A
5-8
Have students split up into five groups.
Distribute unique DNA evidence to each group.
N/A
8-25
Students will analyze a DNA profile relative to
reference samples of suspects and answer a
series of questions as a group. They will also
prepare three to four sentence conclusion to
share with the rest of the class.
Each group will select one member to testify their
conclusion based on the DNA evidence. The
remaining students will play the role of a jury.
Discussion of evidence presented, as if each
were a jury member.
Vote on the guilt of each suspect.
From class: Calculate RMP
25-32
32-45
45-50
Communication of results
Weighing evidence
Final Vote and short video of actual outcome.
IV. SUMMATIVE ASSESSMENT (~30 minutes)
This was administered online and is a mixture of multiple choice and free response
questions. See “Summative Assessment” section of Student/Instructor Packets for
questions and a key.
Materials:
Lecture
Clickers (nice to have, but not required)
Projector and Laptop
OPTIONAL: “Genetic Diversity Class Notes” (See Student/Instructor Packet) 1/student
Discussion Activity
Projector and Laptop with Internet Connection to play clips from NPR and Associated
Press
Handouts – both in “Discussion Activity” section of Student/Instructor Packets.
1. Discussion Handout - there are five unique handouts (each student should get a
handout, and students within the same group should get the same handout)
2. Reference Sample Handout – contains DNA Profiles for the victim, suspects,
and population allele frequencies for the calculations (same for all students)
Instructor Materials:
Lecture
See powerpoint entitled “Genetic Diversity and DNA Profiling” and “In Class Notes”
section of Student/Instructor Packets.
Discussion Activity
We will have the students role play as both forensic lab technicians (first 25 min.) and
jury members in the trial that investigated the murder of Meredith Kercher (second 25
min.). To introduce the students to the case, we will open with video from the
Associated Press, which briefly explains the trial and three prime suspects:
https://www.youtube.com/watch?v=ogHCnfEyjeQ
or
https://www.youtube.com/watch?v=dIOF1cS2RNI
Order of Events:
(PLEASE FEEL FREE TO CHANGE UP THE ORDER OF EVENTS AS YOU SEE FIT. Some of the
instructors had the students go through the DNA evidence BEFORE they revealed the
details of the case, which should still obtain the desired outcome.)
LEAST DIFFICULT
Group 1 will analyze the tip of the knife found in a kitchen drawer at the crime scene.
The DNA is noticeably weaker than the reference samples. There was no blood
found on the knife tip.
MOST DIFFICULT
1. For the first five minutes, we will explain to them that there were three suspects
in the original case, which were all convicted for the murder of Meredith Kercher:
(1) her roommate Amanda Knox, (2) Raffaele Sollecito (Amanda’s boyfriend),
and (3) Rudy Guede (who had no known connection to Meredith). Amanda Knox
has issued an appeal of this verdict, and they are part of a team of scientists in
charge of re-analyzing the DNA evidence.
2. The students will split up into five groups.
3. Each group will receive a different piece of DNA evidence, but all groups will
receive reference DNA profiles for all three of the suspects and the victim, along
with a table of allele frequencies.
4. Students will spend ~15 min. answering questions about the DNA profiles.
Students will: 1. decide which suspect’s DNA matches the DNA found on the
sample, 2. calculate the random match probability for the suspect, 3. understand
any special circumstances for their particular piece of evidence, and 4. decide
whether that match is indicative of guilt.
Group 3 will analyze DNA from Meredith Kercher’s bra. This is a mixture of the
victim’s (major contributor) and suspect’s (minor contributor) DNA. The DNA was not
collected from the crime scene for over a month, and an American scientist—Greg
Hampikian—was able to show that the suspect’s could have been due to
contamination.
Group 2 will analyze the handle of a knife found in a kitchen drawer at the crime
scene. The DNA is noticeably weaker than the reference samples.
MODERATELY
DIFFICULT
Group 4 will analyze DNA from a bloody handprint found on a pillow near the victim.
The sample contains a mixture of the victim’s and a suspect’s DNA.
Group 5 will analyze DNA found inside the victim. The sample contains a mixture of
the victim’s and a suspect’s DNA.
For your reference, a table below summarizes the results:
Group
Piece of
Suspects
Relative
DNA mixed
Number
Evidence
Importance
with Victim?
Match to
Eventual
Outcome
1
Knife Tip
Victim
N/A
No blood on
No
tip
2
Knife handle Amanda
Acquitted
Could have
No
Knox
been used for
other
purposes
3
Bra
Raffaele
Acquitted
Not recovered Yes
Sollecito
for 47 days.
His DNA was
not found
anywhere else
on the bra.
4
Pillow near
Rudy Guede Convicted
Yes
Victim
5
Rape Kit
Rudy Guede Convicted
Yes
(Please note that for privacy reasons, these chromatograms are made-up; they are not
the actual profiles for the persons in question.)
5. Each group will select a spokesperson, who will “testify” their conclusions to the
rest of the class.
6. Have the spokesperson for each group sit at the table in the front of the room,
and the remainder of students face forward. Emphasize that the rest of the class
is now playing the role of a jury.
7. The spokespeople will present their evidence. (Please intervene as you see fit—
you could even play the role of a judge if you want to be crazy!)
8. After conclusions from all groups have been shared, you can allow the jury to
discuss their verdict.
9. Take a poll from the class for the conviction of each suspect.
10. Present the actual results of the appeal:
Either state in words or play the following audio clip (the first 1:02 min. are most
important):
http://www.npr.org/2011/10/03/141019164/italian-appeals-court-releases-amanda-knox
From “All Things Considered” on NPR.
Intended Answers:
In the Student Packet, please find the complete worksheets (“Discussion Activity”
section) and in the Instructor Packet, please find the answers (“Discussion Activity”
section).
If you want to learn more:
CNN Wire Staff. CNN Justice. “The case against Amanda Knox.”
http://www.cnn.com/2011/09/28/justice/italy-knox-evidence/index.html
Geddes, Linda. NewScientist. “Knox murder trial evidence ‘flawed’, say DNA experts.”
http://www.newscientist.com/article/dn18215-knox-murder-trial-evidence-flawed-saydna-experts.html
Greenhill, Sam. The Daily Mail. “The Meredith Kercher murder lies… and the questions
that have never been answered.” http://www.dailymail.co.uk/news/article2045336/Meredith-Kercher-crime-scene-Questions-answered.html#axzz2JlDEBQrf
Hampikian, Greg. NPR. “Analysing the Evidence on DNA.”
http://www.npr.org/2012/09/28/161955789/analysing-the-evidence-on-dna
Niiler, Eric. Discovery News. “How Dodgy DNA Freed Amanda Knox.”
http://news.discovery.com/human/genetics/dna-evidence-knox-trial-111004.htm
Tuck, Kathleen. Boise State University. “Hampikian, Idaho Innocence Project at Center
of Amanda Knox Appeal.” http://news.boisestate.edu/update/2011/05/11/hampikianidaho-innocence-project-at-center-of-amanda-knox-appeal/
Student Materials:
Please find a single document “Genetic Diversity and DNA Profiling Student Packet”
(and the corresponding expected answers in “Genetic Diversity and DNA Profiling
Instructor Packet”). Both documents have a similar table of contents (below), but the
“Student” version has blank spaces, while the “Instructor” version has intended answers
and rubrics.
Table of Contents
Before Lecture Assignment ..................................................................................................2-3
In Class Notes ........................................................................................................................4-7
Discussion Activity ..............................................................................................................8-18
Group 1: The knife tip ...........................................................................................................8-9
Group 2: The knife handle ...............................................................................................10-11
Group 3: Meredith’s Bra Clasp.........................................................................................12-13
Group 4: Bloody Handprint ..............................................................................................14-15
Group 5: Rape Kit ............................................................................................................16-17
Reference Samples ..........................................................................................................18-19
Summative Assessment Questions ..................................................................................20-21
Supplementary Materials:
1. Before Class Reading: “How DNA Profiling Works”
2. “Genetic Diversity and DNA Profiling” Lecture Powerpoint