The Teenage Romance Riddle: A Crime of the Heart?
Written by Terri Hamstra
A. Intended audience/previous knowledge
This lesson was originally written for middle school students, although I’ve done the fingerprint and hair sections (not
the DNA gel electrophoresis) with 5th graders. My 15 year old daughter and 11 year old son helped me write this. This
lesson could be used for freshman high school students. Very little background knowledge is needed, but some
knowledge of the cell, uniqueness of each person’s DNA, characteristics of DNA, and a little about charges (opposites
attract) is helpful but can be done along with the lesson. The vast majority of students have seen crime shows on TV
so are already somewhat familiar with the role that science plays in helping investigators solve crimes.
This lesson can be easily changed so that the evidence points toward “guilt”, or so that the evidence points toward
“innocence”. With several classes, you can change the results so that not all classes are the same (some have “guilty”
evidence, some have “innocent” evidence. Interestingly, I’ve found that some students are disappointed if the
evidence points toward innocence.
B. Learning Objectives for Students
1. To learn a simple DNA extraction technique
2. To learn to work in groups of 3-4, and problem solve together
3. To learn about how to identify hair from four different species and compare to hair from a crime scene
4. To learn about fingerprints, how to make their own, identify their own, and identify fingerprints from a
crime scene
5. To learn about DNA and gel electrophoresis and actually perform it
6. To put all the evidence together to help solve a “crime”; also to realize that physical evidence is not proof,
but evidence pointing toward guilt or innocence
C. Materials
DNA extraction:
See Kiwi Fruit DNA extraction
Crime scene (“Evidence” bags are not crucial but help set the stage)
1. 1 popcorn bag in large Ziploc bag (“evidence”)
2. 1 teenage boy’s jacket (“evidence”)
3. 1 soda cup with lid with chewed up gum on the lid in Ziploc bag (“evidence”)
4. 1 straw in Ziploc bag (“evidence”)
5. 1 Chapstick in Ziploc bag (“evidence”)
6. 1 long dark hair with hair follicle in Ziploc bag (“evidence”)
7. handouts for hair analysis (SEM photos of known hair and crime scene hair to match) – 1 per group
8. pencils
9. scratch paper
10. invisible tape – 1 for every 2 students or at least 1 for every 4 students or there is too much “down time”
11. blank fingerprint cards – 1 per student
12. 3 X 5 index cards to practice IDing fingerprints, cut in half – 1 card for every 2 students
13. set of known fingerprints, and from crime scene – 1 set per group
14. gel electrophoresis equipment, agarose, DNA samples, etc for the DNA section
15. Teenage Romance Riddle Student Worksheet
You use some or all of this activity.
D. Logistics/timeframe
The DNA extraction from cheek cells can be done in even a short class period (e.g. 40 minutes) but this part can be
skipped because it is not crucial for solving the “crime”. For the “crime”, I have been able to do both the hair and
fingerprints in about 1 hour 20 minutes with a group with no background, and the DNA gel electrophoresis in 1 hour 10
minutes with the kids pouring their own gels but that was really pushing it. The DNA part can be done in less than an hour
if you pour the gels. I think it would be best to have at least 3 class days, 4 or 5 ideally.
E. State Standards
I teach mostly at the community college level so I know little about state standards. I substitute and volunteer for middle
and high school, and I’ve been told this lesson meets standards for genetics and inquiry based learning.
F. Background (more than you need to know)
Hair: Hair can be valuable evidence because, since hairs can be transferred during physical contact, their presence
can associate a suspect to a victim or a suspect/victim to a crime scene. The first step in examining a hair from a
crime scene is to determine whether the hair originated from an animal or a human being. If the hair originated from
an animal, it is possible to further identify it to a particular type of animal. Although certain hairs can be attributed
to species, it is not possible to identify hairs to a specific animal to the exclusion of other similar animals. An
example of this occurs when dog hairs can be associated to a particular breed but cannot be identified to a specific
dog within that breed. If it is a human hair, it may be possible to narrow down the possibilities of whose hair it is.
The basic morphology of human hairs is shared by each individual in the population, but the arrangement,
distribution, and appearance of individual light microscopic characteristics within different regions of hair routinely
allow a skilled hair examiner to differentiate hairs between individuals. We cannot acquire these skills in the school
classroom, so instead we will use SEM photos of hairs magnified 1000X and identify hairs to species. However,
students should be told that SEM photos are not how hairs are identified in real life crime labs.
Fingerprints: Fingerprints are still used and considered one of the best types of physical evidence because no two people,
not even identical twins, have the same fingerprints. The identical twin issue is a good one to launch a discussion of nature
and nurture, genes and environment. The identical twins fingerprints have a genetic base, but the intrauterine environment
will largely determine the fingerprint patterns. Fingerprints are formed by about the 13th week gestation, and everyone’s
fingertips are affected by what he/she touches in utero during fingertip development. Fingerprints are made by the minute
ridge formations or patterns found on fingertips. The patterns of fingerprints do not change throughout life, although the
ridges can become worn down, and scars and creases can be acquired. The first time fingerprints were used to identify a
person in the U.S. was in 1902, although Mark Twain wrote a story about fingerprints being used to identify a murderer in
1883. The method had been used for personal identification perhaps in ancient times as thumbprints have been found on
clay Chinese seals. We will use the pencil and tape technique (invisible tape works better than transparent tape and is
worth the slight extra expense), as it is much cheaper and cleaner than using ink, and cleaner than using charcoal, and
gives a good fingerprint.
DNA: DNA analysis has been used in forensic science since the 1980’s, and used for the first time in a trial in 1983. At
first a method called Restriction Fragment Length Polymorphism (RFLP) was used, which took a fairly large (quartersized) sample of e.g., blood. With the advent of the polymerase chain reaction, or PCR, a sample the size of a pinhead can
now be used. Since 99.9% of everyone’s DNA is identical, the locations, or loci, of variable regions of DNA needed to be
identified in order to differentiate between people. By 1998, the FBI had determined 13 different highly variable loci of
Short Tandem Repeats (STR’s), which could be used to construct a DNA profile, or DNA fingerprint. These STR’s, all on
nonfunctional DNA, are composed of 2-7 base pairs, and taken together are unique to each human being (except identical
twins). For example, the minimum discrimination power of the 13 loci for Caucasians is 1 in 150 billion, several times the
world’s population. At the Department of Public Safety Crime Lab in Phoenix, AZ, which follows FBI protocols, each
sample is amplified by PCR a total of 28 cycles, then run on polyacrylamide gel. While it used to take about 3 months to
produce a DNA profile using RFLP, it only takes 1-3 weeks to obtain a DNA profile using PCR. However, DNA profiles
often take much longer due to the backlog of samples at crime labs.
We will use dyes that simulate DNA and form two bands per person (1 from each parent) with gel electrophoresis. The
dyes are inexpensive, easy to use, you don’t have to stain the gel at the end, and you get the results quickly. However, you
must read the gels the same day you run them (this can be a problem for short class periods) or the dyes will diffuse and
you won’t have any bands by the next day.
G. Chronology of Lesson Plan in ideal world (5 days total):
Day 1 –DNA extraction (you will need to prep lab ahead of time). Students work in pairs, each student gets to
spool DNA.
Day 2 – Identifying 4 different types of hair to species using SEM photos (work in groups of 3-4). Introduce story
and crime scene.
Identify hair from jacket to species, answer questions, discuss implications. (I have chosen the cat hair as
the hair at the crime scene, but you can choose a different species if you wish.)
Day 3 – Have students (pairs) make their own fingerprints on FBI fingerprint cards. Have each place a fingerprint
on an index card with their name and which finger on the back and trade with other pairs and try to
identify. Distribute copies of fingerprints of “suspects” and have them identify fingerprints from crime
scene evidence, e.g., popcorn bag and chapstick. Talk about as a class or wait until the next day.
Day 4 – Discuss fingerprints, briefly explain gel electrophoresis, fill out first part of form on DNA, discuss as a
class, discuss known DNA samples, present 4 different sources of DNA evidence from crime scene, have
groups of 3-4 students pick which evidence they want, then tell them there’s a “2 for 1 sale” and they can
pick another crime scene sample, write down map of knowns and crime scene evidence samples (5 total).
Day 5 – Perform gel electrophoresis. It’s up to you whether you pour the gels or have students do it or have them
do it at the end of class for the next class. Try to have students keep results of their gel to themselves so
you don’t get the “one right answer” effect. Have students read and measure gels and answer questions on
handout. If desired, give last paragraph as homework assignment. Encourage good science and creativity
and good grammar and spelling. Here is the key to the samples and two options:
Known sample 1= Daniel
Known sample 2= Renee
These are the same no matter what.
Known sample 3= Brittany
You can tailor the unknowns. Examples:
Evidence pointing toward “guilt” example
A. Unknown Gum
Daniel (1)
B. Unknown straw
Mix of Daniel & Brittany (1 & 3)
C. Unknown Chapstick Brittany (3)
D. Unknown hair
Brittany (3)
A. Unknown Gum
Evidence pointing toward “innocence”
Daniel (1)
Mix of Daniel & Renee (1 & 2)
Renee (2)
Renee (2)
Evidence pointing toward “guilt” example
Mix of Daniel & Brittany (1 & 3) (provokes good “yuck” reaction from students)
H. Assessment:
I assess this by the worksheets, participation, and especially by the last paragraph they write as both science and creative
writing.
I. Resources
1. Hair (background and using light microscope which I was not good at AT ALL)
US Dept of Justice: FBI
Hairs, Fibers, Crime, and Evidence
http://www.fbi.gov/hq/lab/fsc/backissu/july2000/deedric1.htm#Hair%20Evidence
Great examples of light microscope slides of human, dog, cat, and deer hair:
http://dsc.discovery.com/fansites/onthecase/hair/photo.html
Forensics Science, University of Colorado at Boulder
http://www.fbi.gov/hq/lab/fsc/backissu/july2000/deedric1.htm#Hair%20Evidence
Lesson plan on using hair at a crime scene – very detailed – high school or college
http://library.thinkquest.org/04oct/00206/lesson.htm#hair
Animal Hair Set from Boreal Labs ($8.50) (dog, cat, rabbit, rat)
http://www.sciencekit.com/category.asp_Q_c_E_749858
Discoveryschool.com Forensic Detectives On-line lesson plan for Grades 6-8
http://school.discovery.com/lessonplans/programs/whodidit/ (fingerprints, hair, thread)
2. Fingerprints
Who did it? Lesson plan using fingerprints to solve a crime in the classroom – stolen exams (nicely done)
http://www.teachersfirst.com/lessons/forensics/finger-lesn.html
Fingerprint patterns:
http://www.reachoutmichigan.org/funexperiments/agesubject/lessons/handouts/print_patterns.html
Fingerprinting: A Lesson on Classification: (late elementary or middle school – recommends using pencil
graphite for fingerprints)
http://www.reachoutmichigan.org/funexperiments/agesubject/lessons/prints.html
FBI’s Intro to Fingerprints:
http://www.fbi.gov/hq/cjisd/ident.pdf
Fingerprint lesson plan (includes short Powerpoint presentation):
http://www.create.cett.msstate.edu/create/classroom/lplan_view.asp?articleID=89#handout2
Fingerprint lesson plan (grades 3-8) (National standards are given.):
http://www.educationworld.com/a_lesson/03/lp299-01.shtml
Phenotype v. genotype: Why identical twins have different fingerprints (short article)
http://forensic-evidence.com/site/ID/ID_Twins.html
Journal article regarding fingerprints of identical twins from 2002 (for the HIGHLY motivated):
..\ID twin fingerprint journal article.pdf
3. More complex Crime Scenes:
Very detailed – includes bloody footprint at crime scene – not for younger kids
http://library.thinkquest.org/04oct/00206/lesson.htm#hair
4. General
http://www.fbi.gov/kids/k5th/kidsk5th.htm (FBI Kids Page for K-5)
http://www.fbi.gov/kids/6th12th/investigates/investigation.htm (FBI Kids Page for Grades 6-12)