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Lost Tribes of Israel
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Classroom Activity
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Objective
To understand the issues involved with using DNA evidence in a
courtroom trial.
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copy of "Did the Dog Do It?" student handout (HTML)
- Additional reference sources
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Organize students into two juries of approximately 12 students
each. Distribute copies of the "Did the Dog Do It?" student
handout to each student.
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Tell students they will be trying a case involving a man bitten
by a dog. A pit bull named Buddy is accused of biting a
38-year-old man named Taylor. The pit bull's owner, Sam, says
his dog didn't do it. Taylor claims that DNA taken from saliva
on a towel he used to clean the bite matches Buddy's DNA.
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Have students read the evidence that has come out during the
trial and discuss what they can infer from this evidence.
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Tell students to brainstorm other questions they would like to
have answered about how DNA fingerprinting works. Instruct
students to use additional resources to research their answers.
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Have students consider what other questions are important in
deciding this case, such as how the evidence was collected and
processed.
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Based on what students learn from their research and the other
issues they have considered, have them vote and decide whether
they think the accused canine is innocent or guilty.
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Have each jury report its verdict and explain how it reached its
decisions, including what resources it used to come to its
conclusions. If either jury is hung, discuss why and whether
additional information would have helped them reach a verdict.
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Discuss with students the differences in how the DNA is used in
the program and how it is used in this activity.
(The DNA evidence used in the program looks at a set of
unique changes on the Y chromosome over time; however, those
changes may not be present in Jewish males who are descendants
of the Cohanim, or may be present in Jewish males who are not
descendants of the Cohanim. The DNA markers in this activity
are used to determine the probability of a match to a specific
individual dog, as well to exclude dogs who do not have the
match.)
DNA evidence cannot conclusively prove that a person, or in this
case, a dog, committed a crime. What it can do is show the
probability of someone having the same DNA match. The probability
given for a DNA match states the probability of finding a particular
profile by chance in a population. For example, if the probability
of 1 in 10,000 were given for a match to the dog's DNA, then in a
city of 5,000,000 dogs, there would be 500 dogs that could match
this profile purely by chance. Jurors would then need to decide
whether the dog is innocent given this probability.
DNA evidence can also rule out people from being considered as
suspects when no match exists.
Every organism's DNA is composed of strings of four different
nucleotides: G(uanine), C(ytosine), A(denine), and T(hymine). These
strings of nucleotides are connected to one another by nucleotide
pairing (G-C and A-T) to form the two-stranded DNA molecule that
makes up the chromosome. For the most part, the order—or
sequence—of these base pairs is very similar from one
individual to another. However, there are regions of DNA that are
highly variable in length and/or sequence and therefore are
different from individual to individual (except in identical twins
whose DNA is identical). These variable regions of DNA are typically
used in DNA fingerprinting.
A DNA fingerprint is made by taking a sample of DNA—which can
be taken from nuclear or mitochondrial DNA found in almost every
living cell—making copies of the extracted DNA, and isolating
certain known base pair sequences. Since the fragment lengths
starting with these known sequences differ in every person, they can
be used to help determine identity. A DNA fingerprint looks at only
a small number of base pair sequences contained in a person's total
DNA. Nevertheless, the differences between the DNA in different
people is such that even these small number of sequences can
eliminate a large majority of other people as a suspect.
Other issues students might consider:
How was the DNA collected and processed? Could the evidence have
been contaminated with DNA from another source? How much DNA was
available for testing? How many different DNA segments were
analyzed? Are any other neighborhood pit bulls from the same litter
as Buddy? Were the lab procedures conducted accurately? What were
the credentials of the expert who presented the DNA evidence? Was
the expert paid, and if so, how much?
Books
Journey to the Vanished City
by Tudor Parfitt, London: Hodder and Stoughton, 1992.
Delves deeper into the journey described in the program and includes
features such as a map of the route.
Articles
"Order in the Lab! As the judge sets a date for the Simpson trial,
lawyers wrangle over the DNA tests that could seal O.J.'s fate." by
Leon Jaroff, Time, 8 August 1994, 46.
Reviews different types of DNA processing techniques.
"The Priest's Chromosomes." by John Travis, Science News, 3
October 1998, 218-219.
Details the DNA analysis supporting the passing of a genetic marker
on the Y chromosome of Jewish priests from father to son.
Web Sites
NOVA Online—Lost Tribes of Israel
http://www.pbs.org/nova/israel/
Delves deeper into the program's content and themes, with features
such as articles, timelines, interviews, resource links, and more.
Includes an online activity on how to create a DNA fingerprint.
Launch date: Friday, February 18.
Basics of DNA Fingerprinting
http://www.biology.washington.edu/fingerprint/dnaintro.html
Explores what DNA fingerprinting is, how it is done, its
applications, and some of the problems with using it.
Blackett Family DNA Activity
http://www.biology.arizona.edu/human_bio/activities/blackett/introduction.html
Details the concepts and techniques behind DNA profiling,
interpreting DNA autoradiograms, and evaluating DNA profiles to
determine familial relationships.
The "Did the Dog Do It?" activity aligns with the following National
Science Education Standards:
Grades 5-8
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Science Standard F: Science in Personal and Social
Perspectives
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Science and technology in society
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Science influences society through its knowledge and world view.
Scientific knowledge and the procedures used by scientists
influence the way many individuals in society think about
themselves, others, and the environment. The effect of science
on society is neither entirely beneficial nor entirely
detrimental.
Grades 9-12
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Science Standard F: Science in Personal and Social
Perspectives
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Science and technology in local, national, and global
challenges
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Understanding basic concepts and principles of science and
technology should precede active debate about the economics,
policies, politics, and ethics of various science- and
technology-related challenges. However, understanding science
alone will not resolve local, national, or global challenges.
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