70
i n ut e s
e ss
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ACTIVIT Y OVERVIEW
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1–2
50 -m
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40
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Finding the Lost Children
V EST IGA
SUMMARY
Students investigate the use of DNA fingerprints as evidence in establishing family
relationships. They use DNA fingerprints to obtain additional evidence about the
identities of the lost children of John and Belinda and of Mai and Paul.
KEY CONCEPTS AND PROCESS SKILLS
1.
DNA fingerprinting is done by using enzymes to cut an individual’s DNA into
characteristic pieces, and then separating the pieces to generate the
individual’s unique DNA pattern, or “fingerprint.”
2.
Because each person’s DNA sequence differs at many locations, each
individual’s DNA fingerprint is unique.
3.
Because individual DNA fingerprints are unique, they provide strong evidence
regarding identity.
4.
Inheritance of chromosomes from parent to child makes DNA fingerprinting a
powerful tool for verifying biological relationships.
KEY VOCABULARY
chromosome
DNA fingerprinting
DNA
MATERIALS
For each pair of students
*
1
Student Sheet 70.1, “Children’s DNA Fingerprints”
1
scissors
*Not supplied in kit
Teacher’s Guide
D-213
Activity 70 • Finding the Lost Children
TEACHING SUMMARY
Getting Started
1.
The class discusses the use of DNA fingerprints as evidence of biological
relationships.
Doing the Activity
2.
Students compare fingerprints of the children in Samarra with those from the
two couples.
Follow-Up
3.
The class discusses the results and answers the Analysis Questions.
BACKGROUND INFORMATION
Applications of DNA Fingerprinting
DNA fingerprinting can be applied most easily in medical forensics, in particular to
implicate or exonerate suspects by determining whether DNA evidence gathered at
crime scenes matches their DNA. The previous activity had students explore the fingerprinting process itself; the main observation was that DNA fingerprints from two
different individuals look clearly different.
In this activity, the use of fingerprinting to connect children to biological parents is
explored. Because each parent donates half of his or her chromosomes to a child,
about half the DNA fingerprint bands should be traceable to one parent, the other half
to the other parent. (Similar reasoning is applied in paternity testing, a less appropriate issue for the classroom.)
Actual DNA fingerprints are usually assembled from approximately four to six marker regions of the DNA. The more markers tested, the lower the probability that a match
is due to coincidence rather than identity.
D-214
Science and Life Issues
Finding the Lost Children • Activity 70
TEACHING SUGGESTIONS
GETTING STARTED
Samarra have DNA fingerprints that suggest they
belong to one of the couples.
Distribute Student Sheet 70.1, “Children’s DNA Fingerprints,” and a pair of scissors to each student
1.
The class discusses the use of DNA
fingerprints as evidence of biological
relationships.
pair. Students should cut out the strips representing
the fingerprints of the eight children. Have them
cut along the sides of each strip, but keep the child’s
Discuss the Introduction, on page D-87 in the Stu-
number, for identification. (Some may want to look
dent Book, briefly to get a sense of how familiar stu-
at only the fingerprints of the children who remain
dents are with the use of DNA fingerprinting in
as possible candidates from the ABO blood typing
court cases. Emphasize that the technique is also
evidence. This is good thinking, and tells you they
used for research in anthropology, in evolutionary
are alert. Tell them to check the fingerprints of the
studies, and in identification of children.
other children anyway, as they can serve for com-
Remind students of the desire to identify the children; the lack of samples of their DNA from before
their separation from their families will make this
more difficult. Ask, If the DNA of a mother and her
child were tested, would you expect the fingerprints to be the same? Would you expect the prints
to have anything in common? Some students may
suggest that some of the bands will be the same
since a child inherits half of his or her chromosomes from each parent.
DOING THE ACTIVIT Y
parison of DNA from children who are clearly unrelated.) Step 4 provides more evidence about one of
the children. As it turns out, Belinda has a source of
DNA from her daughter—a lost tooth. This tooth
can be used as a source of DNA for an even more
direct identification of this child. (If Belinda were
supplying false evidence, the DNA from the tooth
would be highly unlikely to match with DNA from
any of the children in Samarra.)
FOLLOW–UP
3. The class discusses the results and answers
the Analysis Questions.
2. Students compare fingerprints of the
children in Samarra with those from the
Use the fingerprinting analysis to reinforce the fun-
two couples.
damental idea of inheritance of chromosomes. The
Have students follow the Procedure. Step 1 helps
students see that the child’s DNA fingerprint shares
bands in common with both parents. Each band in
the child corresponds to a band in either the father
bands of a child’s DNA fingerprint match with
approximately 50% of the bands from each parent,
since the child inherits 50% of his or her chromosomes from each parent.
or mother, while the unrelated child has a different
Identification of possible children is not as direct as
pattern altogether. The remaining steps have stu-
detective work in which, for example, an unknown
dents determine whether any of the children in
sample is matched to the right suspect. However,
Teacher’s Guide
D-215
Activity 70 • Finding the Lost Children
due to the relative rarity of mutations, it is reliable.
Based on the DNA fingerprints, Girl 3 and Boy
Point out that actual DNA fingerprinting relies on
6 are Belinda and John’s. The DNA fingerprint
several markers instead of the single marker inves-
obtained from a daughter’s tooth further con-
tigated in this activity. This ensures a very small
firms that Girl 3 is their daughter Serena.
probability of falsely positive matches. Students
c.
may ask about how mutation would affect the fin-
Which child or children are not likely to be
those of Mai and Paul?
gerprints. While a mutation might affect one or two
bands, it would not affect all of the bands in the
Children 1, 2, 3, 4, 5, 6, and 8 can be complete-
complete fingerprint developed by looking at sev-
ly ruled out. Children 1, 3, 5, 6, and 8 can be
eral markers.
ruled out based on their blood types (see Student Sheet 68.3, “Finding the Children of Mai
Analysis Question 2 can be used as an assessment of
and Paul”). The DNA fingerprint results con-
students’ ability to interpret the results of the DNA
firm this analysis. In addition, Girls 2 and 4 can
fingerprint investigation. Score it with the “Analyz-
be ruled out based on the DNA fingerprints.
ing and Interpreting Data” element of the D ESIGNING
AND
CONDUCTING INVESTIGATIONS (DCI) scoring guide.
d.
Which child or children are likely to be those of
Mai and Paul?
SUGGESTED ANSWERS
Boy 7 is very likely to be their son, due to the
TO ANALYSIS QUESTIONS
1.
close match between his DNA fingerprint and
bands on Mai’s and Paul’s DNA fingerprints.
Use DNA fingerprint evidence and the
However, they have not found their daughter.
blood type evidence from Activity 68, “Searching for
the Lost Children,” to explain each of the following:
a.
2.
Write a convincing statement about
DCI
aid
Which child or children are not likely to be
which of the eight children (if any) are the
those of Belinda and John?
children of Belinda and John, and which of the chil-
Blood group evidence, described on Student
Sheet 68.2, “Finding the Children of John and
Belinda,” showed that children 1, 4, 5, and 7 are
very unlikely to be Belinda and John’s. Their
DNA fingerprints confirm this; they do not
dren (if any) are the children of Mai and Paul. In
your statement, provide as much evidence as you
can to convince a judge that the biological children
of these parents have been found. Be sure to include
evidence from previous activities.
show significant numbers of bands corre-
A level 3 response is shown here:
sponding to Belinda’s and John’s. Based on the
Three of the eight children tested from Samar-
DNA fingerprinting, it is also possible to rule
ra are the children of the parents from Namelia.
out Girl 2 and Boy 8.
Two of them are Belinda and John’s. The blood
b.
Which child or children are likely to be those of
Belinda and John?
type data were useful for narrowing the pool of
possible children, but the conclusive evidence
comes from DNA fingerprints. The bands from
D-216
Science and Life Issues
Finding the Lost Children • Activity 70
two of the children (Girl 3 and Boy 6) can all be
ter provides more evidence that Girl 3 is their
matched to bands from either Belinda or John.
daughter Serena. One of the children (Boy 7) is
This close match to both parents would be very
the biological son of Mai and Paul. His DNA
unlikely unless they are related, because each
bands can all be matched to either Mai or Paul.
person’s DNA is unique. The evidence that Girl
3’s DNA pattern is identical to the DNA pattern
from the tooth from Belinda and John’s daugh-
(A level 4 response might discuss mutations or
the fact that each child has half the chromosome complement from each parent.)
Teacher’s Guide
D-217
Name
Date
Children’s DNA Fingerprints
Cut out these DNA fingerprints and use them to determine who could be the children
of John and Belinda or of Mai and Paul.
Girl 2
Girl 3
Girl 4
! Boy 5
Boy 6
Boy 7
Boy 8
©2001 The Regents of the University of California
! Girl 1
Science and Life Issues Student Sheet 70.1
D-219