Download 1 Searching for the Lost Children

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Searching for the Lost Children
V EST IGA
SUMMARY
Students are introduced to the problem of identifying people who cannot identify
themselves. They read a story of some children lost during a war. Although the story
is fictional, it is based on actual situations in recent times (see Activity 71, “Should
We?”). In this first of four activities about the “lost children,” students use blood
groups to narrow a pool of children who may belong to the parents in the story. In the
activities that follow, students use genetic fingerprinting to identify the children and
consider the ethical implications of situations similar to the story.
KEY CONCEPTS AND PROCESS SKILLS
1.
ABO blood group is determined by a single gene, but there are four blood
types determined by three alleles. O blood type is recessive, while A and B are
co-dominant.
2.
Blood types can be used as evidence about identity and about family
relationships.
3.
Blood typing can provide sufficient evidence to rule out relationships, but not
enough to prove relationships.
KEY VOCABULARY
allele
co-dominance
Teacher’s Guide
D-181
Activity 68 • Searching for the Lost Children
MATERIALS AND ADVANCE PREPARATION
For the teacher
1
Student Sheet 68.1 Key, “Guide to the Lost Children”
1
Student Sheet 68.2 Key, “Finding the Children of John and Belinda”
1
Student Sheet 68.3 Key, “Finding the Children of Mai and Paul”
For each student
1
Student Sheet 68.1, “Guide to the Lost Children”
1
Student Sheet 68.2, “Finding the Children of John and Belinda”
1
Student Sheet 68.3, “Finding the Children of Mai and Paul”
TEACHING SUMMARY
Getting Started
1.
Introduce the need for ways to identify people.
Doing the Activity
2.
Students read the scenario.
3.
Students use blood group information to narrow the search for the children.
Follow-Up
4.
The class discusses the results and answers the Analysis Questions.
BACKGROUND INFORMATION
Using Blood Groups to Test for Relationship
As is the case for identity testing, ABO blood groups and Rh factor can be used only
to rule out relationships as impossible (or extremely unlikely). They cannot be used
to prove relationships because they don’t provide enough identifying information.
Both depend on the presence of antigens on red blood cells. For more information on
the ABO blood groups, see Activity 66, “Patterns in Pedigrees.”
Rh factor
The Rh factor is a protein on the red blood cells of Rh-positive individuals (just as A
antigen and B antigen are). Rh-negative individuals do not have this protein. Rh-positive blood is dominant because one allele that causes production of the Rh factor is
sufficient to produce an Rh-positive individual. The Rh factor causes an immune
response when Rh-positive blood is given to an Rh-negative person. Rh factor is of
D-182
Science and Life Issues
Searching for the Lost Children • Activity 68
concern during pregnancies: an Rh-negative woman may make antibodies against the
blood of an Rh-positive fetus if blood from the fetus crosses the placenta into the
mother’s circulatory system. Since the immune response develops over time, it usually does not lead to problems until a second pregnancy with an Rh-positive fetus. In
the second pregnancy, the mother’s immune system may attack the fetus by using a
response induced by memory cells, with disastrous consequences. The antibodies can
attack the fetal blood and cause severe anemia that can produce illness, brain damage, or death of the fetus or newborn. Rh factor is routinely tested during pregnancy.
In cases when the mother is Rh-negative and the fetus is Rh-positive, the mother
receives injections to prevent her immune response to the Rh factor. If a woman does
develop antibodies, the fetus can be checked and sometimes must be delivered early
or receive transfusions while still in the uterus.
Teacher’s Guide
D-183
Searching for the Lost Children • Activity 68
TEACHING SUGGESTIONS
GETTING STARTED
1.
Introduce the need for ways to identify
people.
for their real parents. By the time the political situation was stable, the adoptive families were no
longer willing to give up the children, since they
had come to feel that the children were part of their
own families.
Emphasize the introduction of a new blood factor.
Explain to students that there are a number of situ-
Explain that Rh is another factor that is used, in
ations in which it is useful to have information that
addition to ABO blood type, for identification pur-
will allow individuals to be identified. Some of the
poses—it provides additional information. Empha-
most obvious cases are those that involve criminal
size that Rh positive is the dominant trait for this
investigations. Forensic science uses a number of
characteristic.
techniques to obtain evidence to implicate or exonerate suspects. Another familiar, though rare, example is of children switched in the hospital shortly
3.
Students use blood group information to
narrow the search for the children.
after birth. Ask students, What kinds of techniques
Students should follow the Procedure for the activ-
are used to identify people who either cannot or
ity on page D-80 in the Student Book. They will
will not identify themselves or to find out whether
need to have their copies of the Student Sheets for
a person was involved in a crime? Students are like-
this activity in order to begin. Student responses to
ly to suggest fingerprinting, and may also suggest
the Student Sheets can be scored with the U N D E R -
blood typing or DNA testing.
S TA N D I N G
Explain that in Activities 68 through 70, students
will have a chance to use evidence to identify children separated from their parents as a result of political conflict.
DOING THE ACTIVIT Y
2.
Students read the scenario.
Select students to read each paragraph of the Scenario, or simply tell the story of the lost children as
it is described. Children were abducted by soldiers
during a war and then taken in by a neighboring
community that vanquished the soldiers. If students ask why the children were not immediately
returned, suggest that for the first few years there
was too much fighting and that it wasn’t safe to look
C O N C E P T S (UC) scoring guide. You may
wish to help them with part of Student Sheet 68.1,
“Guide to the Lost Children,” and then allow them
to complete the work individually for assessment.
Completing Student Sheet 68.1
This sheet allows students to review their understanding of the possible alleles for different ABO
blood types and for Rh factor. You may wish to
allow students to work in pairs or their groups of
four to complete this Student Sheet. If they have
trouble with the Rh factor, remind them that Rh
positive is dominant. They can use any systematic
approach to symbols for the two alleles; positive
and negative signs or “R and r” are possibilities. Students should begin by filling in the possible alleles
for each trait listed for the four parents and eight
children. A key is provided for your convenience.
Teacher’s Guide
D-185
Activity 68 • Searching for the Lost Children
The completed Student Sheet can then be used as a
exclude certain individuals, but blood type alone is
reference as students continue to Procedure Step 3.
not sufficient for positive identification. Addition-
Completing Student Sheets 68.2 and 68.3
al types of evidence are needed. For example, the
blood group evidence does not rule out Girl 2 as a
Students can work in pairs or individually to com-
possible child of either couple, but it does not pro-
plete Student Sheet 68.2, “Finding the Children of
vide enough evidence to decide which couple’s
John and Belinda.” They will compare the blood
child she is (if either).
type and Rh factor of each child with those of John
and Belinda to see if the child’s blood type is possi-
SUGGESTED ANSWERS
ble for children of these two parents. Then students
TO ANALYSIS QUESTIONS
should compare the blood types of each child with
those of Mai and Paul on Student Sheet 68.3, “Find-
1.
How certain are you that some of the eight children
belong to Belinda and John or to Mai and Paul?
ing the Children of Mai and Paul.” Keys are provid-
At this point, you cannot be that certain based
ed for your convenience.
on the blood evidence. More information
Students should conclude that children 2, 3, 6, and
would be needed. The evidence so far can rule
8 might be John and Belinda’s, while children 2, 4,
out certain children, but many children exist,
and 7 might be Mai and Paul’s.
besides the ones identified in the activity, who
have the same blood types as the parents in this
FOLLOW–UP
4.
story. Blood types can prove that certain chil-
The class discusses the results and answers
dren are not John and Belinda’s or Mai and
the Analysis Questions.
Paul’s, but cannot prove that any particular
children are theirs. For example, Girl 2 could
Discuss the approaches students used to make their
belong to either family, or to any other parents
decisions. In any case where both parents have a
with similar blood types.
recessive trait, all children expressing the dominant
trait can be quickly excluded. Thus all Rh-positive
children can be ruled out as children of Mai and
Paul. In other cases, students may have needed to
work through a mental process or to make a Punnett square to determine the possible child traits.
For example, you may wish to have students complete a Punnett square to show why Boy 8 cannot
belong to Mai and Paul.
In discussing the Analysis Questions, bring out the
idea that blood typing can provide evidence to
D-186
Science and Life Issues
2.
What additional evidence would help you identify
the lost children?
Students may ask about birthmarks or other
identifying features, more evidence about the
early lives of the children, or whether they have
any memories. Some may also raise the idea of
fingerprints or DNA testing.
Guide to the Lost Children (Key)
Fill in the table below with the possible allele combination(s) for each person. This will help you to
complete Student Sheet 68.2.
Type A
= AA or AO
(A is dominant over O)
Type B
= BB or BO
(B is dominant over O)
Type AB
= AB
(A and B are co-dominant)
Type O
= OO
(O is recessive)
Rh+
= Rh+Rh+ or Rh+Rh-
(Rh+ is dominant)
Rh-
= Rh-Rh-
(Rh- is recessive)
Table 1: Parents
Blood Type and
Possible Alleles
Belinda
A AA or AO
John
O OO
Mai
Paul
Rh Factor and
Possible Alleles
Rh+ ++ or + -
AB AB
Rh+
Rh-
--
B BB or BO
Rh-
--
++ or + -
Table 2: Children
©2006 The Regents of the University of California
Blood Type and
Possible Alleles
Girl 1
AB AB
Girl 2
A AA or AO
Girl 3
O OO
Girl 4
B BB or BO
Boy 5
AB AB
Boy 6
A AA or AO
Boy 7
Boy 8
Rh Factor and
Possible Alleles
Rh+ ++ or + RhRh+
--
RhRh+
--
++ or + -
AB AB
Rh+
Rh-
--
O OO
Rh-
--
Science and Life Issues Student Sheet 68.1 Key
++ or + -
++ or + -
D-187
Finding the Children of John and Belinda (Key)
Child
Could be John and
Belinda’s? (yes or no) Reasoning
no
Belinda and John do not have any alleles for type B blood, so an AB
child cannot be theirs.
Girl 2
yes
Girl 2 has type A negative blood, which is compatible with A positive
and O positive parents. Getting an A allele from Belinda and an O
allele from John would account for her blood type. Since Rh-negative
blood is recessive, both Belinda and John could have given her a recessive allele.
Girl 3
yes
If Belinda has a recessive O allele, which is possible, their child could
receive O alleles from both parents and have type O blood. Since both
parents are Rh-positive, Girl 3 also has a compatible Rh factor.
Girl 4
no
Belinda and John do not have any alleles for type B blood, so a type B
girl cannot be their daughter.
Boy 5
no
Belinda and John do not have any alleles for type B blood, so an AB
child cannot be theirs.
Boy 6
yes
Belinda and John, who have type A and type O blood, can have a type
A child. They are both Rh-positive and can have an Rh-positive child.
Boy 7
no
Belinda and John do not have any alleles for type B blood, so an AB
child cannot be theirs.
Boy 8
yes
If Belinda has a recessive O allele, which is possible, their child could
receive O alleles from both parents and have type O blood. Since both
parents are Rh-positive, Boy 8 also has a compatible Rh factor.
©2006 The Regents of the University of California
Girl 1
Science and Life Issues Student Sheet 68.2 Key
D-189
Finding the Children of Mai and Paul (Key)
Child
Could be Mai and
Paul’s? (yes or no)
Girl 1
no
Since Rh-negative blood is recessive, Rh-negative parents are homozygous for the recessive allele. Thus, two Rh-negative parents cannot
have an Rh-positive child.
Girl 2
yes
Yes. Child has type A blood, which is possible if Paul carries an O
allele.
Girl 3
no
Child has type O blood, which means she cannot be Mai’s child since
Mai’s children must receive either an A or B allele. In addition, as
described for Girl 1, an Rh-positive child cannot be the biological child
of Mai and Paul.
Girl 4
yes
Type B blood in a child is possible for AB and B parents, and Girl 4 is
Rh-negative, as expected for all children of Mai and Paul.
Boy 5
no
Since Rh-negative blood is recessive, Rh-negative parents are homozygous for the recessive allele. Thus, two Rh-negative parents cannot
have an Rh-positive child.
Boy 6
no
Since Rh-negative blood is recessive, Rh-negative parents are homozygous for the recessive allele. Thus, two Rh-negative parents cannot
have an Rh-positive child.
Boy 7
yes
A child with AB blood is possible, if he gets an A allele from Mai and a
B allele from Paul. And Rh-negative blood is expected for all children
of Mai and Paul.
Boy 8
no
Child has type O blood, which means he cannot be Mai’s child since
Mai’s children must receive either an A or B allele.
©2006 The Regents of the University of California
Reason
Science and Life Issues Student Sheet 68.3 Key
D-191
Name
Date
Guide to the Lost Children
Fill in the table below with the possible allele combination(s) for each person. This will help you to
complete Student Sheet 68.2.
Type A
= AA or AO
(A is dominant over O)
Type B
= BB or BO
(B is dominant over O)
Type AB
= AB
(A and B are co-dominant)
Type O
= OO
(O is recessive)
Rh+
= Rh+Rh+ or Rh+Rh-
(Rh+ is dominant)
Rh-
= Rh-Rh-
(Rh- is recessive)
Table 1: Parents
Blood Type and
Possible Alleles
Rh Factor and
Possible Alleles
Rh+
Belinda
A
John
O
Mai
AB
Rh+
Rh-
Paul
B
Rh-
Table 2: Children
©2006 The Regents of the University of California
Blood Type and
Possible Alleles
Rh Factor and
Possible Alleles
Rh+
Girl 1
AB
Girl 2
A
Girl 3
O
Girl 4
B
Boy 5
AB
Boy 6
A
Boy 7
AB
Rh+
Rh-
Boy 8
O
Rh-
Science and Life Issues Student Sheet 68.1
RhRh+
RhRh+
D-193
Name
Date
Finding the Children of John and Belinda
Child
Could be John and
Belinda’s? (yes or no) Reasoning
Girl 1
Girl 2
Girl 3
Girl 4
Boy 5
©2006 The Regents of the University of California
Boy 6
Boy 7
Boy 8
Science and Life Issues Student Sheet 68.2
D-195
Name
Date
Finding the Children of Mai and Paul
Child
Could be Mai and
Paul’s? (yes or no)
Reason
Girl 1
Girl 2
Girl 3
Girl 4
Boy 5
©2006 The Regents of the University of California
Boy 6
Boy 7
.
Boy 8
Science and Life Issues Student Sheet 68.3
D-197