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CASE STUDIESFORENSIC PROFILING Case Study 1Who Killed
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CASE STUDIES?FORENSIC PROFILING
Case Study 1?Who Killed Maggie Mortis?
September 15 2008: Maggie Mortis, a forensic scientist in the Gotham City Crime
Lab was found dead in her lab. She was working last night on DNA from a homicide
investigation. No equipment was stolen from the lab, but DNA samples were missing. Two
suspects are in custody?both were seen earlier talking to Ms. Mortis at the corner
DNA samples were collected from each suspect, the
1 2 3 4 5 6 7 8 9 10
lab director, and the victim Ms. Mortis. DNA was isolated
from several crime scene samples including skin cells
found under the fingernails of the victim, a few discarded
sunflower seed shells, a wad of chewing gum, and a
urine sample found on one of the walls of the lab.
DNA samples collected in this case were prepared
by PCR. Three loci (D16S539, D7S820, and D13S317)
were loaded and separated on an acrylamide gel. Results
are shown on the right. There are 10 lanes identified
D16S539 locus ?
across the top of the gel picture. Each lane contains the
DNA profile of a different individual or crime scene
sample. Lanes 1?4 show the DNA profile of people
associated with the crime. The fifth lane shows an allelic
marker. This is a commercially prepared sample that
carries the common alleles for each locus. The name of
each allele is marked on the right hand side of the gel.
The markers allow you to identify and name the alleles
carried by an individual. As an example we can see that
D7S820 locus ?
Suspect 1 (lane 2) has alleles 11 and 10 at the D7S820
locus. The four crime scene samples are shown in lanes
6?9. Lane 10 carries a second allelic marker.
Start by identifying the alleles carried by each
individual in the chart below. Then try to match them
with one or more of the crime scene samples. The alleles
for the first sample have been filled to show you how it is
1. Who is the most likely suspect to murder
Maggie Mortis? Explain your reasoning.
7 D13S317 locus ?
1. Maggie Mortis
2. Suspect 1
3. Suspect 2
4. Lab Director
5. Allelic marker
6. Gum sample
7. Seed sample
8. Urine sample
9. Fingernail sample
10. Allelic Marker Sample ID
Fingernail sample D16S539 D7S820 D13S317 9,9 10,10 8,14 Case Study 2: Whose Baby is it anyway?
A sudden shift in direction, and increase in the intensity of Hurricane Phillip
prompted an immediate unscheduled evacuation of the small coastal town of Longhorn,
Texas. This included an emergency evacuation of the local hospital. At the time of
evacuation three newborn infants were being cared for in the pediatric ward. In the rush
and chaos of the evacuation, the ankle identifiers of the infants were somehow removed
(possibly as a result of foul play?). All three babies and their parents were safely evacuated
to another hospital, but the question of which baby belongs to which parent now surfaces.
DNA profiles were prepared for each infant and each parent. Your job as analyst will be to
match each of the scrambled infants with the proper set of parents.
In this case study, a fingerprint of 3 loci
1 2 3 4 5 6 7 8 9 10 11
(D16S539, D7S820, and D13S317) was used to
match parents and infants. There are 11 lanes
identified across the top of the gel picture. Each
lane contains the fingerprint of a different
individual. Lanes 1?3 show the DNA profile of the
scrambled infants. Each infant was labeled with a
number. The fourth lane shows an allelic marker.
This is a commercially prepared sample that carries
the common alleles for each locus. The name of
D16S539 locus ?
each allele is marked on the right hand side of the
gel. The markers allow you to identify and name
the alleles carried by an individual. As an example
we can see that infant 3 has alleles 11 and 9 at the
D7S820 locus. The three sets of parents are shown
in lanes 5?10. Each parent is labeled with letters.
Lane 11 carries a second allelic marker.
You can start unscrambling the infants by
identifying and writing down the genotypes for each
set of parents at the D7S820 locus. Then, recalling
D7S820 locus ?
that the infant must have one allele from each
parent, write down the possible infant genotypes.
There can be as many as 4 possibilities but in some
cases there will be less. For example if the parents
share the same allele then there are really only
three possibilities. If one of the parents is
homozygous, meaning that both copies are the
same allele, then there are only two possibilities. A
worksheet on the following page has been prepared
to help you. Next, write down the infant genotypes
and see if any of them are only found in the
D13S317 locus ?
possibilities of one set of parents. If this is the
case, confirm your hypothesis by looking at the
1. Infant 1
remaining two loci for that match and make sure
that the parents match the infant. To fully separate
2. Infant 2
all the infants to their rightful parents you will
3. Infant 3
probably have to repeat the analysis with one or
4. Allelic marker
both additional loci.
5. Father A 6. Mother A
7. Mother B
8. Father B
9. Mother C
10. Father C.
11. Allelic Marker 2. Which infant belongs to which set of
parents? Support your conclusion with genetic
evidence and reasoning. Parent Analysis Worksheet
Use the following tables to help you analyze the scrambled baby case study. First
identify the two alleles for Father A. Write one allele in box 1 and the other in box 2. Next
identify the two alleles for Mother A and write one in box 3 and the other in box 4. The
white boxes (5?8) are used to determine the possible allele outcomes in the baby. Fill in box
5 with the allele from box 1 and box 3. Fill box 6 with the alleles from box 2 and box 3.
Continue the pattern for boxes 7 and 8. Repeat this procedure for Parents B and C in the
additional tables. (Some of you may recognize these boxes from previous classes as a
Punnett square.) Next, determine the genotype for each infant and place it in the fourth
table (boxes 9?11). Finally, compare the infant?s genotype with the possible genotypes from
each parent (boxes 5?8). If a match occurs write that parent?s letter id in the boxes labeled
?Parent matches? (boxes 12?14). The infant genotype may match more than one parent
group so make sure you compare all three parent groups. When finished if an infant
matches to only one parent group then you can hypothesize that the infant belongs to those
parents. Be sure to check your hypothesis using the other two loci. Although the tables are
not pre-drawn for you a similar analysis can be performed for the D13 and D16 loci. Father A
1 2 3 5 6 4 7 8 Locus
D7S820 Father C Mother C Infant
1 Notes and Observations: Father B Mother B Mother A Locus
3 Genotype Parent
es 9 12 10 13 11 14 Case Study 3: Identity of the Unknown Soldier
Lt. Jason Painter was reported missing in action during the Vietnam War, leaving a
wife and two small children back at home. Although he was assumed dead, no remains were
ever found and the family has been forced to live with the burden of uncertainty as to the
whereabouts and condition of their husband and father. Recently, humanitarian expeditions
into Vietnam have uncovered a mass grave site containing the remains of several US
soldiers. Three of the six soldiers were identified by personal artifacts found on their bodies
as members of Lt. Painter?s platoon. The remaining three
1 2 3 4 5 6 7 8 9
bodies appear Caucasian but carried no means of
identification. DNA samples were collected from each
Unknown Soldier. Since he was reported missing long
before DNA technology permitted profiling, there is not a
reference sample of Lt. Painter to confirm identity.
However, the Painter family was contacted and submitted
samples for testing from Sally Painter (the wife), Jessica
D16S539 locus ?
Painter (the daughter), and John Painter (Jason?s Father).
Profiles for the three unknown soldiers and the three
Painter family members are provided. As an analyst, you
will try to recreate, if possible, Jason painter DNA profile
and see if it matches any of the three unknown soldiers.
By now, you should be used to reading gels. Use the
three known DNA profiles to provide clues to the profile for
6 D7S820 locus ?
8 D13S317 locus ? 7 1. Allelic marker
2. Unknown Soldier 1
3. Unknown Soldier 2
4. Unknown Soldier 3
5. Allelic marker
6. John Painter (father)
7. Jessica Painter (daughter)
8. Sally Painter (wife)
9. Allelic Marker 3. Is it possible that any of the tested unknown
soldiers might be Lt. Painter? If so, which one?
Explain how you arrived at this conclusion using the
provided genetic information. Calculating Locus and Profile Frequencies.
Allele frequencies in Caucasian (US) population for 3 STR Loci
Allele D16S539 D7S820 D13S317
Frequency Calculations Review
----Allele frequencies: the distribution of an allele in the
general population. These are measured in the general
population by the National Institute of Standards and
Technology. Allele frequencies are different for different
populations. Allele frequencies are represented by the
letters p and q. (It doesn?t matter which is which but it
is common to label the frequency for the smaller allele p
and the frequency for the larger allele q)
Locus Frequencies: The probability that two alleles will
occur in a single genotype. The Locus Frequency is
calculated using the equation 2pq if the alleles are
different or p2 if the alleles are the same.
Profile Frequencies: Also called the Random Match
Probability (RMP). The probability that two multi-loci
profiles will match due to chance. It is calculated by
multiplying the Locus frequency for each locus
used in the profile.
Use the allele frequencies provided in the table above to calculate the locus frequency and
the profile frequency for the following individuals.
4. Locus frequency of D7S820 for Maggie Mortis 5. Profile frequency for suspect 2 6. Locus frequency of D16S539 for Infant 1 7. Profile frequency for Father B 8. Locus frequency of D13S317 for Sally Painter 9. Profile frequency for Unknown Soldier 3
This question was answered on: Feb 21, 2020
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