Snowball the Cat and Other
Tales of Forensic Science
Donna C. Sullivan, PhD
Division of Infectious Diseases
University of Mississippi Medical
Center
Polymorphism



A DNA polymorphism is a sequence
difference compared to a reference
standard that is present in at least 1–2%
of a population.
Polymorphisms can be single bases or
thousands of bases.
Polymorphisms may or may not have
phenotypic effects.
Types of Polymorphic DNA
Sequences




RFLP: restriction fragment length
polymorphisms
VNTR: variable number tandem repeats (8
to >50 base pairs)
STR: short tandem repeats (1–8 base
pairs)
SNP: single-nucleotide polymorphisms
DNA DIFFERS PERSON TO
PERSON


All individuals genetically unique (except
identical twins)
Differences in DNA sequence detected by



RFLP using large quantities intact DNA
PCR in conjunction with various methods
Single nucleotide polymorphisms (SNPs)
DNA Profiles from12 Unrelated
Individuals At ONE Polymorphic Locus
RFLP ANALYSIS: Detect Alleles by
Southern Blot Hybridization



Analysis of VNTR locus by Southern blot
most commonly results in two-band
pattern, comprised of a band inherited
from each parent
Single band patterns possible with 2
alleles of same size
For 3 different alleles, six different
genotypes possible
RFLP Analysis: Detect Alleles
by Southern Hybridization
Restriction Fragment Length
Polymorphisms


RFLP genotypes are inherited.
For each locus, one allele is inherited from each
parent.
Father
Locus
1
2
Mother
Locus
1
2
Parents
Southern blot
band patterns
Locus
1
2
Child
CALCULATION OF POSSIBLE
GENOTYPES




For N different alleles, total possible
genotypes:
(n X (n+1))
2
For 3 alleles, 6 genotypes
For 4 alleles, 10 genotypes
For 5 alleles, 15 genotypes
VNTR: Variable Number
Tandem Repeats




Short sequence of DNA repeated in headto-tail fashion
Occur at specific chromosomal locations
Interspersed throughout human genome
Number of repeated units vary between
individuals
Multiple Alleles at VNTR loci
Distinguish Individuals by
Combination of Alleles at VNTR
Loci
Short Tandem Repeat
Polymorphisms (STR)

STR are repeats of nucleotide sequences.






AAAAAA… - mononucleotide
ATATAT… - dinucleotide
TAGTAGTAG… - trinucleotide
TAGTTAGTTAGT… - tetranucleotide
TAGGCTAGGCTAGGC… - penta nucleotide
Different alleles contain different numbers of
repeats.


TTCTTCTTCTTC - four repeat allele
TTCTTCTTCTTCTTC - five repeat allele
Short Tandem Repeat
Polymorphisms

Allelic ladders are standards representing
all alleles observed in a population.
11 repeats
(Allelic ladder)
5 repeats
Genotype: 7,9
Genotype: 6,8
Evidence Testing by STR-PCR
Which suspect—S1 or S2—was at the crime scene?
(V = victim, E = crime scene evidence, M = molecular
weight standard)

M S1 S2 V E M
Locus 1
M S1 S2 V E M
Locus 2
M S1 S2 V E M
Locus 3
Short Tandem Repeat Polymorphisms
by Multiplex PCR
FGA
PentaE
TPOX
D18S51
D2S11
D8S1179
THO1
vWA
D3S1358
STR-PCR

STR genotypes are inherited.
Child’s alleles
Mother’s alleles
Father’s alleles

One allele is inherited from each parent.
Single Nucleotide Polymorphisms
(SNP)
Single-nucleotide differences between DNA
sequences.
 One SNP occurs approximately every 1,250
base pairs in human DNA.
 SNPs are detected by sequencing, melt
curve analysis, or other methods.
 99% have no biological effect;
60,000 are within genes.

Top Ten Ways to Know that You
are a Forensic DNA Scientist
10.You have your children’s DNA profiles framed on your
desk instead of their pictures.
9.When your children hurt themselves, you are more
interested in collecting their blood to generate a DNA
profile than getting them cleaned up…
8.Your pockets are full of napkins with DNA sequences
written on them.
7.You want to name your first four kids: Adenine, Thymine,
Guanine, and Cytosine.
6.You wonder how jello would work as a separation
medium…and have tried it when no one else was
around…but were too afraid to publish the results.
Top Ten Ways to Know that You
are a Forensic DNA Scientist
5.You want to start a paternity testing
business for all those who appear on the
Jerry Springer show.
4.You know that DNA stands for more than
the National Dyslexics Association.
3.You want to do a study on the genetics of
inbreeding…and have selected the
Reservoir deer population for a case
study.
Top Ten Ways to Know that You
are a Forensic DNA Scientist
2.You know that “scientists” on the popular
TV show CSI: Crime Scene Investigation
cannot possibly get their DNA results
within the timeframe of a single
commercial break.
1.Your license plate reads: OJ DID IT!
LOCARD TRANSFER THEORY
“When two objects come in
contact,
traces from one will be
transferred from one to another,
and in both directions.”
FORENSCI SCIENCE CONCEPTS

Identification



Classification: characteristics shared by items
(Firearms, Shoes)
Groups (Same type of gun, same size shoe)
Individualization



Created by random acts (rifling on bullets)
Fingerprints (influenced by environmental,
developmental factors)
Traits that are so rare, alone or in combination, that
they can not be duplicated by chance
DNA Identification Applications







Sexual assault
Homicide and other violent crimes
Exculpate wrongly accused suspects
Identify serial crimes
Identify human remains
Sex offender tracking
Parentage testing
In The Beginning




Alec Jeffreys, geneticist at University of
Leicester, UK
Coined the term “DNA fingerprinting”
RFLP analysis
Demonstrated that forensic samples, even
dried stains several years old, contained
sufficient DNA to yield conclusive results
Finding A Pitchfork In The Haystack:
Midlands Rapes
Two British schoolgirls raped and
murdered
 Kitchen porter at an insane asylum
confessed to one of the murders
 Were both crimes committed by the
same man?
 Did the kitchen porter do it?

Finding A Pitchfork In The Haystack:
Midlands Rapes

Semen samples from rape/murder scenes:


Blood sample from kitchen porter:


Both crimes committed by same man
Did not match crime scene evidence
Police felt that the murderer was a local


Tested DNA from every man between the age
of 17-34 (4,582 men) in the local area
No matches found
Finding A Pitchfork In The Haystack:
Midlands Rapes

Local baker over-heard some colleagues in
a pub


Colin Pitchfork, another baker, had convinced
another employee to give blood in his place
Police arrested Pitchfork (he immediately
confessed)

Pitchfork’s DNA was perfect match to crime
scene evidence (4,583rd man tested)
Evaluation Of Evidence

Establish type of biological material
present in sample



Is it blood? Catsup?
Is it human blood?
“State of the DNA”



How much degradation of the DNA is there?
How much total DNA is present?
How much DNA is human?
Forensic Blood Typing
 ABO
groups
 Phosphoglucomutase (PGM)
 Erythrocyte acid phosphatase
(EAP)
 Haptoglobin
 Adenylate kinase (AK)
Semen Can Be Identified With
Several Laboratory Tests

Acid Phosphatase - a presumptive test

Anti P30 - a quantitative and qualitative
test that identifies the presence of the
protein P30 found only in human semen

Spermatozoa search - a microscopic
analysis visually observing the presence of
sperm cells
HLA DQ/HLA DQA1 System




HLA: human lymphocyte antigens
Determine whether patient has antibodies
against a potential donor’s HLA antigens
HLA DQ  is historic name for this region
A 242 bp region with variation detected
with specific probes for subregions
HLA DQ/HLA DQA1 System



Original test could detect 6 common DQ 
alleles, 21 possible genotypes
Subsequent analysis, renaming by
geneticists resulted in DQA1 test,
increased number of subtypes detected
(up to 28 detectable types)
Cheap, fast color reactions
Mixed Vs Contaminated
Samples

MIXED SAMPLES



Contain DNA from more than one individual
Mixing occurs before or during commission of
a crime
CONTAMINATED SAMPLES

Materials deposited during collection,
preservation, handling or analysis
HOW MUCH SAMPLE DO YOU
NEED?
Gender Identification

Amelogenin gene for tooth pulp found on sex
chromosomes ( one on X, one on Y)

Different size PCR products from X and Y copies of
the gene:



X Chromosome 106 bp PCR product
Y Chromosome 112 bp PCR product
“Right side primers”

Located to right of amelogenin gene, included
amelogenin gene


X chromosome 549 bp (set 1), 977 bp (set 2)
Y Chromosome 360 bp (set1), 788 bp (set2)
DNA/CSI Quiz
True or false:
 DNA results take 8 minutes
 DNA results can tell
investigators what a
suspect looks like
 All CSIs are good looking
and solve crimes wearing
Armani
 CSI investigators drive
Hummers, especially in
Florida

Compliments of Linda Ledray
The Combined DNA Index
System (CoDIS)



A database of DNA profiles from violent
felons and crime scene samples
Laws concerning who is eligible for the
database vary from state to state
Database currently contains about
2,038,470 felons and 93,956 crime scene
profiles (19,00 hits so far)
The Mystical Power of CoDIS


Extremely powerful
investigative tool, linking
crimes, and pulling suspects
out of thin air!
Can prevent, as well as solve
crimes!

NOT!!!!
Different Systems, Different
Markers
CODIS Profile
STR Data (cont’d)
STR data (cont’d)
STR TYPING SUMMARY SHEET
Date:
DNA Analyst / Serial #:
9/24/1999
MATTHIES
Item #
25(S)
25(E)
VICTIM
SUSPECT
AMEL
D3S1358
X, Y
17
X, Y
17
X
15, 17
X
15, 17
X
15, 17
X
15, 17
X, Y
17
X, Y
17
vWA
FGA
DR #:
V9780
D8S1179
15, 17 23, 26 14, 15
00-00-00001
D21S11
D18S51
D5S818
D13S317
26
12, 15
10
9, 13
D7S820
8, 10
D16S539
THO1
TPOX
9, 10
8, 9
9, 10
11, 12
7, 8
11
11, 12
7, 8
11
9, 10
8, 9
9, 10
8, 10
16, 18 19, 26
16, 18 19, 26
15
15
15, 17 23, 26 14, 15
28,
32.2
14, 16
28,
32.2
14, 16
26
12, 15
8, 13
12
11
11
8, 13
12
11
11
10
9, 13
8, 10
8, 10
“The DNA profile obtained from Item 25(S) matches the
DNA profile of the suspect. The combination of genetic
marker types exhibited by Item 25(S) and the suspect
occurs in approximately one in one hundred quadrillion
(1017) individuals…”
POPULATION DATABASES:
STR Analysis


Probability calculations based on knowing
allele frequencies for a representative
population
For a heterozygous individual, if the two
alleles have frequencies of p and q in a
population, probability (P) of having both
alleles at a single locus
P=2pq
Mitochondrial DNA (mtDNA)
Mitochondrial DNA
Polymorphisms
Mitochondria are maternally inherited.
 There are an average of 8.5 base
differences in the mitochondrial HV
sequences of unrelated individuals.
 All maternal relatives will have the same
mitochondrial sequences.
 Mitochondrial typing can be used for legal
exclusion of individuals or confirmation of
maternal lineage.

Y-STRs


Problem:
~99% of violent crimes are committed
by men
DNA Mixtures of male suspect and
female victim can pose an analytical
challenge, especially when the female
contribution is much greater than the
male = preferential amplification
Y-STRs

Solution:
Test for markers found only on the Ychromosome. Only male DNA is
amplified!
Y-STRs


Lower power of discrimination - paternal
relatives all share the same Y-STR
haplotype (“Wicked Uncle Ernie” Defense)
10% of Central Asian males share the
same Y-STR haplotype, thought to belong
to Genghis Khan
Serial Killer Case


Sept. 15, 1990, Prague: woman found
strangled, apparently sexually assaulted
Jan. 1991-April 1992, Austria: bodies of
7 prostitutes discovered in wooded
areas in different parts of Austria



Missing between 16-353 days
Same cause of death, pattern of disposal and
positional posing of bodies
No relevant biological evidence suitable for DNA
analysis
Serial Killer Case

May, 1991, Austria: potential suspect
identified by retired homicide detective


Similar to 1975 case in Germany in which
18 year old girl strangled with her own
brassier
June-July, 1991, Los Angeles: bodies of
3 prostitutes discovered


Strangled with their own brassieres
Linked all three based on characteristics of
cuts to bras, knots used
Serial Killer Case



Suspect arrested in German case in 1975,
convicted, sentenced to life in prison
(which means he got out on parole in
May, 1990)
While in prison, man became an author
and journalist
Police able to tract suspect’s movements,
match with times of murders in Prague,
Austria, Los Angeles
Serial Killer Case

Circumstantial evidence:




Travel activity
No alibi
Similarity to Prague murder for which he had been
convicted
Physical evidence (June, 1992)

Several head hairs found on the seat of suspect’s
BMW (driven in Sept. 1990, sold, scraped--except the
seats, which remained in a garage for 18 months)
Hair Found On Suspect’s Car
Seat
Serial Killer Case



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
Isolated 9 nanograms human DNA from
hair
June, 1993: 2 ng for HLA-DQA typing
(1:13 match to Prague victim)
Amplitype PM PCR typing: confirmation of
match and frequency of 1 in 2,300
April, 1994: 2 ng for STR analysis (3 loci)
June, 1994: 1 ng for Amelogenin locus
Serial Killer Case
VICTIM EVIDENCE
Serial Killer Case


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Discrimination to 1 in 2.1 million women
Confirmed identity of individual contributing the
hair sample recovered from car seat by reverse
paternity
Suspect convicted in Austrian court system,
sentenced to life in prison for murder of nine
women, including the Prague murder
Suspect committed suicide by hanging himself in
jail
Child Molestation Case
Example of Actual DNA
Evidence Presented to a Jury
DNA Profile Warrant
How Do You Identify Someone
Who Has Never Been Genotyped?



Need genetic information from their family
members
Parents: Half of the missing persons
alleles must be present in one parent, half
in the other parent
Spouses and children: Half of the genes
from child will be from spouse, half from
missing parent
MISSING FATHER: What is his
genotype?
1. Child (A, C)
2. Child (C, D)
3. Mother (B, C)
4. Child (B, D)
5. Child (A, B)
Missing Father must
be A and D genotype.
MISSING MOTHER: What is
her genotype?
1.
2.
3.
4.
5.
Father (B and C)
Child (A, B)
Child (A, C)
Child (B, D)
Child (C, D)
Missing Mother must
be phenotype A and D
Using Personal Effects to Identify
Remains
Using Family Members to Identify
Remains
PRENATAL DIAGNOSIS OF
RAPE VICTIMS



Study looked at 10 victims of sexual
assault who became pregnant
Prior to testing they were interviewed
about continuing the pregnancy
All women had a consensual partner who
was also potential father of unborn child
PRENATAL DIAGNOSIS OF
RAPE VICTIMS


Inclusion: match between husband and
fetus
Exclusion: no match between husband
and fetus
(Rule out, rule in. In criminal cases, may
obtain inconclusive result)
PRENATAL DIAGNOSIS OF
RAPE VICTIMS
CASE RESULTS: In Utero
Paternity Testing
Case
Marital
status
Police
Report
Pre Test
Attitude
Partner
Paternity
Probability
1
Married
No
Termination
99.99
Continue
2
Married
No
Termination
99.95
Continue
3
Married
No
Termination
0.00
Terminate
4
Engaged
Yes
Adoption
99.99
Continue
5
Single
No
Adoption
99.99
Continue
6
Married
No
Termination
0.00
Terminate
7
Married
No
Adoption
99.99
Continue
8
Single
No
Adoption
0.00
Continue
9
Married
No
Termination
99.19
Continue
10
Married
No
Termination
0.00
Terminate
Hammond et al, JAMA 273: 1774 (1995)
Pregnancy
Decision
Snowball the Cat: Prince Edward
Island, Canada




In 1994, Shirley Duguay, a 32-year-old mother of five,
disappeared. Her body was found in a shallow grave a
few months later.
Among the chief suspects in the murder was the
woman’s estranged common-law husband, Douglas
Beamish, who was living nearby in his parents’ home.
Royal Canadian Mounted Police had no evidence linking
Beamish to the crime.
During the search for the victim’s body, however, the
Mounties discovered a plastic bag containing a leather
jacket with blood stains that matched the victim’s blood.
Snowball the Cat: Prince Edward
Island, Canada



The jacket also contained 27 strands of
white hair, which forensic investigators
determined were from a cat.
The Mounties remembered a white cat
named Snowball living in Beamish’s
parents’ home.
The trick was to prove the cat hair found
in the jacket was Snowball’s.
“Meow Plex”: Cat STR
Angiosperm Witness for the
Prosecution



A young woman was murdered in Phoenix,
Arizona, and a pager found at the scene of the
crime led the police to a prime suspect.
He admitted picking up the victim, but claimed
she had robbed him of his wallet and pager.
The forensic squad examined the suspect's
pickup truck and collected pods later identified
as the fruits of the Palo Verde tree (Cercidium
spp.).
Angiosperm Witness for the
Prosecution



One detective went back to the murder scene and found
several Palo Verde trees, one of which showed damage
that could have been caused by a vehicle.
The detective's superior officer innocently suggested the
possibility of linking the fruits and the tree by using DNA
comparison.
A geneticist at the University of Arizona in Tucson
agreed to take on the case.


Established evidence that individual Palo Verde trees have
unique patterns of DNA.
It was then a simple matter to link the pods from the
suspect's truck to the damaged tree at the murder scene
and obtain a conviction.
Viral DNA/RNA Evidence Convicts
Doctor



Dr. Richard Schmidt had an extramarital
affair with his nurse, Janice Trahan.
The relationship terminated when the
doctor refused to leave his wife.
The doctor and nurse continued their
working relationship, with the nurse
allowing the doctor to continue to
administer a series of Vitamin B-12 shots.
Viral DNA/RNA Evidence Convicts
Doctor




The nurse’s health began to deteriorate shortly
after one treatment and she received notification
that she had contracted HIV and hepatitis.
Analysis of HIV strain from nurse closely
resembled that of a strain from one of the
doctor’s patients.
The doctor was charged and convicted to
attempted second degree murder.
He was sentenced to 50 years of hard labor.
The Remains Of The Evangelist
Luke




Luke was born in Antioch, Roman province
of Syria
Died in Thebes, Greece, at age of 84,
around 150 AD
Buried in Thebes but moved to
Constantinople around 338 AD
Body moved to Padua, Italy, sometime
before 1177 AD
The Wandering Saint
Analysis Of The Remains



Removed two teeth and extracted DNA
Isolated control region of mitochondrial
DNA and cloned it
Compared sequences from body to
sequences of DNA from



Ancient and modern Greeks
Ancient and modern Turks
Ancient and modern Syrians
Teeth Removed From The Religious Relic:
The body of St. Luke?
Is This St. Luke?
The body is right age
 The body is not Greek
 Highest probability is that the body
belonged to a Syrian but it is very
difficult to tell Syrians from Turks
