Transcript FORENSIC SEROLOGY Chapter 8

Chapter 8
FORENSIC SEROLOGY
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
8-1
Stain Patterns of Blood
• The location, distribution, and
appearance of bloodstains and spatters
give useful information for
reconstructing the events that produced
the blood.
• Surface texture and the stain’s shape,
size, and location must be considered
when determining the direction,
dropping distance, and angle of impact of
a bloodstain.
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
8-2
Stain Patterns of Blood
• Surface texture is important. The harder and less porous
the surface, the less spatter.
• The direction of travel of blood striking an object may be
determined because the pointed end of a bloodstain
always faces its direction of its travel.
• The impact angle of blood on a flat surface can be
determined by measuring the degree of circular
distortion. At right angles the blood drop is circular, as
the angle decreases, the stain becomes elongated.
• The origin of a blood spatter in a two-dimensional
projection can be established by drawing straight lines
through the long axis of several individual bloodstains.
The intersection or point of convergence of the lines
represents the origin point.
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
8-3
Projection of Blood
Forensic investigators can determine how
blood was projected from the body by
examining factors such as:
• Type of injuries
• The order in which the wounds were
received
• Whose blood is present
• The type of weapon that caused the
injuries
• Whether the victim was in motion or
lying still when the injury was inflicted
• Whether the victim was moved after
the injury was inflicted
• How far the blood drops fell before
hitting the surface where they were
found.
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
8-4
Blood & Crime Scene:
Categories of Blood Patterns
Pools of blood have evidentiary value in
collecting a wet sample. Drops of blood can
reveal the height and angle from which the
blood fell onto the surface. According to
forensic scientists, the blood spatter
analysis claims that blood which falls
perpendicular to the floor from a distance
of zero to two feet would create a circular
drop with slightly frayed edges. Drops from
a higher distance would have more distinct
tendrils extending off the edges.
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
8-5
Blood & Crime Scene:
Categories of Blood Patterns
A blood smear on the wall or floor can
indicate the direction of force of the
blow. The direction of force is always in
the direction towards the tail, or
smaller end, of the smear. In other
words, the largest area
of the smear is the point of origin. Blood
crusts must be tested with crystalline
techniques to verify that they are actually
blood. Refrigerated red blood cells have a
shelf life of about forty-two days, and the
serum containing white blood cells can be
refrigerated much longer, almost up to a
year. DNA can be extracted from blood (if
white blood cells which always contain a
nucleus are present), and also from sperm,
bone marrow, tooth pulp, and hair roots.
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
8-6
Blood & Crime Scene
Regardless of what type of analysis is used
on the blood at the crime scene, care must
be taken to handle it properly and to
prevent putrefaction. Photographs and
notes should be taken before any blood is
lifted. Samples should not be exposed to
heat, moisture, or bacterial contamination,
because these factors can shorten the
survival time of proteins, enzymes, and
antigens. Delays in bringing samples to the
lab must be avoided at all cost, because it
can diminish evidential value.
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
8-7
Court Significance
Experts in bloodstain examination are
usually law enforcement personnel. In
certain jurisdictions, a police investigator
or blood specialist may testify on the core
issue because blood evidence is usually a
vital aspect of the crime scene.
An expert in bloodstain examination has:
•Completed specialized training
•Conducted a sufficient number of
examinations
•Accumulated enough reference patterns
to reinforce an argument
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
8-8
Heredity and Paternity
• The transfer of hereditary material is
accomplished by means of units called genes,
located on chromosomes.
• Alleles: Alternative forms of genes that
influence a given characteristic (such as eye
color or blood type).
• Paternity testing has historically involved the
A-B-O blood typing system, along with blood
factors such as Rh (D).
• DNA test procedures raise the odds of
establishing paternity beyond 99%.
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
8-9
Principles of Heredity
•
Transmission of Traits
– Accomplished by genes, which is the basic unit of heredity.
– Genes are on chromosomes (46 in 23 pairs).
– The human egg and human sperm contain 23 chromosomes, which combine
•
during fertilization.
– A female has XX chromosome, and male has XY chromosome.
Transmission of Traits
– Genes and chromosomes come in pairs.
– The position of a gene on the chromosome is called the locus.
– Alleles are alternative forms of genes that influence an inherited
characteristic.
– An example of allele genes is the A-B-O blood type system.
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
8-10
Principles of Heredity
• Transmission of Traits
– A-B-O blood types:
• When a gene is made of two similar genes, they are said to
be homozygous. Examples include AA or BB.
• If the gene is made up of two different genes, it is said to be
heterozygous. An example would be AB.
• A and B genes are dominant, while O genes are recessive.
– A pair of A-B-O allele genes together are the genotype of an
individual.
– The phenotype of an individual is the outward characteristic of
the individual.
– There is no lab test to determine a person’s A-B-O genotype.
– If the genotypes of both parents are known, a Punnet square
may be constructed to determine potential genotype of
offspring.
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
8-11
Blood & DNA Testing
Blood is used in DNA testing, as shown by
the following steps:
1. Blood samples are collected from the
victim, defendant, and crime scene.
2. White blood cells are separated from red
blood cells.
3. DNA is extracted from the nuclei of
white blood cells.
4. A restrictive enzyme is used to cut
fragments of the DNA strand.
5. DNA fragments are put into a bed of gel
with electrodes at either end.
6. Electric current sorts DNA fragments by
length.
7. An absorbent blotter soaks up the
imprint; it
is radioactively treated, and an X-ray
photograph, called an autoradiograph, is
produced.
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
8-12
Forensic Characteristics of Semen
• Normal male can ejaculate 2.5-6 ml of
seminal fluid
• Each ml contains 100 million or more
spermatozoa
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
8-13
Testing for Semen
• Stain must be located and collected
• Acid Phosphatase Color Test
– Purple color indicates the presence of semen
• Spermatozoa Test
– Semen is diluted with water and dried on
filter paper
– Microscopic examination looks for
spermatozoa
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
8-14
Testing for Seminal Stains
• Many of the cases sent to a forensic laboratory involve
sexual offenses, making it necessary to examine exhibits
for the presence of seminal stains.
• The best way to locate and at the same time
characterize a seminal stain is to perform the acid
phosphatase (an enzyme found in seminal fluid) color
test.
– A purple color indicates acid phosphatase enzyme.
• Semen are identified by either the presence of
spermatozoa or of p30, a protein unique to seminal
plasma.
• Forensic scientists can link seminal material to an
individual by DNA typing.
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
8-15
Rape Evidence
• Presence of seminal fluid
• Physical injuries such as bruising or
bleeding confirms a violent sexual assault
took place
• Transfer of physical evidence—blood,
semen, fibers, and hair—are usually
present
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
8-16
Rape Evidence
• The rape victim must undergo a medical
examination as soon as possible after the
assault.
• At that time the appropriate items of physical
evidence including clothing, hairs, and swabs
can be collected for subsequent laboratory
examination.
• All outer and undergarments should be
carefully removed and packaged separately in
paper (not plastic) bags.
• Bedding, or any objects upon which the assault
took place, may also be carefully collected.
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
8-17
An antibody–antigen–antibody sandwich or complex is seen as a
colored band. This signifies the presence of PSA in the extract of a
stain and positively identifies human semen.
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
8-18
PSA testing by electrophoresis.
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
8-19
Collection of Rape Evidence
• All outer and undergarments are
collected and packaged separately in
paper bags
• Trace evidence is collected by standing
on a clean sheet while removing clothing
• Bedding may be recovered if seminal
stains are present
• Medical Examination of the victim
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
8-20
Rape Evidence
• If a suspect is apprehended within 24 hours of
the assault, it may be possible to detect the
victim’s DNA on the male’s underwear or on a
penile swab of the suspect.
• Items routinely collected from the suspect
include all clothing, pubic hair, head hair,
penile swab, and a blood sample or buccal swab
for DNA typing.
• The forceful physical contact between victim
and assailant may result in a transfer of such
physical evidence of blood, semen, saliva, hairs,
and fibers.
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
8-21
Medical Examination of Victim
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Pubic Combings
Pubic Reference Samples from victim
Vaginal swabs and smear
Rectal swabs
Oral swabs
Head hairs
Blood sample
Fingernail scrapings
All clothing
Urine specimen
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
8-22
Medical Examination of Suspect
• All clothing
• Pubic hair combings
• Pulled head and pubic hairs for reference
samples
• Penile swab
• Blood sample or buccal swab
FORENSIC SCIENCE
An Introduction
By Richard Saferstein
PRENTICE HALL
©2008 Pearson Education, Inc.
Upper Saddle River, NJ 07458
8-23