FORENSIC SEROLOGY

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FORENSIC SEROLOGY

• Chapter 8, Part 2

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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 stains shape, size, and
  location must be considered when determining the
  direction, dropping distance, and angle of impact
  of a bloodstain.

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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.

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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.

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Blood Crime SceneCategories 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.

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Blood Crime SceneCategories 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.

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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.

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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

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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.

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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.

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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 persons
  A-B-O genotype.
• If the genotypes of both parents are known, a
  Punnet square may be constructed to determine
  potential genotype of offspring.

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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.

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Forensic Characteristics of Semen

• Normal male can ejaculate 2.5-6 ml of seminal
  fluid
• Each ml contains 100 million or more spermatozoa

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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

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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.

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Rape Evidence

• Presence of seminal fluid
• Physical injuries such as bruising or bleeding
  confirms a violent sexual assault took place
• Transfer of physical evidenceblood, semen,
  fibers, and hairare usually present

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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.

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An antibodyantigenantibody 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.
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PSA testing by electrophoresis.
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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

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Rape Evidence

• If a suspect is apprehended within 24 hours of
  the assault, it may be possible to detect the
  victims DNA on the males 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.

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Medical Examination of Victim

• 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

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Medical Examination of Suspect

• All clothing
• Pubic hair combings
• Pulled head and pubic hairs for reference samples
• Penile swab
• Blood sample or buccal swab