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Biological Fluids: Blood, Semen, Saliva, and an Introduction to DNA

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Title: Biological Fluids: Blood, Semen, Saliva, and an Introduction to DNA


1
Chapter 13
  • Biological Fluids Blood, Semen, Saliva, and an
    Introduction to DNA

2
Objectives
  • Students should gain an understanding of
  • Tests for the presence of blood
  • Serological blood typing
  • Tests for the presence of saliva
  • Tests for the presence of semen
  • The principles of paternity
  • DNA, genes, and chromosomes
  • Mitochondrial DNA

3
Introduction
  • Prior to the development of DNA typing, forensic
    serology was the primary technique of crime labs.
  • Most labs still use basic serological testing
    procedures.
  • Some do not have a DNA typing facility owing to
    either a lack of resources or a lack of enough
    cases to warrant the investment.

4
Blood (1 of 2)
  • Plasma the liquid portion of blood
  • Accounts for 55 of the total blood volume
  • Consists of 90 water and 10 dissolved materials

5
Blood (2 of 2)
  • Cellular components of blood
  • Account for 45 of the total blood volume
  • Include three major types
  • Erythrocytes red blood cells
  • Leucocytes white blood cells
  • Thrombocytes platelets

6
Tests for the Presence of Blood (1 of 6)
  • Police want to answer three questions
  • Is this blood?
  • Is it from a human?
  • How closely does it match the blood of the victim
    or the suspect?

7
Tests for the Presence of Blood (2 of 6)
  • Presumptive tests for blood
  • Luminol sprayed directly on bloodstained object
    produces a glow when it contacts blood
  • Color tests

8
Tests for the Presence of Blood (3 of 6)
  • Serological tests for blood precipitin
    serological test
  • Determines if blood is of human origin
  • Can be used with antiserum prepared for other
    animals if it is negative for human blood
  • Requires only a small blood sample
  • May produce a positive result even if bloodstains
    were washed down to a tiny sample remaining
  • Is highly sensitive even when bloodstains are odd

9
Tests for the Presence of Blood (4 of 6)
  • Serological blood typing
  • ABO system separates human blood into four broad
    classifications based on the presence or absence
    of the antigen A or antigen B on the surface of
    red blood cells
  • Rh factor expressed as positive or negative

10
Tests for the Presence of Blood (5 of 6)
  • Because blood types are inherited from a persons
    parents, blood types may become concentrated
    among certain ethnic groups.
  • 80 of the population are secretorsthey have
    significant concentrations of antigens in other
    body fluids.

11
Tests for the Presence of Blood (6 of 6)
  • Other blood typing systems based on the presence
    of proteins in red blood cells
  • Polymorphic proteins occur in multiple forms.
  • Different forms can be identified and their
    statistical occurrence in the population
    calculated.
  • The more independent factors that can be
    identified in a blood sample, the smaller the
    percentage of the population possessing that
    combination of blood traits.

12
Forensic Characterization of Saliva (1 of 2)
  • Characteristics of saliva
  • Consists of more than 99 water
  • pH range 6.87.0
  • Contains salivary amylase (a digestive enzyme)
  • Produced in three main pairs of salivary glands
    parotid, submaxillary, sublingual
  • Cleanses mouth and provides lubrication

13
Forensic Characterization of Saliva (2 of 2)
  • Saliva is always present at the crime scene if
    there are bit marks on the victim.
  • It can be used to identify an individual through
    DNA profiling.

14
Forensic Characterization of Semen (1 of 2)
  • Characteristics of semen
  • Consists of more than 90 water
  • pH range 7.27.4
  • A crime scene may include a large number of items
    stained by semen (e.g., garments, bed clothing,
    rugs, drapes, solid surfaces).

15
Forensic Characterization of Semen (2 of 2)
  • Identification of semen
  • At the crime scene UV light
  • Presumptive tests acid phosphatase test, p30
    test
  • In the laboratory direct observation of sperm
    under a microscope

16
Rape Evidence Collection (1 of 4)
  • Conviction often hinges on the ability to link
    the perpetrator to the victim and the victims
    injuries.
  • Gather evidence from both the physical
    surroundings and the victim
  • Collect the victims clothing if the victim is
    still at the scene
  • Ensure that the victim is examined by a physician
    immediately

17
Rape Evidence Collection (2 of 4)
  • Physical evidence collected from the victim
  • Blood sample Head hair
  • Combings from pubic hair Fingernail scrapings
  • Pubic hair reference samples Oral swab
  • Vaginal swab and smear All clothing
  • Rectal swab and smear Urine specimen

18
Rape Evidence Collection (3 of 4)
  • Saliva residues
  • Collect saliva from the victims skin if the
    assailant bit, sucked, or licked an area of the
    victims body

19
Rape Evidence Collection (4 of 4)
  • Physical evidence collected from the suspect
  • All clothing
  • Combings of pubic hair
  • Head hair and pubic hair standards
  • Penile swab
  • Blood sample

20
Principles of Paternity (1 of 4)
  • Nucleus largest structure in a human cell
    controls heredity
  • Ribosomes site of protein synthesis
  • Mitochrondria site of energy production

21
Principles of Paternity (2 of 4)
  • Chromosomes hereditary material found in the
    nucleus
  • Egg cell contains an X chromosome
  • Sperm contains either an X or a Y chromosome
    determines the sex of the offspring

22
Principles of Paternity (3 of 4)
  • Chromosomes are made of nucleic acids.
  • Deoxyribonucleic acid (DNA) is the primary
    hereditary material.
  • DNA consists of a series of coding regions and
    noncoding regions that are arranged along the
    chromosomes.
  • Genes are sections of the DNA molecule.
  • Pairs of chromosomes are considered homologous
    because they are the same size and contain the
    same information.

23
Principles of Paternity (4 of 4)
  • When fertilization occurs, one chromosome is
    inherited from the mother and one is inherited
    from the father.
  • Sons inherit their Y chromosome from their
    father, so paternity can often be determined by
    comparison of the Y chromosomes from father and
    son.

24
Introduction to DNA (1 of 13)
  • Functions of nucleic acids
  • DNA and RNA are responsible for storage and
    transmission of genetic information.
  • They determine how genetic information is
    transferred from one cell to another and how
    genetic traits are transferred from parents to
    offspring.
  • The major function of DNA is control and
    direction or protein synthesis in body cells.

25
Introduction to DNA (2 of 13)
  • Nucleic acids are composed of long chains of
    repeating units (nucleotides).
  • Each unit includes three components
  • Sugar
  • Nitrogen-containing heterocyclic base
  • Phosphoric acid unit

26
Introduction to DNA (3 of 13)
  • A nucleic acid can contain any of five bases
  • Adenine double-ring base (a purine)
  • Guanine double-ring base (a purine)
  • Cytosine single-ring base (a pyrimidine)
  • Thymine single-ring base (a pyrimidine)
  • Uracil single-ring base (a pyrimidine)

27
Introduction to DNA (4 of 13)
  • Structure of nucleic acids
  • Adenine, guanine, and cytosine found in both DNA
    and RNA
  • Thymine found in DNA
  • Uracil found in RNA

28
Introduction to DNA (5 of 13)
  • Primary structure of a nucleic acid sequence of
    the four bases
  • Secondary structure the double helix

29
Introduction to DNA (6 of 13)
  • The double helix each DNA molecule has two
    polynucleotide chains wound around each other
    like a spiral staircase
  • The phosphatesugar backbone represents the
    handrails
  • Pairs of bases linked together by hydrogen bonds
    represent the steps
  • Hydrogen bonds hold the two chains together under
    normal physiological conditions

30
Introduction to DNA (7 of 13)
  • DNA
  • Carries the information needed for making and
    maintaining the different parts of an organism
  • Chromosomes
  • Consist of DNA in the nuclei of cells coiled
    around proteins (histone molecules)
  • Humans have 46 chromosomes, 23 from each parent
  • Genes
  • Are segments of DNA molecules that control the
    production of different proteins in an organism
  • Vary in terms of the number and sequence of base
    pairs they contain

31
Introduction to DNA (8 of 13)
  • Cell replication
  • Before a cell divides, the double helix strand
    begins to unwind.
  • Each unwinding strand serves as a template for
    the formation of a new complementary strand.
  • Nucleotides are attracted to the exposed bases
    and become hydrogen-bonded to them A to T, T to
    A, C to G, G to C.

32
Introduction to DNA (9 of 13)
  • Ribonucleic acid (RNA)
  • Primary structure is similar to DNA
  • Ribosephosphoric acid units form backbone
  • Each ribose unit is bonded to one of the four
    bases
  • Protein synthesis a series of complex steps
    involving RNA
  • Transcription
  • Translation

33
Introduction to DNA (10 of 13)
  • Protein synthesis transcription
  • A single strand of RNA is synthesized inside the
    cell nucleus.
  • A segment of the DNA double helix separates into
    single strands.
  • The exposed bases of one strand act as the
    template for the synthesis of an RNA molecule.
  • The base sequence (messenger RNA) complements the
    base sequence on the DNA strand with one
    exception RNA transcribes a uracil instead of a
    thymine to adenine.

34
Introduction to DNA (11 of 13)
  • Protein synthesis translation
  • The code that has been copied to the new protein
    is interpreted.
  • mRNA leaves the nucleus and takes its chemical
    message to the cytoplasm of the cell, where it
    binds with ribosomes.
  • Guided by the first codon on the mRNA strand, a
    transfer RNA molecule with an anticodon that is
    complementary to this codon transports a specific
    amino acid to the mRNA codon

35
Introduction to DNA (12 of 13)
  • Protein synthesis
  • The actual protein synthesis occurs in the
    ribosomes, which move along the mRNA one codon at
    a time as the amino acid chain grows.
  • The mRNA is read codon by codon and the protein
    is built up one amino acid at a time in the
    correct sequence.

36
Introduction to DNA (13 of 13)
  • The genetic code
  • Each three-base sequence in mRNA codes for a
    specific amino acid
  • 64 three-base codons can be formed from the four
    bases in mRNA

37
Nuclear DNA and the Law (1 of 2)
  • 1985 routine analysis of the structure of human
    genes led to the discovery that portions of the
    DNA structure are as unique to each individual as
    fingerprints
  • 1987 individuals were first convicted of rape
    based on DNA evidence (in both the United States
    and the United Kingdom)

38
Nuclear DNA and the Law (2 of 2)
  • State v. Woodall the court accepted the results
    of DNA testing, but ruled that the inconclusive
    results failed to exculpate Woodall
  • Spencer v. Commonwealth admission of DNA
    evidence led to guilty verdicts resulting in the
    death penalty for the defendant
  • People v. Castro the court required laboratories
    and personnel to follow appropriate practices and
    prove the validity of their procedures before DNA
    evidence would be accepted in court
  • DNA testing is generally accepted as admissible
    under Frye or Daubert standards

39
Mitochondrial DNA
  • Mitochondria
  • Provide 90 of the bodys energy
  • Contain DNA that can be used for testing purposes
  • Mitochondrial DNA (mtDNA)
  • Is circular and much smaller than nuclear DNA
  • Is inherited from the mother
  • State of Tennessee v. Ware (1996) first use of
    mtDNA in court to match hair samples at the crime
    scene to the suspect
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