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Forensic Serology

Forensic Serology

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Forensic Serology

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  1. Forensic Serology Criminalistics Chapter 12

  2. Karl Landsteiner • First person to recognize that all human blood is not the same • Blood is distinguishable by its’ group or type • Now called the A-B-O System • Important because using the wrong blood cause instant death for those receiving transfusions • Today there are more than 100 different blood factors known

  3. Blood as Identification • In theory, no two individuals, except for identical twins, could have the same combination of all individual blood factors (not just blood types) • Blood factors are controlled genetically and have the potential of being a distinctive feature for personal identification • Important in serious crimes where blood is found at a crime scene—homicides, assaults, and rape.

  4. Blood as Evidence • Blood typing not so useful anymore because of DNA technology • Scientists can now characterize biological evidence by selecting regions of our DNA

  5. The Nature of Blood • Blood: complex mixture of cells, enzymes, proteins, and inorganic substances • Plasma: the fluid portion of blood • Mostly water • 55% of blood content • The other 45% is made of solid particles

  6. The Nature of Blood • Erythrocytes: red blood cells; found in plasma • Leukocytes: white blood cells; found in plasma • Platelets: clotting factor; found in plasma • Serum: the liquid that separates from the blood when a clot is formed

  7. Important Parts for Forensic Science • Red Blood Cells—because of their importance in blood typing • Serum—because of its’ importance in carrying antibodies

  8. Red Blood Cells and Blood Types • Protein resides on the Red Blood Cell called antigens • Antigens give blood-type characteristics to the Red Blood Cells • ABO and Rh systems are the most important blood types

  9. Antigens and Blood Types • Type A Blood has Antigen A on the surface of the Red Blood Cell • Type B Blood has Antigen B on the surface of the Red Blood Cell • Type AB Blood has both Antigen A and Antigen B on the surface of the Red Blood Cell • Type O Blood has neither Antigen A nor Antigen B on the surface of the Red Blood Cell

  10. Distribution of Blood Types in US • Type O Blood is the most prevalent with 43% • Type A Blood is the next most common with 42% • Type B Blood is less common with 12% • Type AB Blood is the most rare type with 3%

  11. Rh Factor or D Antigen • Blood that contains the D Antigen is referred to as Rh + • Blood that does not contain the D Antigen is referred to as Rh -

  12. In routine blood typing, it is the presence or absence of the three antigens— A, B, D—that determines a person’s blood type.

  13. Fundamental Principle of Blood Typing • Serum contains proteins known as antibodies • For every antigen, there is a specific antibody that reacts against it. • Anti-A reacts against antigen A • Anti-B reacts against antigen B • When antibodies react against its’ specific antigen, agglutination or clumping of RBCs occur.

  14. Transfusions cont. Universal Acceptor Universal Donor

  15. What is Serology? • The term serology refers to a broad scope of laboratory tests that use specific antigen and serum antibody reactions. • Blood typing falls into this category.

  16. Forensic Characterization of Blood Stains • Important Questions: • Is it blood? • From what species did the blood originate? • If the blood is human, how closely can it be associated with a particular individual?

  17. Preliminary Determination of Blood • Sample tested with phenolphthalein • Turns deep pink color Positive for blood • Also known as the Kastle-Meyer Test • Use of Hemastix • When moistened with distilled water and placed in contact with stain, a bright green color indicates blood.

  18. Preliminary Determination of Blood • Luminol Test • Produces light if blood is present in a darkened area • Extremely sensitive: can detect stains diluted up to 300X • Will not interfere with any subsequent DNA testing

  19. Is it human blood? • Precipitin Test: • Human blood is inserted into animal (rabbit) • Rabbits produce antibodies to react against the human blood • Blood is drawn from rabbit that contains the human antibodiesproduces human antiserum • Unknown blood sample, if human, will react with the human antiserum from the rabbit by forming a precipitate

  20. Is it human blood? • Gel Diffusion and Electrophoresis • Antibodies and antigens will move toward each other on an agar gel plate or in an electrophoresis chamber • Forms a precipitate where the human antibodies and antigens meet • No precipitate? Unknown sample is not human blood

  21. Effectiveness of Tests for Human Blood • Precipitin Test: • Very sensitive and requires only a very small amount of blood • Works on very old samples • Even in washed items blood may be detected

  22. Stain Patterns of Blood • Important Factors: • Location of stains • Distribution of stains • Appearance of stains • All factors are important in interpreting and reconstructing the events of a crime scene.

  23. Blood Pattern Interpretation • Important Factors: • Surface Texture • Harder and less porous surfaces produce less spatter results • Direction of travel • Determined by the shape of the stain • Pointed end of stain always points in the direction of travel

  24. Blood Pattern Interpretation • Important Factors: • Angle of Impact • Right angle of impact produces a circular drop stain • As angle decreases, the blood drop becomes more elongated • Origin of Blood Spatter • Can be determined by drawing lines or connecting strings through blood stains

  25. Principles of Heredity • Antigens and enzymes are genetically controlled • Genes: responsible for transfer of hereditable material • Genes are found on chromosomes, which are found in the nucleus of every cell

  26. Principles of Heredity • Human Cells contain 46 chromosomes with the exception of the egg and sperm, which contain only 23. • 23 of these chromosomes are inherited from mother • 23 of these chromosomes are inherited from father

  27. Sex Chromosomes • X-Chromosome: Female Sex Chromosome • Y-Chromosome: Male Sex Chromosome • XX individuals are female • XY individuals are male

  28. Genes Come in Pairs • The position a gene occupies on a chromosome is called a locus. • Genes for the same trait are located at the same locus on both the mother and the father’s chromosomes.

  29. Genes Come in Pairs • Alternative forms of genes that influence a given characteristic are called alleles. • Father: allele for brown eyes • Mother: allele for blue eyes

  30. Gene Pairs • Made up of two similar genes • AA: Homozygous • “Homo” means the same • Aa: Heterozygous • “Hetero” means different

  31. Blood Types are Genetic • A and B Blood Types are Dominant • Dominant: Characteristic is shown • Blood Type O is Recessive • Recessive: Characteristic is hidden • Recessive characteristics only appear when both alleles are recessive • Homozygous recessive OO

  32. Phenotype V. Genotype • Phenotype: individual’s outward characteristics • Genotype: individual’s pair of allele genes together • Example: • PhenotypeGenotype Type B Blood Could be BO or BB depending on parents

  33. Alleles for Blood Types • Type A allele- A • Type B allele- B • Type O allele- O

  34. Therefore….. • A person with the phenotype of Type A must have a genotype of AA or AO • A person with a phenotype of Type B must have a genotype of BB or BO • A person with a phenotype of Type AB must have a genotype of AB • A person with a phenotype of Type O must have a genotype of OO

  35. Punnett Squares • Mother: AB Father: BB B B A Genotype of a child with Type B Blood must be BB B

  36. Paternity Tests • No blood group can be present in a child without being present in one of the parents • Paternity tests can be resolved in this way unless disputed fathers have the same blood type • Paternity tests can also be determined by using DNA testing

  37. Forensic Characteristics of Semen • Normal male can ejaculate 2.5-6 ml of seminal fluid • Each ml contains 100 million or more spermatozoa

  38. 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

  39. 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

  40. 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

  41. 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

  42. Medical Examination of Suspect • All clothing • Pubic hair combings • Pulled head and pubic hairs for reference samples • Penile swab • Blood sample or buccal swab