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Forensic Serology

Forensic Serology. Criminalistics Chapter 12. 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

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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. 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.

  15. 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?

  16. 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.

  17. 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

  18. 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

  19. 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

  20. 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

  21. 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.

  22. 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

  23. 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

  24. 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

  25. 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

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

  27. 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.

  28. 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

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

  30. 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

  31. 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

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

  33. 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

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

  35. 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

  36. 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

  37. 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

  38. 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

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

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