Lecture: Forensic Serology Serology: the medical science dealing with serums. Serum: the clear yellowish fluid obtained when whole blood isseparated into its solid and liquid components. Forensic serologists: scientists who examine physical evidence with the intent of finding, identifying and individualizing stains of biological origin.

Definitions Blood: suspended in the blood are solid materials, including red blood cells (erythrocytes), white blood cells (leukocytes) and platelets. Antigens: chemical structures attached to the surfaces of red blood cells. Antibodies: proteins floating in the serum that exist because people have allergies or may have come in contact with a common disease (TB, smallpox, and hepatitis are common antibodies). A basic principle of serology is that for every antigen, there exists a specific antibody. In fact, ALL BLOOD GROUPS ARE DEFINED BY THE ANTIGENS ON THEIR RED BLOOD CELLS AND ANTIBODIES IN THEIR SERUM.

Blood Typing & Distribution Blood type Antigens on Red cells Antibodies in Serum A Anti-B B Anti-A AB Neither anti-A or anti-B O Both anti-A and anti-B For routine blood typing, all you need are two antiserums: anti-A and anti-B, both easily available commercially. By dripping a droplet of these antiserums in samples of blood, you see which samples maintain a normal appearance (at about 200x magnification) and which samples become clotted, or agglutinated. Blood of type A will be agglutinated by anti-A serum; blood of type B will be agglutinated by anti-B serum; AB blood by both; and O blood by neither. You are essentially determining blood type by injecting the worst possible poison into someone's blood sample to see what happens. O A B AB 43-45% 40-42% 10-12% 3-5% O+ 39% O- 6% A+ 35% A- 5% B+ 8% B- 2% AB+ 4% AB- 1%

You are essentially determining blood type by injecting the worst possible poison into someone's blood sample to see what happens.

Blood Enzymes and Proteins Enzymes: proteins that have important functions in regulating the body’s chemistry. Enzymes have the characteristic of existing in different forms (polymorphic) and can be separated into protein components called iso-enzymes. A common polymorphism is Hb, which causes sickle-cell anemia. Iso-enzymes can be separated by electrophoresis. Forensic serologists have studied these iso-enzymes with the goal of being able to individualize blood samples found at crime scenes. While there are many iso-enzymes in blood, only those that survive the drying and aging process are useful to the forensic serologist.

Iso-enzymes and Probability Each of these protein and enzyme variants, as well as all blood subtypes, have known distributions in a population. It's therefore a simple matter to calculate probability estimates that border on individualized blood typing. Probability is defined as the frequency of an event occurring. If there are several event that may occur, the overall probability will be the product of these probabilities. Probability is usually expressed in per cent (i.e., 25%), while the frequency of an event is expressed as a decimal value (i.e., 0.25) At a crime scene, a blood sample and the suspect’s blood had the following characteristics: A blood (42%), basic subtype A2 (25%), protein AK (15%) and enzyme PGM 2 (6.0%). What is the frequency of occurrence of these blood characteristics in the general population? Answer: 0.00094 (0.42 X 0.25 X 0.15 X 0.06) or 0.094% probability!

BLOODSTAIN CHARACTERIZATION Bloodstain analysis traditionally follows the following steps: Is the stain blood? Is the stain animal or human blood? If human blood, what type? Can the sex, age, and race of the source of blood be determined? The benzidine test was long used until replaced by the Kastle-Meyer test. Both tests are color tests based on the observation that hemoglobin will oxidize several classes of organic compounds. While Kastle-Meyer is not a specific test for blood, the other materials that will cause a pink color change are unlikely to be found at crime scenes.

BLOODSTAIN CHARACTERIZATION Is the stain blood? Another test used is a Hemastix® strip, which will turn green in the presence of blood. Luminol is an important presumtive identification test for blood. The iron in hemoglobin reacts with the luminol and causes the emission of light (luminescence).

BLOODSTAIN CHARACTERIZATION Is the stain animal or human blood? To answer Question 2, forensic serologists use antiserum tests. The standard test is called the precipitin test This involves forming antibodies to human blood in an animal. The animal serum thus treated will cause a precipitate to form when reacted with human blood.

Blood Stain Patterns Information Obtained: Origin of bloodstains Distance between point of impact and origin Type and direction of impact Object/weapon used Minimum number of blows Position of victim, offender, and objects Movement by victim or offender at scene Support/contradict witness statements Indicate staged/secondary scenes

Blood Stain Patterns Cast-off Stains

Blood Stain Patterns Drip patterns

Blood Stain Patterns Swipe

Blood Stain Patterns Wipe

Blood Stain Patterns Effects of Surface Texture Horizontal drop creates circular pattern Forces of surface tension Rougher surface = greater distortion The angle of impact can be calculated in two ways: The length to width ratio can be calculated, then that value is compared to a standard curve to determine the angle of impact. Alternatively, the arc sin of the width to length ratio can be calculated to give the angle of impact.

Blood Stain Patterns Impact Angles Defined as the internal angle at which blood strikes a target surface Greater angle = greater elongation Determine direction of travel

Blood Stain Patterns Calculating Impact Angle Determine L/W ratio Determine W/L ratio Use calculator or standard curve

Blood Stain Patterns Point of Origin The point of origin is essentially the location from which the blood that produced certain bloodstains originated. POO is a common point where multiple individual bloodstains can be traced. Lines are drawn through the long axis of the individual bloodstains, and the point where those lines converge is determined to be the point of origin.

Principles of Heredity Transmission of Traits Accomplished by genes, which is the basic unit of heridity. 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. 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.

Principles of Heridity 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.