WARM-UP Do you know your blood type? Have you ever donated blood? Have you ever received a blood transfusion or know someone who has? What do you think is the importance of blood typing in Forensic Science? What are you looking forward to in this unit, what are you dreading?

Identification Using Blood Groups Forensic Serology Identification Using Blood Groups

Forensic Serology Serology – term used to describe a broad range of laboratory tests using reactions of blood serum and body fluid The serology section of a forensic laboratory may deal with any or all of the following: blood typing characterization of unknown blood stain patterns for crime reconstruction paternity testing semen or saliva identification DNA techniques used for identification

Forensic Characterization of Bloodstains Three questions that must be answered by the forensic investigator: 1) Is it blood? Benzidine Test Kastle-Meyer Test Hemastix (o-tolidine, TMB) Luminol Test 2) Is it human blood? Precipitin Test 3) Can it be associated with an individual? Blood Type Testing (anti-serums)

Blood Antigens On the surface of red blood cells are chemical structures (proteins) called antigens The presence of antigens allow a living system to recognize foreign biological substances Antigens also impart specific characteristics to the red blood cells. These characteristics can be partly used to identify individuals Human red blood cells have more than 15 different antigen types that have been discovered

Blood Typing Blood typing involves determination of the antigens present on an individual’s red blood cells (RBCs) The two most common blood typing systems used are the A-B-O method and the Rh method type A blood – contain “A” antigen on RBCs type B blood – contain “B” antigen on RBCs type AB blood – contains both A and B antigens type O blood – contain no A or B antigens Rh+ blood – contain Rh antigen Rh- blood – no Rh antigen

Blood Typing Blood also contains antibodies – proteins that recognize and bind to certain, specific antigens Blood Type Antigens on RBC Antibodies A A anti-B B B anti-A AB AB none O none both A & B Rh Factor: A red blood cell that contains Rh antigens is said to be positive; no Rh antigens is said to be negative. The antibody is called “anti-D”

Blood Typing Red blood cells containing A antigens do not combine with B antibodies Red blood cells containing B antigens are clumped together (blood clot) in the presence of B antibodies

Blood Typing Human serum containing specific antibodies can be purchased Separately mix a drop of unknown blood sample with drop of each anti-serum Reaction between blood and anti-serum No reaction between blood and anti-serum

Blood Typing Example A sample of unknown blood is mixed with three anti-sera samples: Tube 1 (Anti-A): No reaction Tube 2 (Anti B): No reaction Tube 3 (Anti Rh): Cloudy reaction In terms of the A-B-O and Rh systems, what type blood is the sample? The ABO antigens are not confined to RBC; 80% of Americans are secretors, same antigens found on other cells O positive

Principles of Heredity – Vocabulary Review Gene: basic unit of heredity, consisting of a DNA segment located on a chromosome. Chromosome: a threadlike structure in the cell nucleus, along which the genes are located. Egg: female reproductive cell Sperm: male reproductive cell Zygote: cell arising from the union of an egg and a sperm cell X-chromosome: female sex chromosome (XX – female) Y-chromosome: male sex chromosome (XY – male)

Principles of Heredity – Vocabulary Review Allele: any form of a gene located at the same point on a particular pair of chromosomes Homozygous: a gene pair made up of two similar alleles (dominant/dominant AA & BB; recessive/recessive OO) Heterozygous: a gene pair made up of two different alleles (dominant/recessive AO & BO; co-dominant AB) Genotype: pair of allele genes in cell Phenotype: physical manifestation of a genetic trait (shape, color, blood type) Ex. Phenotype: Type A Genotype possibilities: AA or AO

Punnett Square Practice If a mother has type AB blood, and a father has type O blood, answer the following questions: What is the genotype of the mother and father? What are all the possible genotype combinations their offspring could have? Fill out the Punnett square below. A B O - 50% Chance offspring is Type A - 50% chance offspring is Type B AO BO

Paternity Testing in Forensics Genotyping of blood factors useful applications for transmissions of blood characteristics, but no direct relevance to criminal investigations Has implications in disputed-paternity cases (civil, not criminal cases) Resolved by comparing blood group genotypes of suspected parents and offspring. Does not always mean the suspect is the father, as many other males may also have the same blood type HLA (human leukocyte antigen) test looks at white blood cell antigens (90% accurate) DNA test procedures (over 99% accurate)

Punnett Square Practice Jane has type AB blood, and John has type O blood. If Jane’s child has type AB blood, is there a possibility that John is the father? A B O In the words of Maury Povich: “John… You are NOT the father” AO BO AO BO