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Chapter 8 Blood & Blood Splatter By the end of this chapter you will be able to:

• explain the composition of blood • describe the function of blood cells • determine the blood type of a blood sample • conduct a blood splatter analysis • examine wounds and describe the nature of the weapon • find and process blood evidence

Introduction

• Blood typing is class evidence; whereas DNA profiling (using white blood cells) is individual evidence. • A blood splatter pattern can give information about the truthfulness of an account by a witness or a suspect.• It can provide info about the direction from which the blood originated, the point of origin, the angle and velocity of impact, and type of weapon used. • Our understanding of blood began in ancient times and continues to grow today.

History

• 2500B.C.: Egyptian bloodletting­effort to cure disease• 500B.C.: Greeks discovered difference between arteries and veins• 1659: Leeuwenhoek saw blood cells w/ microscope• 1901­1902: blood types discovered• 1940: Rh protein discovered• 1959: Congo­first recorded case of AIDS• 1984: HIV identified as cause of AIDS

Composition of Blood

• Blood is a circulating tissue• Whole blood carries cells and plasma—the fluid with hormones, antibodies, clotting factors, and nutrients.

­ plasma is similar to salt water in composition • Red blood cells (erythrocytes) carry oxygen to the body’s cells and carbon dioxide away.

­ Hemoglobin binds & transports O2, makes blood red• White blood cells (leukocytes) fight disease and foreign invaders and are only ones that contain nuclei & DNA. • Platelets aid in blood clotting and the repair of damaged blood vessels.

Blood Typing—Proteins

42% 12% 3% 43% of the population in the United States (of which 85% is Rh+)

• Blood typing is quicker and less expensive than DNA profiling. • It produces class evidence but can still link a suspect to a crime scene or exclude a suspect.

Discovery of Blood types

• 1900 Landsteiner found that blood from one person did not always mix with blood from another

­ clumping might occur which could result in death• The presence or absence of particular cell­surface proteins found embedded within the cell or plasma membranes of red blood cells determine a person's blood type• An antibody reaction test is used to identify each blood type

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A and B Proteins

• If a person's blood contains only protein A, then he/she has type A blood (same is true for type B)• If a person has neither A or B proteins, then he/she has type O blood. If person has both A and B, then he/she has type AB blood.

Genotype Blood TypeAA or AO ABB or BO B

AB ABOO O

Rh Factor

• In 1940, Weiner worked with Rhesus monkeys and discovered another protein on red blood cells• 85% of humans have the Rh protein (factor) and are designated as Rh+• Blood types are typically defined by the presence or absence of the A, B and Rh proteins.• When a person receives a blood protein that is foreign to him or her, antibodies will cause the blood to clump and may cause death.

Blood Typing—Antibodies; Additional Proteins and Enzymes

• B­lymphocytes are specialized white blood cells that secrete antibodies• Antibodies ­ proteins secreted by white blood cells that attach to specific antigens to destroy them. • Antigens ­ foreign molecules or cells that react to antibodies. • Antigen­antibody response White blood cells recognize a substance as foreign and try to destroy it• B lymphocytes makes antibodies against the foreign blood protein which attach to the foreign blood cells• Phagocytes,a type of white blood cell, engulfs it

AB­

AB+

AB­

A+

A­

B+

B­

O+

O­

Blood Typing ­ Agglutination

• Agglutination ­ clumping of molecules or cells caused by an antigen­antibody response• Each red blood cell has more than 1 million protein binding sites and there are more than 300 known blood group proteins, such as M and N proteins.• Antibodies are Y­shaped and each arm of the Y attaches to a different red blood cell when it recognizes a foreign protein causing the cells to clump together• If clumping occurs within a person, the blood flow is blocked

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Blood Typing ­ Tests

• Blood is tested for A, B and Rh proteins• Three tests are performed.

­ Blood is mixed with antibodies that bind to each of the three proteins.

­ If blood clumps (agglutinates) when mixed with the antibodies for protein A, that means the person's blood contains protein A.

­ B and Rh are tested the same way­ People with type AB+ would have clumps with all

three tests. O­ would not clump with any test

Blood Typing—Probability and Blood Types

• Since we know frequency of different genes, it is possible to determine the probability that a particular blood type will appear in a particular population. • To determine the probability of two separate events, we multiply their individual probabilities. • By identifying the additional proteins in the blood evidence sample, investigators can limit the size of a suspect population and help identify a suspect.