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FORENSIC SCIENCE

Serology

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Blood Characteristics• Plasma--fluid portion of the blood (55%)

• Cells (45%)– Erythrocytes--red blood cells; responsible for oxygen distribution

– Leukocytes--white blood cells; responsible for “cleaning” the system of foreign invaders

– Thrombocytes--platelets; responsible for blood clotting

• Serum--liquid that separates from the blood when a clot is formed

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Blood Terminology

• ABO blood groups--based on having an A, B, both or none of the factors on the red blood cell

• Rh factor--may be present on the red blood cell; positive if present and negative if not

• Antigen--a substance found on a red blood cell

• Antibody--a substance that reacts with an antigen

• Agglutination--clumping of red blood cells; will result if blood types with different antibodies are mixed

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Blood Genetic Terminology

• Genotype--letters that represent different versions (alleles) of the same gene; ex: AA, AO, BO, BB, AB and OO

• Phenotype--words that describe the traits, physical result of genotype; ex: A, B, O

• Heterozygous--different alleles for the same trait; ex: AO, BO, AB

• Homozygous--the same alleles for the trait; ex: AA, BB, OO

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Forensic Blood AnalysisQuestions to be answered:• Is it blood?• Is it human blood?• Whose is it?

– Determine blood type, alcohol content, drugs present

– Determine the method(s) in which blood may have been deposited

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Presumptive Tests for Blood

• Kastle-Meyer color test--a mixture of phenolphthalein and hydrogen peroxide is tested on the unknown liquid or dry stain– Positive Result: the blood’s hemoglobin will cause the formation of a deep pink color

• Leucomalachite test--leucomalachite green mixed with acetic acid and distilled water– Positive Result: An additional drop of sodium percblorate will turn blood green and then darken.

• Luminol test--reaction with blood results in the production of light

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Human vs Animal• Microscopic survey• Precipitin test--blood is injected into a rabbit; antibodies are formed; rabbit’s blood is extracted as an antiserum; the antiserum is placed on sample blood. It will react with human proteins. This test is very sensitive and requires only a small amount of blood.

• Characteristic Differences

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Animal Blood

Frog Blood• Larger nucleic red blood cells

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Human Blood• Red blood cells--5 to 6 million per mm3, no nucleus

• White blood cells - Larger but less numerous, 5 to 10,000 per mm3

• Platelets - Tiny, cellular fragments 350 to 500,00 per mm3

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Blood Typing• A blood type has antigen A and will agglutinate with B.

• B blood type has antigen B and will agglutinate with A.

• AB blood type has antigens A and B and will not agglutinate with either A or B.

• O blood type has neither antigen A or B and will agglutinate with either.

Blood Groups

Type Antigen Antibody Can GiveBlood To:

Can GetBlood From

A

B

AB

O

A

B

A and B

NeitherA nor B

B

A

NeitherA nor B

A and B

A, AB O, A

B, AB O , B

AB

A, B, O, AB

A, B, O, AB

O

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Blood Reactions to Antiserum

REACTION

BLOOD TYPEAnti-A Serum Anti-B Serum

Agglutination

No agglutination

Agglutination

No agglutination

No agglutination

Agglutination

Agglutination

No agglutination

Type A

Type B

Type AB

Type O

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Population Distribution

of Blood Types in the U. S. Type Percent

O

A

B

AB

45

39

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4

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BLOOD PATTERN/SEROLOGICAL

RECONSTRUCTIONSCENE PATTERNRECONSTRUCTION1. Stain condition

2. Pattern3. Distribution4. Location5. Directionality

LAB RESULTS RECONSTRUCTION

1. Genetic marker typing

2. Age Determination3. Source Determination

4. Race Determination

5. Sex DeterminationFrom “Cracking Cases” by Dr. Henry C. Lee

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BLOOD DROPLETCharacteristics

• A blood droplet will remain spherical in space until it drops onto a surface

• Once a blood droplet impacts a surface, a bloodstain is formed.

• A droplet falling from the same height, hitting the same surface at the same angle, will produce a stain with the same basic shape.

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CONDITIONS AFFECTINGBLOODSTAIN SHAPE

• Size of the droplet• Angle of impact• Velocity at which the blood droplet left the original surface

• Texture of the target surface– On clean glass or plastic--droplet will have smooth outside edges

– On a rough surface--will produce scalloping on the edges

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Questions Answered by Blood Spatter Interpretation

• The distance between the target surface and the origin of blood at the time of blood shed

• The point(s) of origin of the blood• Movement and direction of a person or an object

• The number of blows, shots, etc. causing the bloodshed and/or the dispersal of blood.

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Questions Answered by Blood Spatter

Interpretation • Type and direction of impact that produced the bloodshed

• The position of the victim and/or object during bloodshed

• Movement of the victim and/or object after bloodshed

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Bloodstain Terminology• Angle of impact--angle at which blood strikes a target surface.

• Bloodstain transfer--When a bloody object comes into contact with a surface and leaves a patterned blood image on the surface.

• Backspatter--blood that is directed back toward its source of energy.

• Cast-off--blood that is thrown from an object in motion

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Bloodstain Terminology• Contact stain--general term referring to bloodstains caused by contact between a wet, blood-bearing surface and a second surface which may or may not have blood on it– Transfer--image is recognizable and may be identifiable with a particular object

– Swipe--wet blood is transferred to a surface which did not first have blood on it

– Wipe--a non-blood bearing object moves through a wet bloodstain, altering the appearance of the original stain

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Bloodstain Terminology• Directionality--relates to the direction a drop of blood traveled in space from its point of origin

• Terminal velocity--the greatest speed to which a free falling drop of blood can accelerate in air. It is dependent upon the acceleration of gravity and the friction of the air against the blood--approximately 25:1 feet/second.

– High velocity--greater than 100 feet per second; gives a fine mist appearance

– Low velocity--5 feet per second or less– Medium velocity--5 to 25 feet per second.

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Bloodstain Pattern

• Terminal Velocity

• Directionality• Angle of Impact

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Blood Stain Patterns

The shape of a blood stain: Round--if it falls straight down at a 90 degree angle.

Elliptical--Blood droplet elongates as the angle decreases from 90 to 0 degrees. The angle can be determined by the following formula:

width = sine of the impact angle

length

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IMPACT• The more acute the angle of impact, the more elongated the stain.

• 90 degree angles are perfectly round with 80 degree angles taking on a more elliptical shape.

• At about 30 degrees the stain will begin to produce a tail.

• The more acute the angle, the easier it is to determine the direction of travel.

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Blood Stains• The harder and less porous the surface, the less the blood drop will break apart.

• The softer and more porous the surface, the more a blood drop will break apart.

• The pointed end of the blood stain faces the direction the stain is traveling.

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Area of Intersection

The location of the blood source can be determined by drawing lines the various blood droplets to the point where they intersect. This is the blood’s origin.

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Area of ConvergenceThe area of convergence is the point of origin; the spot where the “blow” occurred.

It is determined by drawing a line from the area of intersection straight up to where to where the angle of impact would intersect

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CRIME SCENE

What evidence can you see in this crime scene? What story does the scene tell?

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Bring In The Dogs!The dog

locates human scent. A closer look shows that the ashes have human remains and clothing. In addition, look closely at the rocks on the next slide.

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Blood Evidence

• Class evidence for blood would include blood type. If you can determine the DNA you would have individual evidence.

• Blood stain patterns are considered circumstantial evidence in a court room. Experts could argue many points including direction of stains, height of the perpetrator, position of the victim, left/right hand, whether the body was moved, etc.

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Sperm• Among the smallest and most highly specialized cells in the human body.

• Has a head and a tail• Contains 23 chromosomes with the genetic material found in the head

• Males release 2.5 to 6 milliliters of seminal fluid per ejaculation with approximately 100 million sperm per milliliter.

Magnified 400X

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SemenDetermination of Seminal Fluid• Acid phosphatase color test

– the presence of acid phosphatase, the enzyme secreted by the prostate gland into the seminal fluid, will turn purple when sodium alpha naphthylphosphate and Fast Blue B solution are placed on it.

– It will also fluoresce under UV light when it comes in contact with 4-methyl umbelliferyl phosphate.

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Semen (cont.)Determination of Seminal Fluid• Prostate Specific Antigen (PSA) or p30--unique to seminal plasma– P30 is isolated and injected into a rabbit where antibodies are produced (anti-p30)

– The stain extract is place in one well of an electrophoresis plate and the anti-p30 in the opposite well. The electric is applied and the antigens and antibodies move toward each other. The formation of a precipitation line between the wells shows the presence of p30 in the sample stain. It must be seminal fluid.

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Secretors• 80% of people are considered secretors. Their blood-type antigens are found in high concentration in their body fluids such as saliva, semen, vaginal secretions and gastric juice. If you are a secretor, you will have a higher concentration of A and B antigens than does your blood!!

• With the advent of DNA, the secretor evidence is not as important as it once was.