Chapter 11; Blood

Serology; the study of bodily fluids

Separation of blood

• Living portion of blood is:• Erythrocytes (red blood cells…

RBCs)• Leukocytes (white blood cells)• Platelets

Liquid part of the blood with no cells in it is called the plasma.(Mostly water with salts, ions, proteins.)

BLOOD TRANSFUSIONS were not working!

OUTLAWED IN MOST COUNTRIES IN EARLY 1900’S

ABO Blood Typing

(Karl Landsteiner – 1901)

A classification of blood: A, B, AB, O

Rhesus monkey factor (Rh) discovered in 1940.If you have it, you’re Rh+ and if you don’t you’re Rh-

Theoretically, no two people have the same combination of blood factors and it should be possible to individualize evidence using blood, but in reality this is not the case.

Testing for every factor on RBCs in not practical, and many factors break down as blood dries and ages.

Blood is still important in forensics because testing can be done on both whole blood and dried bloodstains quickly and inexpensively.

ANTIGENS AND ANTIBODIES

Each antibody binds to a specific antigen; an

interaction similar to a lock and key.

The antibody destroysthe antigen

AGGLUTINATION

THE CLUMPING TOGETHER

OF RED BLOOD CELLS

Lattes slide

method

Uses antibody-antigen

reactionsto test for

blood types

Varies by country, ethnic group, etc.

Blood typing can be used to:

-show that two samples had different origins (exclude a suspect)

-determine the probability of an individual having a particular blood type

What is the probability that an American has type AB- blood?

4/100 x 15/100 = 60/10,000 or 0.6%

Blood Tests

Determines whether a substance is blood or not, but does NOT distinguish between human and animal blood. Hemastix test

LUMINOL TEST

LUMINESCES WITH BLOOD OR SEMEN

PRECIPITIN TEST

• Determines if blood is human

• An animal (mammal) is injected with sample. If human, animals produce antibodies.

Non-mammals

Oval red blood cells with a visible nucleus

Mammals

• Circular red-blood cells

• No nucleus

Secretors• 80 % of population• Blood type antigens

are secreted in bodily fluids (saliva, semen,

perspiration,gastric and vaginal secretions)

Blood enzymes

Proteins that regulate chemical reactions

Iso-enzymesProtein components into which enzymes can be separated

(1) PGM – an enzyme that has 10 variations

(2) importance- allows forensic scientists to reduce the number of possible sources

BLOOD SPATTER

SIZE AND SHAPE OF DROPSARE AFFECTED BY:

• HEIGHT OF FALL

• ANGLE OF IMPACT

• SURFACE ON WHICH THE DROPS LAND

Shape is determined by the impact angle

Determination of Impact Angle

Measure the length and widthof the stain

• Divide the width by the length to get arc sine of the impact angle

Width / Length = arc sine of impact angle

Ex: width = 2.4 cm

length = 3.1 cm

Ratio of width/length =

2.4 cm / 3.1 cm =

.77419

Use your calculator to get the impact angle

Enter:

“sin -1 (.77419)”

Answer:

50.7 degrees

50.7

Blood spatter labs

1. Height of drops vs. drop size

2. Angle of drop vs.

drop shape

3. Surface texture vs. drop size and shape

The Nobel Prize in Physiology or Medicine – Educational

(Blood type simulation)

American Justice; Jeffrey MacDonald