Lesson Sampling

Topic: Blood Typing

Grades: Middle school

Duration: Three ‘60 minute’ periods (to be adapted to own site)

Overview

In this activity, students will perform a simulated test for the presence of blood and then use blood typing of synthetic blood to test whether a suspect can be linked to a crime. The methodology used in this activity simulates that which would be used in an actual crime setting, however, no actual blood or blood products are used in conducting this activity which eliminates any risk associated with exposure to actual blood or blood products. All materials are safe to dispose of by ordinary means.

Goals:

1. To introduce concepts to help understand the importance and function of DNA.

2. To demonstrate to students how genetics relates to forensic evidence.

3. To introduce students to the basic human blood types.

Objectives:

1. Students will be able to understand and describe how genetics is important in a forensic investigation.

2. Students will be able to list the four major human blood types.

3. Students will be able to identify the correct suspect by conducting a forensic investigation.

Background:

Blood is an important fluid in the body that has many functions including the transportation of nutrients and oxygen to our vital organs and cells. It also helps keep the body system free of toxins by transporting carbon dioxide and waste out of the body.

Our blood is a highly specialized tissue composed of many different parts. Blood is composed of red cells, white cells, platelets, and plasma. All humans produce these blood components and there are no population or regional differences in the composition however there are population and regional differences in the types of antigens that an individual possesses on the surface of their red blood cells.

A scientist by the name of Karl Landsteiner was awarded a Noble prize in 1930 for his discovery of human blood groups. This observation resulted in the establishment of blood typing based upon the antigen found on the red blood cell surface. Landsteiner observed two distinct chemical molecules present on the surface of the red blood cells. He labeled one molecule "A" and the other molecule "B." If the red blood cell had only "A" molecules on it, that blood cell was called type A. If the red blood cell had only "B" molecules on it, that blood cell was called type B. If the red blood cell had a mixture of both molecules, that blood cell was called type AB. If the red blood cell had neither molecule, that blood cell was called type O.

From these discoveries, the four blood groups have been established as A, B, AB, and O. The chemical markers Landsteiner discovered on the surface of the RBCs are antigens. An antigen- is a protein marker on the surface of the type-A and type-B and typeAB red blood cells. When an A blood transfusion occurs in a person with the wrong blood type, antibodies in the plasma of the transfused person react with antigens on the donated blood. This causes immediate or delayed agglutination (clumping of blood cells) and hemolysis (destruction of red blood cells), which could possibly result in death of the transfused person. Blood donors and recipients must be typed and matched very carefully before transfusions are given. Antigens are inherited from ones parents.

The Rhesus factor

While studying Rhesus monkeys, Scientists discovered a blood protein that caused slow agglutination after massive exposure such as a result of having a major blood transfusion or by a mother having a baby.

If your blood cell does contain the protein, your blood is said to be Rh positive (Rh+). If your blood does not contain the protein, your blood type would be Rh negative (Rh-)

When your blood is typed you are given your antigenic blood type and your positive or negative result for the Rh factor. Thus an AB+ blood type means that you have both antigens with a positive Rh factor.

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