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Testing for Blood.

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Presentation on theme: "Testing for Blood."— Presentation transcript:

1 Testing for Blood

2 Presumptive Tests for Blood Determination
Kastle-Meyer color test—a mixture of phenolphthalein and hydrogen peroxide; the hemoglobin will cause the formation of a deep pink color if blood is present Hematest tablet—reacts with the heme group in blood, causing a blue-green color Luminol test—reaction with blood to produce light

3 Human versus Animal Blood
Microscopic observation Precipitin test—blood is injected into a rabbit; antibodies are formed; the rabbit’s blood is extracted as an antiserum; the antiserum is placed on sample blood. The sample will react with human proteins if human blood is present. This test is very sensitive and requires only a small amount of blood.

4 Animal Blood Larger nucleic red blood cells Frog blood

5 Luminol with false positive (bleach)
Testing for Blood A positive result from the Kastle-Meyer color test is highly indicative of blood. Hemoglobin causes a deep pink color. Alternatively, the luminol test is used to search out trace amounts of blood located at crime scenes. Luminol produces light (luminescence) in a darkened area. Courtesy of C. Fanning Luminol with false positive (bleach) Courtesy of C. Fanning Courtesy of C. Fanning

6 Testing for Blood Microcrystalline tests, such as the Takayama and Teichmann tests, depend on the addition of specific chemicals to the blood so that characteristic crystals will be formed. Cont.

7 Testing for Blood Once the stain has been characterized as blood, the precipitin test will determine whether the stain is of human or animal origin.

8 Testing for Blood The precipitin test uses antisera normally derived from rabbits that have been injected with the blood of a known animal to determine the species origin of a questioned bloodstain. Once it has been determined that the bloodstain is of human origin, an effort must be made to associate or dissociate the stain with a particular individual. DNA analysis has allowed forensic scientists to associate blood to a single individual.

9 Heredity and Paternity
The transmission of hereditary material is accomplished by means of microscopic units called genes, located on chromosomes. Alternative forms of genes that influence a given characteristic (such as eye color or blood type) are known as alleles. Paternity testing has historically involved the A-B-O blood typing system, along with blood factors other than A-B-O. Currently, paternity testing has implemented DNA test procedures that can raise the odds of establishing paternity beyond 99 percent.

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