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Testing for Blood

Testing for Blood. 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

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Testing for Blood

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  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. 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 TakayamaandTeichmann 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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