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Lecture: Blood and DNA Evidence

Lecture: Blood and DNA Evidence. DNA evidence . Blood at a Crime Scene: Some chemicals produce light when blood is present other will change colors. Classifying Blood into 4 types: A, B AB, and O. The antibodies in blood can be used to classify blood as either (+) or (-).

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Lecture: Blood and DNA Evidence

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  1. Lecture: Blood and DNA Evidence

  2. DNA evidence

  3. Blood at a Crime Scene: Some chemicals produce light when blood is present other will change colors.

  4. Classifying Blood into 4 types: A, B AB, and O. The antibodies in blood can be used to classify blood as either (+) or (-).

  5. Blood groups are named after the marker molecules found on the surface of red blood cells • Marker molecules act as “tags” letting the body know those cells are part of your body • Some people only have A marker molecules – type A • Some people only have B marker molecules – type B • Some people have both A and B markers – type AB • Some people have neither marker – type O ABO BLOOD GROUPS

  6. Are molecules that bind to the A or B marker molecules • Each antibody will bind to one specific molecule – this is how scientists used them to classify blood • Rh factor – Some people also have a marker molecule called the Rh factor • People with the Rh factor molecule are Rh + • People without the Rh factor molecule are Rh- CLASSIFICATION OF BLOOD USING Antibodies

  7. Results with Anti - A Results with Anti - B Which blood type is this? Type O

  8. Blood types are not like fingerprints. They can not be used to identify a suspect but instead they can point in the right direction. `

  9. Surface: - Hard surface will be a round shape. - Soft surface will have ragged edges. Angle of Impact: - 90°impact will be round. - Angled impact will be stretched out and loses its round shape. Blood stain patterns

  10. Generally the size of the drop decreases with the increase of the blow when it flies through the air or hits a surface. Size of drop

  11. The shape of the bloodstains can determine where the attack occurred. The tip of the stain always points in the direction that the blood had been moving. Direction of travel

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