Blood Blood Spatter, Lecture notes of Genetics

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Blood

Blood Spatter

Blood Evidence

• Class evidence
  • more than one person has the same blood

type

• Individual evidence
  • DNA in white blood cells can be used for

a DNA profile

Blood

• Fluid tissue that makes up 8% of human

body weight

• Females: 4-5 L
• Males: 5-6 L
• Composed of plasma and formed

elements

Composition of Blood

• Plasma
  • 90% water
  • 10% dissolved proteins, nutrients
• Blood cells
  • Red blood cells (erythrocytes)
    • Carry oxygen and carbon dioxide
    • Hemoglobin: iron containing pigment
  • White blood cells (leukocytes)
    • Fight disease, foreign invaders
  • Platelets (thrombocytes)
    • Blood clotting

Properties of blood

Water Blood Viscosity 1.0 mP·s

• 1 3 - 4 mP·s - 1 Surface tension 0.073 N·m
• 1 0.058 N·m
• 1 Density 1000 kg/m 3 1060 kg/m 3

Blood Typing

• Cells have antigens on the surface of the cell membrane identifying them. - body’s ability to differentiate self and non-self (foreign invaders) - allows immune system to function to protect body
• Blood cells have a different set of antigens on the surface - antigens are determined by genes - presence or absence of red blood cell antigens are the basis of blood groups

Blood Groups

• Agglutination: clumping of red blood cells
  • occurs when blood cells encounter antibodies
  • example: Anti-A antibodies cause type A cells to agglutinate (clump)
• Discovery of antigens and antibodies on red blood cells led identification of blood groups - allowed for blood transfusions to occur successfully when blood types could be identified

Blood Groups

• A, B, Rh antigens most important blood antigens
• Blood Types: A, B, AB, O.
  • O is universal donor
  • AB is universal recipient
• Plasma contains antibodies to react with antigens other than own - type A contains anti-B antibodies - type B contains anti-A antibodies - anti-A and anti-B antibodies are produced before birth, unlike other antibodies
• Rh factor: first discovered in Rhesus monkeys
  • • if antigen present
  • • if antigen not present
    • anti-Rh antibodies are not produced until exposed to Rh
      • blood

Blood Transfusions

• Each blood type can give to another of the same blood type. - no antibodies to interfere with antigens on RBCs
• Blood of one type can be given to a different type only if antibodies are compatible
• Type O: universal donor
  • no antigens on O blood cells to be attacked by A or B antibodies
• Type AB: universal recipient
  • no A or B antibodies to attack donor cells
• Rh
  • can only give to other + blood types, but can receive + or – blood type

• Rh

   can give to + or **–** blood types, but can only receive **–** blood 

  type

Blood Type

42% 12% 3% 43% of the population in the United States

Blood Typing

• Quicker, less expensive than DNA profiling
• Class evidence
  • More than one person has the same blood type
  • Typing blood can link a suspect or exclude a suspect, but does not prove guilt
• Blood type could eliminate a suspect with the wrong blood type, but could not confirm a suspect (if more than one have that blood type)

Blood Spatter Analysis

blood-spatter pattern: grouping of bloodstains

Blood Spatter

• Grouping of bloodstains
• Spatter can be used to help recreate crime scene - Validates witness statements - Can be used to determine: - Direction from which blood originated - Angle of impact - Point of origin of blood - High or low velocity impact - Can indicate type of weapon used

Blood Spatter

• Blood droplet has a tendency to elongate as it falls due to gravity - cohesive forces resist droplet flattening - Satellites: any blood that overcomes cohesion and separates from main droplet will form small secondary droplets - satellites separate from main droplet - Spikes or extension may form if blood lands on a porous surface such as wood - spikes are attached to main droplet