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Chapter 2: Sources of DNA Evidence. Forensic Biology by Richard Li. Introduction to Cells. DNA is located in cells which are the building blocks of the human body Two Types of cells: Sex Cells Somatic Cells. Introduction to Cells. Cell membrane Cytoplasm Nucleus.

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Presentation Transcript
introduction to cells
Introduction to Cells
  • DNA is located in cells which are the building blocks of the human body
  • Two Types of cells:
    • Sex Cells
    • Somatic Cells

Forensic Biology by Richard Li

introduction to cells1
Introduction to Cells
  • Cell membrane
  • Cytoplasm
  • Nucleus

Forensic Biology by Richard Li

examples of biological evidence
Examples of Biological Evidence
  • Blood
    • Most common type found at crime scenes
    • Consists of erythrocytes (red blood cells), leucocytes (white blood cells), and platelets
    • Nuclear DNA obtained from leucocytes

Forensic Biology by Richard Li

examples of biological evidence1
Examples of Biological Evidence
  • Hair
    • Consists of root and shaft
    • Medulla
    • Cortex
    • Cuticle
    • Grows at approximately 0.3mm per day
    • Anagen phase- growing phase
    • Catagen phase- follicle becomes inactive
    • Telogen phase- growth cycle ends

Forensic Biology by Richard Li

examples of biological evidence2
Examples of Biological Evidence
  • Hair as a source of DNA evidence
    • PCR allowed more productive analysis of hair
    • Formerly just analyzed morphology and comparisons
    • mtDNA can be isolated from roots and shafts
    • Nuclear DNA analysis or hair is preferred
      • Plucked hair with roots
      • Naturally shed hairs contain little nuclear DNA
      • Most hairs at crime scenes are naturally shed

Forensic Biology by Richard Li

examples of biological evidence3
Examples of Biological Evidence
  • Bone
    • Compact vs. Spongy
    • Osteocytes
    • Osteoblasts
    • Osteoclasts

Forensic Biology by Richard Li

examples of biological evidence4
Examples of Biological Evidence
  • Bone
    • Rate of degradation of human remains varies greatly with environmental conditions
    • Soft tissue is lost
    • Bones are more stable
    • Mass Fatalities-identify victims
    • Sanding- used to reduce potential of comingled remains, adhering inhibitors, and bacterial contamination

Forensic Biology by Richard Li

examples of biological evidence5
Examples of Biological Evidence
  • Teeth
    • Deciduous/Primary teeth vs. Secondary dentition/Permanent dentition
    • Dentin- Does not contain cells
    • Pulp Cavity
    • Root

Forensic Biology by Richard Li

examples of biological evidence6
Examples of Biological Evidence
  • Teeth
    • Identity of a person
      • Characteristics of teeth
      • Alignment
      • Overall structure
      • X-rays
    • Bite mark analysis

Forensic Biology by Richard Li