DNA Typing and Forensics Overview

Overview of DNA Typing in Forensics

• Applications of DNA Testing:
  • Crime solving: Matching suspects with evidence.
  • Paternity testing: Determining biological relationships.
  • Missing person investigations: Identifying remains.
  • Immigration testing: Establishing relationships.
  • Disaster victims identification and military personnel identification.
• Important Concepts:
  • DNA Structure: Large molecule made of nucleotides (sugar, phosphate, base).
  • Bases: Adenine (A), Thymine (T), Cytosine (C), Guanine (G).
  • Base pairing rules: A=T, G=C.

Detailed Structure of DNA

• A nucleotide consists of:
  • Sugar: Deoxyribose.
  • Phosphate group.
  • Nitrogenous base (A, T, C, G).
• Double Helix: Strands coil around each other forming a double helix structure, stabilized by base pairs.

DNA Typing and Its Importance

• Tandem Repeats:
  • DNA regions with repeating sequences, critical for distinguishing individuals.
  • Variability among individuals at specific loci (positions in the genome).
• These repeats are crucial for creating DNA profiles used in forensic investigations.

History of DNA Fingerprinting

• Key Milestones:
  • 1985: Alec Jeffreys develops the DNA profiling technique.
  • 1986: The Pitchfork murders exonerate a falsely accused suspect and identify the real perpetrator.

Steps in Forensic DNA Analysis

1. Collection: Gathering samples from crime scenes.
2. Storage: Properly storing specimens until analysis.
3. Extraction: Isolating DNA from biological samples.
4. Quantification: Measuring the amount of DNA available.
5. PCR Amplification: Replicating small quantities of DNA.
6. STR Typing: Analyzing specific regions of DNA for variations.
7. Data Interpretation:
   • Matching DNA profiles with known references.
8. Database Storage & Searches.

Polymerase Chain Reaction (PCR)

• Technique used to amplify DNA.
• Steps:
  1. Denaturation: Heating DNA to separate strands.
  2. Primer Annealing: Adding primers to target DNA sequences.
  3. Extension: DNA polymerase adds nucleotides to replicate DNA strands.

Capillary Electrophoresis

• Method for separating DNA fragments by size using an electric current in a gel medium.
• Produces an electropherogram to visualize the results.

Interpretation of DNA Evidence

• DNA profiles must be compared:
  • Evidence from a crime scene to suspect profiles.
  • Mother’s and father’s genetic contributions for paternity tests.
• Possible Outcomes of DNA Analysis:
  • Exclusion (no match), Non-exclusion (match), and inconclusive results.

Reference Databases and Systems

• CODIS (Combined DNA Index System): Main source of DNA profiles in the U.S.
• Canadian National DNA Data Bank: Composed of two indices:
  • Convicted Offender Index
  • Crime Scene Index

Ethical and Privacy Concerns

• Potential misuse of DNA information.
• Sample retention issues after exoneration.

Witness Cases and Applications in Wildlife Forensics

• Wildlife DNA forensics apply the same principles but differ in species identification.
• Markers used in wildlife include blood, tissue, and other biological samples.

Advancements in Genetic Genealogy

• Recent cases demonstrate the power of DNA analysis in solving cold cases through advanced genetic testing.