2Y Forensics Lecture 4 2022- Profiling 1 initial upload version

DNA Profiling Methodology

Lectures 4 & 5 Learning Objectives

Understand the history and applications of blood grouping in forensic analysis
List and explain immunological and protein markers for individual identification
Explain methodologies of forensic DNA analysis
Understand DNA analysis applications for human identification and wildlife
Consider ethical issues related to DNA analysis in Forensic Bioscience

Blood Grouping

Continued relevance in various countries for forensic analysis
Historical cases demonstrate efficacy
Quick, inexpensive screening eliminates large samples
Discovery of more independent blood grouping systems along with ABO:
- Protein Variants: Extend beyond just blood cell-related proteins
- Limitations: Potentially small quantity of blood available
- Diversity: Increasing typing systems reduces shared combinations among individuals

Blood Type Overview

Blood Types and Corresponding Antigens/Antibodies:
- A: Antigen A, Antibody anti-B
- B: Antigen B, Antibody anti-A
- AB: Antigen AB, No antibodies
- O: No antigens, Both anti-A and anti-B antibodies

Blood Type Distribution in the UK

Distribution and prevalence of different blood types, significant for forensic analysis

Odds Ratio for Blood Groups (UK)

O+: 1/3, O-: 1/15
A+: 1/3, A-: 1/16
B+: 1/12, B-: 1/67
AB+: 1/29, AB-: 1/167
Class ABO results from 2017-18 recorded similar ratios

Biological Markers

Immunological Markers
- Blood Group Systems: ABO, Rhesus
Protein Markers
- Important proteins associated with blood characterization:
  - AChE (Acetylcholine Esterase)
  - ACP (Acid Phosphatase)
  - Haemoglobin variants
  - PGM (Phosphoglucomutase)
  - G-6-PD (Glucose-6-phosphate dehydrogenase)

Secretor Status

Approximately 75-85% of the population are secretors
Secretors have body fluids with antigen profiles similar to their serum
Higher concentrations of A & B antigens present in secretors

History of DNA Profiling

1984: Discovery by (Sir) Alex Jeffreys, accidental discovery
First Use: Conviction of Colin Pitchfork marked the practical application of DNA profiling

Sources of DNA

Good Sources: Skin cells, urine, hair shaft
Bad Sources: Faeces less reliable in DNA recovery

Types of Markers in DNA Profiling

Autosomal STRs: Excellent for discrimination, requires quality DNA
- Examples: TPOX, D3S1358, D5S818
SNPs: Usable on degraded DNA, lower discrimination power than STRs
- Example: AMELX
Y-Chromosome Markers: Focus on male lineage, useful with mixed samples
Mitochondrial DNA: Useful in mass disaster contexts, high copy number, lower discrimination

Methodology: RFLP vs PCR for STR Analysis

RFLP (Restriction Fragment Length Polymorphism):
- Requires large quantities of undegraded DNA
PCR (Polymerase Chain Reaction):
- Suitable for small quantities, can handle partially degraded DNA

Identical Twins and DNA Analysis

Identical twins share the same DNA profile, posing unique challenges in forensic identification

Advantages and Disadvantages of DNA Profiling Methods

Autosomal STRs:
- Advantages: Small samples, high discrimination
- Disadvantages: Reduced ability with degraded DNA
Y-Chromosome STRs:
- Advantages: Useful for mixed gender samples
- Disadvantages: Low discrimination among male relatives
Mitochondrial DNA:
- Advantages: Effective with badly degraded samples
- Disadvantages: Limited discrimination in maternally related individuals

Summary of Learning Goals

Distinguish individuals by blood typing
Identify good sources of DNA
Explain the Amelogenin locus for sex identification
Recognize STR profiles with best discriminatory power

Revision Notes: Forensic DNA Analysis and Blood Grouping

Intended Learning Outcomes

Understand the history and use of blood grouping in forensic analysis
- Blood grouping has historical significance in forensic science and continues to be relevant.
- Historical cases show the efficacy of blood grouping, providing a quick and inexpensive method to screen samples.
- New independent blood grouping systems (beyond ABO) enhance the ability to distinguish between individuals.
List / explain the immunological and protein markers used to identify individuals
- Blood Group Systems: ABO, Rhesus
- Immunological Markers:
  - Antigens present in blood types (A, B, AB, O) referring to blood type specificity.
- Protein Markers:
  - AChE, ACP, Hemoglobin variants, PGM, G-6-PD
- Secretor Status:
  - 75-85% of the population are secretors, impacting the presence of antigens in body fluids.
Explain the methodologies of forensic DNA analysis
- Sources of DNA: Best sources include skin cells, urine, and hair shaft; feces are less reliable.
- Types of DNA Markers:
  - Autosomal STRs: Exceptional for discrimination, e.g. TPOX, D3S1358.
  - SNPs: Applicable for degraded DNA, but have lower discrimination abilities.
  - Y-Chromosome Markers: Useful for male lineage analysis.
  - Mitochondrial DNA: Best for mass disaster contexts but offers lower discrimination power.
- Methodological Approaches:
  - RFLP for undegraded DNA; requires larger quantities.
  - PCR for smaller or partially degraded samples.
Understand the application of DNA analysis in identification of a human individual
- Human identification relies on robust analysis of DNA, using a combination of methodologies to ensure accuracy.
- STR profiles are crucial for distinguishing individuals effectively.
Understand the uses of DNA analysis in identification of wildlife
- DNA methodologies allow for the identification of species and individual animals, aiding in conservation efforts and wildlife management.
Consider the ethical issues of DNA analysis relating to Forensic Bioscience
- Ethical considerations include privacy concerns, the potential for misuse of DNA data, and implications for wrongful convictions.
- Discussion on consent and the use of DNA databases in forensic investigations is essential.