Lecture 2: DNA Analysis

Wayne Walker

Works at Indian River Crime Lab in Ft. Pierce, FL, specializing in DNA analysis.

Forensic Biologist

Examines evidence to find biological material and develops DNA profiles from it.

Sources of Biological Evidence

Includes blood, semen, saliva, urine, hair, teeth, bone, tissue, and epithelial cells.

Limitations of DNA Testing

Factors such as temperature, sunlight, humidity, age of stain, contamination, and the material the stain is on can affect results.

Conventional Serology

A process that identifies body fluids through visual examination, presumptive testing, and confirmatory testing.

Presumptive Testing for Blood

Kastle-Meyer test, which turns pink if blood is present.

Confirmatory Testing for Blood

Hematrace test, used to confirm if blood is human.

Presumptive Testing for Semen

Acid phosphatase test, which turns red if semen is present.

Confirmatory Testing for Semen

p-30 test, which involves microscopic examination.

Presumptive Testing for Saliva

Amylase plate test, which detects alpha amylase from saliva.

DNA Structure

A double helix that makes up the genome, compressed into chromosomes.

Types of DNA Testing

Includes nuclear testing (STR & PCR based), mitochondrial testing (maternally inherited), and Y-STR testing (paternally inherited).

STRs

Short Tandem Repeats, which are 2-7 base pairs long and consist of repeated sequences.

DNA Analysis Process

Involves extraction, quantification, amplification, separation, and analysis of data.

Likelihood Ratio (LR)

A statistical measure used to evaluate the strength of DNA evidence.

Probabilistic Genotyping

Uses statistical theory and algorithms to infer genotypes and calculate likelihood ratios.

CODIS

FBI's DNA database containing profiles from convicted offenders, crime scene samples, and missing persons.

Bullet Lead Analysis

A flawed forensic method that linked bullets to suspects based on elemental makeup, later deemed unreliable.

Microscopic Hair Comparison

A method criticized for overstating match significance, leading to wrongful convictions.

Confirmation Bias

A cognitive bias that can affect forensic analysis, where examiners may favor evidence that supports their initial hypothesis.