1. Structure and Function within Forensic Science
DNA
Structure and Function within Forensic Science

2. DNA Structure Deoxyribonucleic acid
DNA provides the instructions for all proteins
DNA is the blue-print for your phenotype. The DNA cannot be used directly to make proteins it must be re-formatted as such: DNA  mRNA  Proteins

3. DNA Structure Nucleotides are the building blocks of DNA
Sugar- Deoxyribose
Phosphate group
Nitrogenous Base-
Adenine
Guanine
Cytosine
Thymine

4. DNA Structure
Sugar and Phosphate bond to form the backbone of DNA

5. DNA Structure Pyrimidines Purines Pairing Thymine Cytosine Adenine
Guanine
Pairing
A—T
G—C

6. DNA Structure DNA is shaped in a double helix
The double helix is formed by the two strands being antiparallel
Antiparallel: Each DNA strand runs side-by-side, but in opposite directions
5’ to 3’
3’ to 5’
The two strands are held together by hydrogen bonds between the nitrogenous bases

7. DNA Use in Forensic Cases
Most are rape cases (>2 out of 3)
Looking for match between evidence and suspect
Must compare victim’s DNA profile
Mixtures must be resolved
DNA is often degraded
Inhibitors to PCR are often present

8. Human Identity Testing
Forensic cases -- matching suspect with evidence
Paternity testing -- identifying father
Historical investigations
Missing persons investigations
Mass disasters -- putting pieces back together
Military DNA “dog tag”
Convicted felon DNA databases

9. Sources of Biological Evidence
Blood
• Semen
• Saliva
• Urine
• Hair
• Teeth
• Bone
• Tissue

10. DNA Collection & Comparison
Analysis of DNA??
Uses various DNA Technologies
RFLP
PCR
STR
Mitochondrial DNA Analysis

11. RFLP: Restriction Fragment Length Polymorphism
Analyzes variable lengths of DNA fragments by cutting them out using a restriction enzyme
Forensic scientist take out a sequence of 15 to 35 bases and analyze repeats throughout DNA helix
The repeats are found using an engineered complimentary sequence (man-made replication)
One of the original applications of DNA analysis. Not used as much anymore because it requires a large quantity of DNA sample and samples degraded by the environment do not work well with RFLP

12. PCR: Polymerase Chain Reaction
Replaced RFLPs test
Used to make millions of exact copies of DNA from a biological sample
DNA polymerase is used to synthesize a region of DNA
Steps:
Heat DNA
Cool DNA and add primers
Reheat and add DNA polymerase which rebuilds the double stranded DNA
Repeat these steps times to engineer a much larger and complete DNA strand
Must be very careful about contamination in this process

13. STR: Short Tandem Repeat
Most successful and widely used today
Evaluates specific regions (loci) within nuclear DNA
Looks at the repeating letters found in our DNA (GAT GAT GAT) which are useful as markers throughout the DNA
Very useful when dealing with DNA that has undergone degradation
FBI uses 13 standard specific STR regions for CODIS

14. Mitochondrial DNA Analysis
Used for samples that cannot be analyzed using RFLP or STR
Uses DNA extracted from mitochondrion rather than nuclear DNA
Especially useful in old cases and old samples