Forensic DNA Analysis

Key Reminders for Lectures

• A reminder to students: Feel free to leave if anything discussed makes you uncomfortable.

Overview of DNA Techniques

• Restriction Enzymes

  • Cuts DNA at specific sites

  • Requires a lot of DNA for analysis

• Variable Number Tandem Repeats (VNTRs)

  • Larger regions in DNA, typically 10 to 100 base repeats

  • Provides information on sizes of DNA regions

  • Requires PCR for amplification

• Short Tandem Repeats (STRs)

  • Smaller than VNTRs, usually 2 to 6 base pairs

  • PCR is used to analyze these short regions efficiently

  • STRs can be differentiated easily by analyzing band sizes on a gel

  • Smaller size runs further in an electrophoretic gel

Comparing DNA Techniques

• VNTRs are often referred to as mini-satellites, larger than STRs and found in heterochromatin.

• STRs, or microsatellites, are more accessible in euchromatin, making them easier to manipulate and analyze.

Amplification and Analysis

• Design primers for STR regions to amplify using PCR.

• STRs allow for individual differentiation based on the number of repeats present.

  • Heterozygous samples show two peaks (different repeat numbers), while homozygous samples show one peak (same repeat number).

CODIS & DNA Database

• CODIS (Combined DNA Index System) founded after the 1994 DNA Identification Act.

  • Stores DNA profiles from crime scenes and convicted offenders.

• Initially based on 13 loci for profiling with recent updates adding more.

  • Local, state, and national databases work in conjunction for effective law enforcement.

Loci in CODIS

• Loci refer to specific locations on chromosomes where DNA samples are analyzed.

• The profiles from these loci allow differentiation among individuals.

Gender Identification using DNA

• Through the Amylogenin gene on X and Y chromosomes, sex can be determined.

  • One peak indicates female (XX) and two peaks indicate male (XY).

Partial Matches in DNA

• Investigations can yield partial matches, implying familial relationships.

• Significant in cases where direct connections to suspects are ambiguous (e.g., BTK killer case).

Use of Mitochondrial DNA

• Mitochondrial DNA (inherited maternally) and Y-chromosomes (inherited paternally) can aid in narrowing a suspects' pool in investigations.

Genealogy and Modern Technologies

• Companies like 23andMe and Ancestry.com have opened new methods for genetic analysis and familial matching.

• They can provide leads in cold cases, exemplified by the resolution of the Golden State Killer's case through genealogical research and comparison to DNA databases.

DNA Phenotyping

• An emerging field using SNPs (Single Nucleotide Polymorphisms) to predict physical traits from DNA.

  • Marks the difference at specific locations in the genome.

  • Can determine characteristics like hair, eye color, and even approximate age from genetic information.

Conclusion

• The lecture provides a robust overview of DNA techniques, their applications in forensics, and the evolution of DNA technology over the years. Keep these concepts in mind as they form the basis of forensic genetic analysis and identification processes.