DNA Fingerprinting Study Notes

Definition: DNA fingerprinting, also known as DNA profiling or genetic fingerprinting, is a molecular technique used to identify individuals based on their unique DNA characteristics.
Pioneer: Alec Jeffries was the scientist who first developed the concept of DNA fingerprinting in 1984 at the University of Leicester.

Initial Work: Jeffries was examining DNA using X-rays and discovered he could differentiate between individuals based on their DNA characteristics.
Application: Within three years of its development, DNA fingerprinting became the standard for forensic and paternity testing worldwide.
Privatization: Eventually, the technique was privatized and found widespread use across various sectors.
Future of DNA Analysis: There is a suggestion that DNA fingerprinting may eventually be supplanted by complete DNA sequencing (analyzing all nucleotide sequences within the DNA).

Composition: Human DNA consists of long linear segments that are composed of genes.
Homogeneity: 99.9% of human DNA across individuals is identical; individuals share the same genes but may have different alleles (variations of those genes) that contribute to their unique physical traits.
Importance of Non-coding DNA: Previously referred to as "junk DNA," recent research recognizes it as crucial in regulating gene expression and phenotypic traits which natural selection acts upon.

Short Tandem Repeats (STRs):
- Definition: DNA sequences that consist of repeating units of 2-6 base pairs in length.
- Role: STRs are areas of high variability among individuals, making them useful for DNA profiling.
- Comparison with Other Techniques:
- VNTR (Variable Number Tandem Repeats): An earlier method that has mostly been replaced by STRs due to efficiency.
- RFLP (Restriction Fragment Length Polymorphism): Another historical technique prior to STRs.

Extraction and Preparation:
- Restriction Enzymes: Used to cut the DNA at specific sites, allowing for editing and extraction of STR regions.
- Polymerase Chain Reaction (PCR): Amplifies the extracted DNA segments, producing millions of copies.
- Gel Electrophoresis: A method for separating DNA fragments by size:
- DNA is loaded into a well in an agarose gel and subjected to an electric current.
- DNA fragments are negatively charged and migrate towards the positive electrode, separating based on size.
Visualization:
- The resulting bands on the gel represent different individuals based on their unique STR patterns.
- A profile is created by comparing the STR lengths and patterns between samples.

Use in Crime Scenes:
- In a hypothetical murder case, DNA samples from suspects (Mr. Blonde, Mrs. Red, Mr. Mustache) and the crime scene blood enable profiling.
- By comparing STR patterns, the identity of the guilty party (e.g., Mr. Blonde) can be established based solely on DNA matching.
Paternity Testing: STR analysis can also determine familial relationships, such as identifying a child's father.

Database and Privacy Concerns:
- The FBI and other organizations have created DNA databases that compile profiles from individuals.
- Concerns: Risks of genetic data misuse—insurance companies could exploit genetic predispositions gleaned from DNA results (e.g., for conditions like Alzheimer’s or breast cancer).
Limitations and Misinterpretations: DNA evidence cannot definitively prove guilt or innocence, as it does not account for contamination or wrongful framing (e.g., police mishandling evidence).

Uniqueness of DNA Profiles: The likelihood of two individuals having identical DNA fingerprints, except for identical twins, is astronomically low, making it a powerful tool for identification.
Future Trends: While DNA fingerprinting remains significant, advancements indicate a possible shift towards extensive DNA sequencing technologies.