Overview
This lecture covers DNA profiling, explaining how it is created, its uses, and how to interpret DNA profiles in exams, especially for paternity and crime scene analysis.
DNA Profiling Basics
- DNA profiling analyzes unique sections of an individual's DNA to identify people.
- The correct term for the process is "DNA profiling," not "DNA fingerprinting."
- DNA profiles are used in crime investigations, paternity tests, genetic disorder identification, and human remains identification.
Creating a DNA Profile
- The process is called gel electrophoresis.
- DNA is extracted from white blood cells in a blood sample.
- Restriction enzymes cut the DNA into fragments containing short tandem repeats (STRs).
- The DNA fragments are loaded onto a gel and separated by size with an electric current.
- Large DNA fragments stay near the top; smaller ones move further down the gel.
- A radioactive probe makes the DNA markers (bands) visible for analysis.
- The visible bands are called genetic markers or simply bands.
Interpreting DNA Profiles in Exams
Paternity Testing
- Compare the child's bands to both the mother and potential fathers using a ruler or highlighter.
- The child's genetic markers should match 50% with the mother and 50% with the father.
- The father is identified as the one whose DNA markers match the remaining bands not present in the mother.
Crime Scene Investigation
- Compare the DNA bands from the crime scene to those of suspects.
- The suspect whose DNA profile has 100% matching markers with the crime scene sample is identified as the source.
- Shared markers across all samples may occur, but only a complete match is valid.
Key Terms & Definitions
- DNA Profiling — Technique to identify individuals by analyzing unique DNA sections.
- Short Tandem Repeats (STRs) — Unique, repeating DNA sequences used to distinguish individuals.
- Gel Electrophoresis — Laboratory method to separate DNA fragments by size using an electric field.
- Restriction Enzymes — Proteins that cut DNA at specific sequences.
- Genetic Marker/Band — Visible segment on a DNA profile representing a fragment of DNA.
Action Items / Next Steps
- Practice reading DNA profiles for paternity and crime scene scenarios.
- Learn terminology: DNA profiling, STRs, gel electrophoresis, restriction enzyme, and genetic marker.
- Review the structure of DNA if needed.