BIOL 3000 Genetics and Crime

Restriction Fragment Length Polymorphisms (RFLP)

Molecular technique used to identify variations in DNA sequences.

RFLP Process

Cell sample → DNA is extracted → Cleavage of DNA by restriction enzyme → Separation of DNA fragments by electrophoresis → Transfer to a membrane (Southern blatt) → Binding of radioactive DNA probe to specific DNA fragments → Membrane washed free of excess probe → X-Ray film used to detect radioactive pattern → DNA comparison

Restriction enzymes

An enzyme produced chiefly by certain bacteria, having the property of cleaving DNA molecules at or near a specific sequence of bases. Bacterial proteins such as palindromic sequences

Cleave ae specific DNA (Palindromic Sequences)

Found in prokaryotic organisms as a part of the bacterial immune system

Restriction Sites can be protected from digestion by the addition of Methyl groups

RFLP Analysis

Isolate DNA samples from crime scene and suspects → Treat DNA with Restriction Enzymes → Label DNA with radioactive markers → Electrophorese labeled DNA → Expose to X-Ray film

Variable Number Tandem Repeat (VNTR)

Any location in the genome where a short nucleotide sequence is arranged as a tandem repeat, like microsatellite repeats

Similarities of Restriction Enzymes and VNTR

Isolates DNA from a sample

Electrophorese

Number of specific cut sites in DNA yielding different band patterns

Differences of Restriction Enzymes vs. VNTR

Restriction Enzymes: Cut with enzymes, requires a lot of DNA, longer time to perform and expensive

VNTR: Specific primers to access region of interest (PCR), can use PCR to increase the DNA amount, and it is much quicker and cheaper

DNA Fingerprinting

Most often used to exclude a suspect

Victim vs. Suspects