Genetic fingerprinting uses variations in short tandem repeats (STRs) within non-coding regions of DNA called extrons to generate a unique DNA profile for each individual. The process involves extracting DNA from a sample, cutting it into fragments around the STRs, separating the fragments by size using electrophoresis, transferring the pattern to a membrane, and using radioactive probes to expose the membrane and produce a visible pattern of bands that serves as the individual's unique genetic fingerprint.

1. Genetic fingerprinting Each DNA profile is unique!

2. Genetic fingerprinting Regions of chromosomes that code for proteins are called introns . Other regions that are non-coding are called extrons.

3. Genetic fingerprinting Extrons contain blocks of repeated nucleotides called short tandem repeats (STRs) It is the number of times that these STRs are repeated that produces the variations in individuals.

4. Genetic fingerprinting

5. How it is done – part 1 DNA is extracted from sample. Cut into millions of small fragments Using restriction endonucleases Aimed at STRs

7. How it is done – part 2 DNA fragments are separated by electrophoresis (Fragments are exposed to electric current in a trough of gel) Different fragments move at different rates through the gel.

8. How it is done – part 2 The smaller the fragment – the faster it moves. DNA is separated into bands according to size of the fragments.

9. How it is done – part 3 The pattern of fragments are transferred to a nylon membrane by a process called Southern blotting .

10. How it is done – part 4 Radioactive probes are used to attach to specific parts of the fragments. Any probes not bound are washed off. The membrane is dried

11. How it is done - part 5 The nylon sheet is placed under X-ray film. The radioactive probes on the DNA fragments expose the film. This produces visible pattern of light and dark bands which is unique to each individual.