also known as

DNA Fingerprinting

Technique:

1. Remove DNA from sample (blood, semen, live tissue, etc).

2. Use PCR to amplify the amount of DNA if needed.

3. Cut the DNA sample into smaller fragments using restriction enzymes.

4. Use gel electrophoresis to separate the fragments.

5. Transfer the DNA fragments from the gel to a filter sheet. The fragments will still be in the same positions they were after migrating along the gel.

6. Immerse the filter sheet in a bath containing radioactive probes (synthetic complementary DNA that is radioactive).

7. Expose the filter sheet to X-ray film. The radioactive probes that have become attached to the DNA fragments will expose the film and show up as dark bands, as seen in the sample at right!

1. Identifying a criminal using DNA samples from a crime scene.

2. Determining paternity, or genetic relationships between persons where that relationship is not clear.

3. Searching for the prescence of a particular gene (screening for genetic diseases).

4. Determining how closely related several similar, but different species might be.