DNA profile analysis is based on the use of the “Southern” hybridization technique to analyze the polymorphic regions of human DNA, which are the regions which have excludive genes that are unique in every human being.

Sources of DNA found at a crime scene:•Blood•Semen•Tissue from a dead victim•Hair (cells in the hair follicle)•Saliva

The DNA extracted from the crime scenes is compared to DNA (normally taken from blood) from know individuals like the victim or the suspect.

1. DNA EXTRACTION

DNA is treated with a restriction endonuclease which is an enzyme that cuts DNA whenever a specific DNA sequence (of the polymorphic region) occurs. The most commonly used is HaeIII which cuts the sequence 5’-GGCC-3’.

2. Digestion of DNA

This is used to separate DNA fragments by size, and it works like this: The DNA fragments are submerged in the agerose gel. The DNA strands tend to go to the positively charged part of the recipient. As the fragments move, they are allowed down by the matrix of the gel. Smaller fragments move more rapidly through the pores of the gel, which means the would move themselves the farthest from the origin.

3. Agarose gel electrophoresis

DNAs are denatured (the helix of DNA are unzipped) while still in the agarose gel by submerging it in a basic solution. Single strand DNA molecules are transferred to the surface of a nylon membrane, like making a tracing on a paper.

4. Preparation of a "Southern blot"

A single locus probe is a DNA or RNA sequence that is able to hybridize.The DNA strands form duplex formations by paring themselves with this probe sequences.These hybrids are incubated in a radioactive solution.After they finally join, the nylon is cleaned so the unbound probe is washed away, so that the only radioactivity remaining in the membrane is associated with the target DNA.

5. Hybridization with radioactive probe

6. Detection of RFLPs via autoradiographyThe washed nylon is placed next to a sheet of X-ray film in a light container. The X-Ray film records the locations of radioactive decay. Results can be compared now.

7. Re-probe southern blot with additional probes