Technique of DNA profiling

DNA profiling can be done using a number of different techniques; the commonest one is based on STR. The steps are:

1: Extract and purify DNA.

• DNA is extracted from any nucleated cells then purified from the remains of the proteins and other cellular material.

2: Target and Amplify

• Use PCR to copy particular areas of DNA called short tandem repeats (STR)

3: Tagging.

• Fluorescent tags are added to each sample to help with profiling in latter steps.

4: Sizing and sorting.

• The DNA pieces are sorted according to size by a sieving technique called electrophoresis. The DNA is poured into a gel, such as agarose. An electrical charge is applied to the gel, with the positive charge at the bottom and the negative charge at the top. Because DNA has a slightly negative charge, the entire DNA will be attracted towards the bottom of the gel. However, the smaller pieces will be able to move more quickly and thus farther towards the bottom than the larger pieces. The different-sized pieces of DNA will therefore be separated by size, with the smaller pieces towards the bottom and the larger pieces towards the top.

5: DNA profile.

• The final DNA profile is built by using several STR loci (5-10 or more) simultaneously. As the DNA moves through the gel, a laser excite the fluorescent tags and a picture is made of the pattern of bands representing the lengths of the STR is built up.

Category: Forensic Medicine Notes