What is DNA profiling or DNA fingerprinting? 20分

What is DNA profiling?

To understand DNA profiling, you first have to know that large portions of any single person's DNA are the same as every other person's. But other sections - or fragments - of human DNA are unique to the individual. These fragments are called polymorphic because they vary in shape from person to person. Essentially, DNA profiling is the process of separating an individual's unique, polymorphic, fragments from the common ones.

Restriction fragment length polymorphism (RFLP) is the process used to identify Colin Pitchfork. This approach to DNA profiling can pretty much be summed up, "extract it, chop it, sort it, photograph it." RFLP requires a relatively large sample of DNA - twenty-five or more hairs or a nickel-sized blood or semen stain - and the fresher the better.

Once the DNA's been extracted, it's mixed with a chemical called a restriction enzyme. Essentially, the restriction enzyme cuts the DNA into fragments (the so-called restriction fragments) at specific points in the DNA sequence.

The next step is to sort the fragments, using a technique called electrophoresis. The shorter fragments move farther and faster than the longer ones, so once the current's been shut off, the fragments have lined up according to length.

So now you've got the actual DNA pattern - it's strewn along the block of gel. While all of the DNA contained in the sample has been transferred from the gel to the blot, the probe DNA is designed to attach itself to the polymorphic - and only the polymorphic - fragments. All other DNA is washed off, leaving just the unique fragments. The probe material is radioactive, so when a piece of X-ray film is pressed against the blot, a photo called an autoradiograph or autorad (meaning "self-radiating") is created, containing the familiar "bar code" pattern of a DNA "fingerprint."

2008-10-20 09:50:05 補充：
Are there other types of DNA profiling?

One new development is testing for short tandem repeats (STRs)r, a PCR-based allele-specific test that can get results from samples that were previously too damaged to be usable.

2008-10-20 09:50:57 補充：
The most prevalent method of DNA profiling used today is based on PCR and uses short tandem repeats (STR). This method uses highly polymorphic regions that have short repeated sequences of DNA

2008-10-20 09:51:01 補充：
(the most common is 4 bases repeated, but there are other lengths in use, including 3 and 5 bases). Because different unrelated people have different numbers of repeat units, these regions of DNA can be used to discriminate between unrelated individuals.

2008-10-20 09:51:50 補充：
Pls find more details here:

http://en.wikipedia.org/wiki/DNA_profiling
http://www.kathyreichs.com/dnaprofiling.htm