Re: How has DNA fingerprinting helped crime solving?

Since no message was entered I will approach this question in a general manner, if you would like more detail then please feel free to post a response and I will be more then glad to clarify any questions.

As you are probably aware, DNA sequence analysis is quickly becoming a standard in forensics, or labs dealing with the investigation of criminal activity. The reason for this is the polymorphic (many forms) nature of DNA from person to person. Thus, your DNA is different then mine (linear sequence is different) so any method that can be used to characterize the DNA could potentially identify it's source (you or me...). A technique called the polymerase chain reaction (PCR) allows an investigator to amplify the amount of DNA from a given sample (say a drop of blood) without changing (usually) the sequence of that DNA.

Now, we have a larger volume of DNA from a very small amount that could have been left at a crime seen and the knowledge that the DNA sample is very unique to a given individual. Next, a variety of methods can be used to restrict (cut into smaller pieces) the DNA and run it out on a gel (called electrophoresis). "Running out on a gel" means loading the restricted DNA into a matrix (like jelly) and subjecting it to an electric field. DNA is negatively charged therefore it moves to the positive electrode. This movement depends on the size of the DNA which is determined by how is was restricted (cut up). Restriction is very dependent on composition (linear sequence). The pattern from this gel can then be analyzed and compared to others until a match is obtained.

In summary, a small amount of DNA from a crime scene can be amplified, restricted, and electrophoresed to produce a very unique sequence characteristic of the source (a person-usually).

Hope this helps.