PCR Question... please help!

[chrispa]

I was working on finishing my lab on DNA when I came across this question:

The forensic PCR that is used by the RCMP and FBI in crime scene investigation actually
looks at the DNA profile of an individual at 13 different loci. Explain the logic behind looking at more than one
locus before you would proceed to arrest and subsequently convict a suspect. Describe in detail the changes in
your level of confidence as you increase the number of loci that are examined for an individual’s DNA
“fingerprint”. Please use the three following scenarios as the framework for preparation of your answer: 1 locus
versus 2 loci; 2 loci versus 3 loci; and 12 loci versus 13 loci.

Just wondering if anyone could offer some help. I dislike seeking others assistance on lab work, but this question really threw me off and it is worth a decent amount of points. Thanks a lot, any help is much appreciated!

[JackBean]

Well, if that are microsatellites (MS; as probably they are), you are looking for length of them. But still, there will be plenty of people with the same number of MS (how many of 6 billion people will have one of let's say 50 possibillities?), the simplest example is your own lineage. If you look for two loci, you will cut down the possibillity to half and so on...

On the other hand, you are not examining all the people on the world, of course So, you must find some reasonable compromise in between how many loci you will examine (that is how much it will cost per examined person) and your accuracy