The use of Genetic Codes

Genetic fingerprint,
Suggested Reading :

(1)	Advanced-level Biology for Hong Kong , Book 2, by Y.K.Ho, Manhattan Press, pp.247-249
(2)	Understanding Biology for Advanced Level, 4th Ed. by Glenn and Susan Toole, Stanley Thornes, pp.128-129
(3)	Biology : Principles and Processes,by Roberts, Reiss and Monger, Nelson Press, pp. 795
(4)	Advanced Biology, Principles & applications, International Student Edition, by C.J.Clegg with D.G.Mackean, John Murray, pp.646

Theoretically, except identical twins, no two people have the same genetic materials. So, genetic material can be used for identification.

When we want to compare the genetic materials between two specimen, we need to apply some DNA endonucleases enzyme to cut the DNA threads into segments. Specific endonuclease would cut the DNA thread between two specific nitrogen-bases. If the endonucleases are applied in a specific sequence, DNA would be cut into a specific number of segments, and each segment would have specific molecular mass (specific length). If two DNA specimens are the same, after the treatment, the same numbers of segments and the same molecular masses of the corresponding segments can be formed. If the two DNA specimens are not the same, then, the two specimen would yield different numbers of DNA segments, and the segments would have different molecular masses. If we want to compare the number of the segments and masses of the segments between the two specimen, we can use electrophoresis to separate the segments of the specimens. In the electrophoresis media, different DNA segments of different molecular masses and different electric charges would move over different distance. By the application of florescent material, DNA segments can be seen. Then, we can know whether there are corresponding identical DNA segements by their locations. This layerout of DNA segments is called the genetic fingerprinting.

Most forensic DNA tests check for the repetition of short sequences, called short tandem repeats (STR), within 13 areas of the genome likely to differ among individuals. Each person has two possible forms, or alleles, one from each parent. A crime sample is run against the Federal Bureau of Investigation's (FBI) DNA database to check for matches in the STR pattern at these highly variable locations, or loci. In a "hit", both alleles at all 13 loci look the same.
Sometimes the crime lab must work with as few as 10 loci because of problems with the evidence. To obtain familial or "partial match" information from the national database, investigators must find at least one allele match at each locus. Massachusetts and New York State allow labs to use just four loci for familial and some other searches, potentially implicating far more people.
(Adopted from : Scientific American, December 2006, pp.9)

In general, there are two usage of genetic fingerprinting.

(1) Forensic study
Suggested Reading,

(1)	Advanced-level Biology for Hong Kong , Book 2, by Y.K.Ho, Manhattan Press, pp.249-250

In crime sites, if the specimen (living tissue) of the murderer is collected, police can compare the genetic fingerprinting between the suspect and the specimen. If the genetic fingerprinting matches, that means the suspect is the murderer. This has been widely accepted by courts.

(2) parentage test
Suggested Reading,

(1)	Advanced-level Biology for Hong Kong , Book 2, by Y.K.Ho, Manhattan Press, pp.250

A person would get a half genetic material from the father and another half from the mother. So, the genetic fingerprinting of a person would have a half matched with the father and another half matched with the mother. By this way, if the genetic fingerprintings of the three people are compared, the parentage relationship can be proved.

(11.02.2007)