Core Biology Students Gel Electrophoresis (DNA analysis)

          Of the three billion nucleotides in human DNA, more than 99% are identical among individuals. The remaining 1%, however, adds up to a significant amount of code variations between individuals, making each person's DNA profile as unique as a fingerprint. Due to the large number of possible variations, no two people (with the exception of identical twins) have the same DNA sequence.

          For every 1,000 nucleotides inherited, there is one site of variation, or polymorphism. DNA polymorphisms change the length of the DNA fragments produced by the digestion of restriction enzymes, so the exact number and size of fragments produced by a specific restriction enzyme digestion varies from person to person. The resulting fragments, called Restriction Fragment Length Polymorphisms (RFLPs), can be separated, and their size determined, by electrophoresis.

          Most of the DNA in a chromosome is not used for the genetic code; it is uncertain what, if any, use this DNA may have. Because these regions are not essential to an organism's development, it is more likely that changes will be found in these nonessential regions. The regions that contain nucleotide sequences that repeat from 20 to 100 times (e.g., GTCAGTCAGTCAGTCA) are the strands cut by restriction enzymes to create RFLPs.

          The difference in the fragments can be quantified to create a "DNA fingerprint". Distinct RFLP patterns can be used to trace the inheritance of chromosomal regions with genetic disorders or to identify the origin of a blood sample in a criminal investigation. Scientists have identified more than 3,000 RFLPs in the human genetic code, many of which are highly variable among individuals. It is this large number of variable yet identifiable factors that allows scientists to identify individuals by the number and size of their various RFLPs.

          This technique is being used more and more frequently in legal matters. Using DNA fingerprinting, the identity of a person who has committed a violent crime can be determined from minute quantities of DNA left at the scene of the crime in the form of blood, semen, hair, or saliva. The DNA fingerprint matched to a suspect can be accurate to within one in 10 billion people, which is almost twice the total population in the world. Certain limitations in the technique prevent two samples from being identified as a "perfect match", yet it is possible to measure the statistical probability of two samples coming from the same individual based on the number of known RFLPs that exist in a given population.

          DNA fingerprinting has many other applications, since half of a person's genome comes from each parent, DNA fingerprinting can be used to determine familial relationships. It has a much higher certainty than a blood test when used to determine fatherhood in a paternity suit. DNA fingerprinting can be used to track hereditary diseases passed down family lines, as well as to find the closest possible matches for organ transplants. It can also be used to ascertain the level of inbreeding of endangered animals, aiding in the development of breeding programs to increase animals' genetic health and diversity.

Students use micropipettes to load their samples into agar rose gels

The gels are placed in the electrophoresis apparatus and submerged in a buffer. Once this is done the micropipette is used to load the wells in the gel