HOW IS IT DONE?
There are over 3 billion nucleotides in an individual's entire DNA sequence. Each person has about 99.9% of the same DNA sequence but the remaining 0.1% makes everyone unique, with the exception of identical twins. The greatest difference in DNA among people, or the 0.1% difference, is found in a specific region of the genome that isn't part of the genes. So, DNA fingerprinting focuses on noncoding regions of the DNA which includes repeating stretches of nucleotides. The cell used to get a DNA fingerprint could be a skin cell, hair root cell, or even a cheek cell because your DNA is the same in all of your cells. The number of repeating nucleotides in your DNA may vary with each person so to find the regions of DNA that can be identified with DNA fingerprinting, the DNA is cut with a restriction enzyme. Gel electrophoresis separates the DNA fragments created. The more repeats there are, the larger the fragment will be. The pattern of the DNA fragments once placed in the gel show the uniqueness of a person's DNA. The DNA fingerprints can then be compared to solve crime related, identification, paternity, etc. cases. If the fragments are the same size, with the same pattern, it can be concluded that the samples came from the same source. Computers are also used to calculate the probability that a match could have occurred by coincidence. The calculation can be complicated but for the majority of the time the chances are several billion to 1 making DNA fingerprinting a reliable test. On top of that, scientists will typically compare at least five regions of genome making sure that the finding was correct which makes the test just that more reliable.
SOLVING CRIMES
DNA fingerprinting can be used to solve criminal cases by comparing the DNA sample that is found at a crime scene and a suspect's DNA. Scientists know the biological evidence found at the scene came from the suspect if after close examination, the DNA profiles or fragment patterns match. On the other hand, if the profiles do not match, then they know the evidence did not come from the suspect. The Innocence Project at Benjamin Cardozo Law School in New York was able to free more than 170 wrongfully convicted people using DNA fingerprinting. However, proving the innocence of a person is easier than proving a person's guilt as things such as the possibility of a DNA sample being contaminated if not handled correctly must be taken into account.
SOLVING PATERNITY CASES
Everyone gets half their DNA from their father and half from their mother. When trying to solve a paternity case, DNA fingerprinting can come in handy. Scientists can compare the genetic fingerprints between the alleged parents and children to determine paternity. Look at the picture on the right. The 'M ' column is the mother's DNA fingerprints, the 'C' column is the child's, and the 'AF' column is the alleged father's. When trying to determine if the alleged parent, in this case the father, is truly the parent, every band in the child's fingerprint that does not match the mother's fingerprint must match in the father's. Here we see that this is the case. Every band this child does not share with it's mother, it shares with it's father. This strategy is used often and through this DNA fingerprinting, thousands of paternity causes are settled.