DNA banding patterns that result from electrophoresis and the subsequent use of a specific cDNA probe during Southern Blotting, can indicate the types of VNTRs and SNPs that are present in the DNA. These DNA fingerprints may be used in a number of ways including forensic analysis, disease detection, paternity cases, and evolutionary studies.
When an individual’s DNA is cut with restriction enzymes and analyzed, differently sized restriction fragments may be produced due to mutations in restriction sites that prevent cutting. These mutations are called SNPs (Single Nucleotide Polymorphisms) and produce differently sized fragments of DNA called RFLPs (Restriction Fragment Length Polymorphisms). Since individuals contain different SNPs and produce different RFLPs, DNA may be cut with a series of different enzymes and analyzed using electrophoresis and Southern blotting. The different banding patterns that are produced may indicate the presence of specific mutations in a DNA sample. This type of DNA fingerprint analysis is used in examining DNA left at crime scenes as well as in detecting genetic diseases that are due to specific mutations.
Example:
If cells are left at a crime scene, PCR is used to amplify the DNA in the cells and the DNA fingerprint of cells left at the scene of the crime may be obtained. If the DNA fingerprint of a suspect matches the DNA fingerprint of the cells left at the crime scene, it may be used as evidence in a trial. Typically, hair follicle cells, blood cells, skin cells, and sperm cells are most commonly left at the scene of a crime.
Interestingly, each individual has two copies of each VNTR region, since there are pairs of homologous chromosomes in cells. One VNTR region is inherited from the mother and one VNTR region is inherited from the father. Due to segregation, independent assortment, and crossover that occur during meiosis, each individual inherits a unique set of VNTR regions. When a child’s DNA fingerprint (banding pattern) is analyzed, all the all bands in his/her banding pattern must correspond either to a band in the DNA fingerprint of the mother or a band in the DNA fingerprint of the father. If a child has a band that is not in the mother’s banding pattern, it must be present in the father’s banding pattern. As a result, DNA fingerprints are of value in solving paternity cases. The only individuals that have identical VNTR regions and the same DNA fingerprints are identical twins, since they arose from the same fertilized egg.
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