DNA Fingerprinting Paternity Test
Electrophoresis and Restriction Fragment Analysis
Genetic technology is used to investigate paternity. By employing an electrical current to separate DNA fragments, the genetic similarity of individuals can be assessed.
One of a Kind DNA
Everyone, except identical twins, has a one-of-a-kind DNA genome. The DNA molecule is made of monomers called nucleotides, and the specific order in which nucleotides occur in a DNA molecule represents each individual’s unique genetic code.
How Is DNA Used to Establish Paternity?
How Are DNA Samples Obtained?
DNA samples can be easily and noninvasively collected by gently rubbing a cotton swab on the inside of the check. Cells of the mucous membrane adhere to the swab, and every somatic cell a person’s body contains a complete genetic blueprint.
Comparison of Restriction Fragment Length Polymorphisms (RFLPs)
DNA restriction fragment analysis, or DNA fingerprinting, uses special proteins called restriction enzymes to cut up DNA. A specific restriction enzyme will only cut the DNA when it encounters a certain combination of nucleotides.
There are many different types of restriction enzymes, and each makes its cut at a very specific location on the DNA molecule, depending on the nucleotide sequence that it recognizes. This results in lengths of DNA, called restriction fragment length polymorphisms. For each individual, the size of these fragments is unique, like the person's DNA.
RFLPs and Electrophoresis
When DNA samples are taken from a baby, mother and possible father, each is shipped to a lab and exposed to a variety of restriction enzymes. Once the DNA is cut up, each individual’s RFLPs are placed in small wells within a gel matrix that looks much like a rectangular slab of Jell-o.
This Jell-o-like slab containing the DNA is placed in an electrophoresis chamber which contains liquid and positive and negative electrodes. Current is then run through the chamber.
DNA is negatively charged (-), and therefore attracted to anything that is positively charged (+). When current is run through the chamber, the DNA begins to migrate towards the positive pole. Large fragments will move through the gel more slowly than smaller fragments, and, after a short period of time, the RFLPs separate based on their size.
Ultimately bands of DNA are visible in “lanes” that have moved straight out of each well. Each band in a lane represents many DNA fragments that are similar in size. Since the DNA from different individuals will have been cut at different places by the restriction enzymes, each person's DNA will form a unique pattern after being run through the gel.
Comparison of DNA Fingerprints
The electrophoresed DNA pattern of child, mother and possible father are then compared. The mother and child’s pattern will show similarities, since half of the child’s genetic material is the same as the mother's. If the man being tested for a paternity is the biological father, half of his bands will match the remaining bands within the child’s DNA fingerprint.
Additional Resources
For more information on genetcs, DNA and paternity testing, see the science education website Science Prof Online or the Suite101 articles, Nucleotides & Nucleic Acids, Genetics of DNA Paternity Testing and DNA Paternity Testing - RFLPs. General information on paternity testing was obtained from The Tech - Paternity Testing & DNA Fingerprinting.
