Strictly speaking, a paternity test is not a genetic test because it provides little information about inherited genes. Their only utility, however, is to determine the length of individual DNA segments, and in doing so reveals much about ancestry. For this, it is important to use electrophoresis, since it allows the separation of these segments, which after being analyzed, allows to derive the relevant conclusions.
In that sense, a person inherits half of his genetic load from his biological father. Real genes make up only a small part of this: 98% of genetic information consists of non-coding areas, whose function is usually unknown. Some of these sections are replete with repetitions: short sequences of DNA letters that are always aligned in the same way. Paternity testing is based on analysis of these sections of DNA. These tests require:
- Taking the sample from the parents and child.
- Sample extraction and purification.
- DNA cutting and multiplication.
- Gel electrophoresis separation.
- Statistical analysis and the conclusions of the study in probabilistic terms.
What is the usefulness of STRs in paternity testing?
Scientists designate these repetitions with Short Tandem Repeat (STR). STRs consist of two to seven DNA bases that can be repeated dozens of times. The “CATC” segment, for example, can occur ten times in one person, but twenty times in another. There are countless STRs that come together again for each person. They are as individual as a fingerprint and allow for near-unique identification of people (with the exception of identical twins).
Criminologists were among the first to develop a practical application for STR analysis. As a “genetic fingerprint” (equivalent to a fingerprint), he has already convicted many criminals. But for several years now, STR analysis has also been the method of choice for clarifying contentious paternity issues.
For a paternity test, at least two samples are needed: one from the child and one from the prospective parent, and it is better if the mother also agrees to participate in the analysis. Researchers then carefully compare genetic fingerprints and can determine whether paternity can be ruled out or is highly likely.
How is genetic paternity testing done?
The first step in a paternity test is to obtain suitable samples for DNA analysis. Since DNA samples are susceptible to contamination or degradation, it is suggested to use collection and storage devices until their final analysis. The test can even be done after a person’s death. Virtually any body tissue is suitable for this, but most of the time they are used:
- Oral mucosal smear.
- Blood samples.
- Ear plugs.
- Scraps of razor beard.
The amount of DNA extracted from these samples is usually very small; for analysis, researchers have yet to duplicate the DNA. They use polymerase chain reaction (PCR) to do this: Within a few hours, thousands and thousands of copies of STR sections can be produced. The DNA copies are then attached to a pigment to make them visible at the next stage.
How is paternity established?
STR sections differ in length, and therefore DNA copies that originate from the polymerase chain reaction are also of different lengths. Thus, scientists send the DNA copies across a flat surface (with an appropriate gel) in a closed tank, in which small copies move faster than large ones. In this very important separation process, called gel electrophoresis, the length of the DNA copies can be deduced from the rate at which they migrate.
In a paternity test, 15 to 40 DNA markers are typically tested. At the end of the laboratory analysis, scientists have a large number of measuring points, that is, separately for the father, the child and, usually, also for the mother. This alone means that little has been gained: the decisive factor is the following statistical evaluation of data with special programs.
In the end, only one thing can be established with certainty: that man is not the father of the child. The inverse conclusion, that he is indeed the father, can never be proved definitively. A paternity test can only indicate odds here, even if they are sometimes very high. Typically, the odds listed here are:
- 0%, in this case is not the parent).
- More than 99 percent, in this case it’s highly likely that he’s the father.
Kalstein electrophoresis cells
Laboratories carrying out special genomic tests may benefit from having an electrophoresis cell from the manufacturer of Kalstein instruments. These cells, which separate the bands horizontally, also have a buffer reservoir that ensures cooling and precise pH control, and the electrodes are easy to assemble and disassemble. To purchase, review prices and additional technical specifications, you can go to the link HERE