With current technology, DNA paternity tests results have an accuracy of over Further, results are often available in less than a week. But, how exactly do these tests work and where can you get one?
Each one of us is born with a unique genetic blueprint. This genetic material is derived from the DNA of both parents. Half the DNA is inherited from the biological mother and the other half from the biological father. This is the premise on which paternity testing is built. First, samples of DNA from the child and the potential father are collected. By analyzing the results, the probability of parentage is determined. Tests for paternity identification and family relationship linking have been used for more than years.
In the early twentieth century, blood typing was the most common method. Because blood type is encoded in DNA, a child inherits one allele from each parent. For example, a person with blood type O must have two O alleles, one inherited from each parent. But it is not always this straight-forward to determine. An individual with type A blood can have either one A allele and one O allele, or two A alleles. It cannot confirm a biological relationship like fatherhood.
Instead, it can only act to exclude a potential parent based on possible blood type. With advances in DNA testing technology, paternity testing has shifted towards accurate confirmation of paternity rather than simple exclusion.
The DNA fingerprinting technology first described in has now become a powerful tool for paternity and maternity testing. It first became available for in and has since evolved. The current gold standard employs a molecular biology technique that enables exponential amplification of fragments of DNA.
This sample is typically gathered from a blood draw or by swabbing the inside of the cheek. Paternity testing based on DNA has become the most accepted method for proof of biological relationship.
Sibling DNA tests can also be performed in cases of a deceased or missing parent. These sibling tests can be used to verify if two or more individuals share a common parent. The pattern of inheritance of genetic markers between siblings are different from that between a parent and child. The DNA sample may be collected using multiple methods. The most common methods are collecting a blood sample or a swab from the inside of the cheek.
The DNA is fragmented using one of multiple approaches and the fragments are run on a gel that separates them by size creating a distinct banding pattern Figure 2. The patterns of these bands provide information about the biological relationships, as described below. There are two methods for generating DNA fragments. By looking for similar patterns in the digested fragments between the individual and the potential father, paternity is determined Figure 2.
Since each restriction enzyme has a unique sequence it recognizes, small differences in the DNA will result in cutting at different sites. By comparing the pattern of the DNA fragments cut by the restriction enzyme, paternity can be confirmed.
As far as genetic tests go, paternity tests are rather straightforward. Modern genetic testing techniques, like those used Chowdry's labs, make use of microarray testing. According to the NIH, this is a microchip-based technique which is capable of reading hundreds of pieces of genetic material at once.
This is not only capable of establishing parent-child relationships, but also of using genetic similarity to establish more distant and even ancestral familial relationships between people. While using DNA microarrays would certainly be capable of establishing paternity, according to Chowdry, these techniques would be "overkill. Given the limited variety of blood types, if all the potential fathers have the same or similar blood types, little could be inferred from the test.
While paternity tests can be performed this way, much more accurate tests have since been developed. In the s, scientists began performing the first prenatal genetic tests by gathering samples of amniotic fluid to test for chromosomal abnormalities.
Cameron is a contributing writer covering life sciences for Live Science. He holds a master's degree in animal behavior from Western Carolina University and teaches at the University of Northern Colorado. Live Science. Jump to: Choosing the right test kit Testing while pregnant How paternity tests work Paternity test history.
Cameron Duke. Finally, some people have type AB blood, which means they inherited both an A allele and a B allele. In cases of questioned paternity, ABO blood-typing can be used to exclude a man from being a child's father. For example, a man who has type AB blood could not father a child with type O blood, because he would pass on either the A or the B allele to all of his offspring.
Despite their usefulness in this regard, ABO blood groups cannot be used to confirm whether a man is indeed a child's father. Because of this and several other factors, it took the legal system some time to trust blood-typing. For example, in a famous case in , the starlet Joan Barry accused actor Charlie Chaplin of fathering her child. Although blood tests definitively excluded Chaplin as the father, the court did not allow this evidence to be admitted, and Chaplin was ordered to pay child support to Barry.
Over time, the use of additional blood antigens, such as those associated with the MN and Rh systems, refined the use of blood-typing for both paternity and forensics. The genes responsible for the HLA system are involved in antigen presentation to T cells.
The HLA system is highly polymorphic , with more than 3, different alleles identified so far Robinson et al. Although this vast number of alleles causes headaches for cell and organ transplants, the multiplicity of genotypes the HLA system provides—in the tens of millions—makes it ideal for consideration in identity and paternity testing.
In the s and s, electrophoresis of various biochemical markers became widely available. With this process, proteins from a person's blood or other tissue were placed onto a gel, such as potato starch, agarose, or polyacrylamide.
Differences in isozymes relate to differences in the alleles that code for these proteins. Thus, the presence of certain identical isozymes in samples from both a child and his or her potential father could be used to reveal the existence of a genetic relationship between the two individuals Figure 1.
In fact, by , Chakraborty et al. Today, with the advent of numerous DNA sequencing, amplification, and testing techniques, paternity testing has evolved even further than predicted. Indeed, present-day genetic testing has an accuracy rate of up to Of course, the exact level of accuracy depends on the number and quality of the genetic markers being considered. Here, it is important to emphasize that scientists consider only specific marker alleles, rather than entire genomes, when conducting paternity testing.
Full genome analysis would add a great deal of time and expense to the process without significantly improving the accuracy of the results. Thus, DNA-based forms of paternity testing have all but taken over earlier methods. In addition, higher throughput, better sensitivity, and automation have allowed DNA testing to be performed on ever-smaller and sometimes degraded DNA samples with greater speed and excellent accuracy.
Interestingly, improvements in paternity testing over the past several decades have not only led to an increase in the accuracy of test results, but also to expanded application of various testing methods. For example, as DNA technology has gotten more precise, it has become possible to determine paternity using DNA from grandparents, cousins, or even saliva left on a discarded coffee cup.
Such DNA testing is clearly an important part of criminal investigations, including forensic analysis , but it is also useful in civil courts when the paternity of a child is in question.
The widespread availability of paternity tests on the web and in neighborhood drugstores is also indicative of a civil demand for this technology.
However, it is important to note that such direct-to-consumer DTC tests will not stand up in court because there is no way to prove whose samples were analyzed. Hence, DTC testing is most often used to assist in making a decision to initiate litigation or to simply provide peace of mind in matters of questionable paternity.
In broader applications, advances in paternity testing mean that people who were adopted now have more direct means to confirm their biological identity or to find their birth parents.
In addition, parentage testing is often an essential tool in proving immigration status in cases of family reunification. For years, questions of paternity presented a significant challenge to scientists and potential parents alike. During the first half of the twentieth century, researchers often turned to people's ABO phenotypes when such issues arose; however, ABO blood group information could only be used to exclude potential fathers, rather than confirm the presence of a parental relationship.
Consideration of additional blood markers, such as Rh antigens, MN antigens, and HLAs, greatly increased the effectiveness of paternity testing over the next few decades, but it still left significant room for error. Thus, with the dawn of DNA analysis and sequencing techniques in the s and s, scientists increasingly began to look at people's genomes when questions of fatherhood arose. This approach proved exceedingly useful; in fact, current marker-based methods of analysis yield test results that are both With the ongoing advancement of DNA sequencing and analytical technologies, we will no doubt continue to see an increase in the utility of these tests, as well as in the availability of detailed genetic services to the general public.
Bhende, Y. A "new" blood group character related to the ABO system. Lancet , — Carey, L. Trends in DNA forensic analysis. Electrophoresis 23 , — Chakraborty, R. Exclusion of paternity: The current state of the art.
American Journal of Human Genetics 26 , — Jeffreys, A. Individual-specific "fingerprints" of human DNA. Nature , 76—79 doi Robinson, J.
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