The science behind DNA Paternity testing

The science behind DNA Paternity testing

Eminent scientist Dr Ron Ostrowski lays out here exactly how it is that the paternity of a child can be proved or disproved using DNA analysis;

“DNA (alleles) from the mother, child, and alleged father are extracted, amplified, and identified. A series of mathematical calculations are then used to either completely exonerate an accused man or provide an estimate of probability of his paternity (POP).
Genetic Markers
Half of a child’s genetic material (alleles) come from the mother, while the other half is contributed by the father. A series of genetic systems (loci) are analyzed in an attempt to ascertain the biological father of a child. Each genetic system in a person has two allele, these alleles are numerically labeled. In paternity testing, the alleles from the child are compared to those of the “parents” to determine if it is possible for either or both parents to have contributed the particular alleles present in the child. For instance, assume that a child has a 10 and 11 allele for a particular genetic system and the child’s mother is known to possess a 10 and a 12 allele for this system. The mother must have contributed the 10 allele and the 11 allele must be paternal. In this example, any man who does not possess an 11 allele could not be the child’s father (barring the possibility of mutation that converts one allele to another – something that is unlikely but can be taken into consideration if needed). In the event that a man is not excluded, the likelihood that a randomly chosen man might also be able to provide the allele in question to the child can be determined by examining the allelic frequencies from a relevant population database.
Paternity Index
The paternity index (PI) compares the likelihood that a genetic marker (allele) that the alleged father (AF) passed to the child to the probability that a randomly selected unrelated man of similar ethnic background could pass the allele to the child. This is presented in the formula X/Y, where X is the chance that the AF could transmit the obligate allele and Y is the chance that some other man of the same race could have transmitted the allele. X is assigned the value of 1 if the AF is homozygous for the allele of interest and 0.5 if the AF is heterozygous. The potential of a randomly selected man to pass the obligate gene is determined by using a database which lists the frequency distribution of individual alleles within a given genetic system.
Combined Paternity Index
The combined paternity index (CPI) is determined by multiplying the individual PIs for each locus tested. The CPI is an odds ratio that indicates how many times more likely it is that the alleged father is the biological father than a randomly selected unrelated man of similar ethnic background. The CPI is based solely on genetic evidence.
Probability of Paternity
To convert the genetic evidence to a probability of paternity (POP) it is necessary to use the Baysian theorem. This is a formula that tests the hypothesis that the accused is the biological father of the child. For example, a POP of 99% reflects a 99% probability that the hypothesis is correct and a 1% probability that it is not. The CPI is used in the Bayes formula along with another variable called a prior probability (PP). This variable represents the social evidence. Testing labs typically use a value of 0.5 for the PP assuming this is a neutral, unbiased value. The Baysian formula is CPI / CPI + (1 – PP) x 100.

Visit www.dna-genie.com for a full range of paternity tests including sibling dna tests to determine paternity.


Popularity of paternity DNA testing

With the growing popularity of paternity DNA testing in society today there is some confusion as to how accurate the tests can be. Below is the Wikipedia explanation for clarification


“Parental testing is the use of genetic fingerprinting to determine whether two individuals have a biological parent–child relationship. A paternity test establishes genetic proof whether a man is the biological father of an individual, and a maternity test establishes whether a woman is the biological mother of an individual. Though genetic testing is the most reliable standard, older methods also exist, including ABO blood group typing, analysis of various other proteins and enzymes, or using human leukocyte antigen antigens. The current techniques for paternal testing are using polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP). Paternity testing can now also be performed while the woman is still pregnant from a blood draw.[1][2] DNA testing is currently the most advanced and accurate technology to determine parentage. In a DNA parentage test, the result (called the ‘probability of parentage)[3] is 0% when the alleged parent is not biologically related to the child and the probability of parentage is typically 99.99% when the alleged parent is biologically related to the child. However, while almost all individuals have a single and distinct set of genes, rare individuals, known as “chimeras“, have at least two different sets of genes, which can result in a false negative result if their reproductive tissue has a different genetic makeup from the tissue sampled for the test”

Given this information the importance of employing a fully accredited lab if you are thinking of doing a paternity test is key. DNA Genie in Harlow Essex are one very highly regarded lab. Visit their website here;


Some more here about the legalities of paternity testing

“In the United Kingdom, there were no restrictions on paternity tests until the Human Tissue Act 2004 came into force in September 2006. Section 45 states that it is an offence to possess without appropriate consent any human bodily material with the intent of analyzing its DNA. Legally declared fathers have access to paternity testing services under the new regulations, provided the putative parental DNA being tested is their own. Tests are sometimes ordered by courts when proof of paternity is required. In the UK, the Ministry of Justice accredits bodies that can conduct this testing. The Department of Health produced a voluntary code of practice on genetic paternity testing in 2001. This document is currently under review, and responsibility for it has been transferred to the Human Tissue Authority.”

DNA Paternity testing common misconceptions

DNA Paternity testing common misconceptions

With the proliferation of cheap DNA test kits available at drugstores and companies advertising quick and easy paternity tests, it is easy to become confused about what is fact and what is fiction when it comes to DNA testing. The commercialization of the industry may also have added to the confusion, and making an informed choice has become difficult. Identifying the myths and learning the facts about DNA testing can help you to choose a qualified laboratory to perform the tests at an affordable price.

DNA Testing Is Expensive

Because of the recent advances in genetic testing and technology, DNA testing facilities have been able to provide more accurate results and charge less money. It is still important to check the credentials of any laboratory or company that advertises extremely low prices to make sure they are accredited and aboveboard. Some DNA tests may be done for as little as $100, with many averaging between $400 and $600.

Any DNA Test May Be Used in Court

Only a laboratory accredited by the AABB may do a DNA test that produces results that may be admissible in court. DNA testing facilities like gtldna.com understand the careful process that the courts require in order to prevent the samples from potential tampering. The legal requirements include proper identification of all parties involved in the test and collection by a professional with no relation to any of those tested or any bias toward the outcome of the test. These results may be used for cases involving child support or custody, inheritance, welfare benefits, adoption, or immigration.

DNA Testing Requires a Blood Sample

Although DNA testing used to involve having a sample of blood drawn, the tests now are much simpler and no blood work or needles are required. A swab of cotton on a stick is swiped against the inside of the cheek to collect a saliva sample which is then analyzed by the laboratory. This is called a buccal swab, and the sample is easy to collect even with an infant. Until fairly recently, prenatal samples were invasive and could even cause miscarriages; however, there is now a non-invasive way to collect a sample on an unborn child.

DNA Testing Destroys Families

In any situation where parentage is in doubt, there can be emotional distress upon learning the truth. This can especially be true in paternity cases, or in family-based petitions for immigration where an attempt to provide relationship evidence reveals family secrets and prevents the immigration. Although these sensational concerns get the most attention from the media, DNA testing is more commonly used to verify paternity for child support and inheritance cases or for genealogy purposes.

The Father Must Participate to Establish Paternity

If the potential father refuses to cooperate and take a paternity test, or if he is deceased, the DNA test can be taken by the parents or brother of the father and compared to that of the child to determine if there is a biological relation.

Whether you are considering DNA testing to establish paternity for child support or trying to get a more accurate idea of what countries your ancestors came from, finding a cheap DNA test from a qualified laboratory does not have to be confusing. By checking into the testing facility’s accreditations and certifications and reading reviews about them online you can determine quality and compare these against others to find the lowest prices and make your selection.

Types of blood and DNA for Paternity Test

Types of blood and DNA for Paternity Test

Paternity Testing: Blood Types and DNA

The modern-day paternity test compares a baby’s DNA profile to the potential father’s. How did we ever manage it before genetics?

Occasionally, situations in DNA paternity test arise in which people require concrete, scientific evidence of parentage, whether it be their own or that of someone else. In most instances, maternity is easy to determine. Before surrogate motherhood became possible, the woman who gave birth to a child was obviously that child’s gestational, genetic, and legal mother, and this continues to be true in the vast majority of cases today.

Unfortunately, questions of paternity aren’t so easy to answer. In order to make a determination of fatherhood, scientists almost always work backwards–from the child to the potential parent–to ascertain the actual nature of the relationship. In the past, this typically involved identifying specific phenotypes (in particular, specific blood types) in the child and using this information to either “rule in” or “rule out” possible fathers. However, this system presented a number of problems, not the least of which was that it often yielded inconclusive results. Thus, since the 1990s, the more common approach has been to consider the presence of particular genotypic markers when attempting to establish fatherhood (and, in a handful of cases, motherhood).

Using Blood-Typing in Paternity Tests
The process of DNA fingerprinting was developed by Alec Jeffreys in 1984, and it first became available for paternity testing in 1988. Before this sort of DNA analysis was available, blood types were the most common factor considered in human paternity testing. Blood groups are a popular example of Mendelian genetics at work. After all, there are numerous human blood groups with multiple alleles, and these alleles exhibit a range of dominance patterns.

Today, the best-known blood-typing system is ABO typing, which involves the presence of antigens on red blood cells that are encoded by the ABO locus on human chromosome 9. In the ABO system, the A allele and the B allele are codominant, and the O allele is recessive. Thus, if a person’s ABO blood type is O, he or she has two O alleles. If, however, a person’s blood type is A, he or she has either two A alleles or one A allele and one O allele. Similarly, if a person has type B blood, this indicates the presence of either two B alleles or one B allele and one O allele. 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 1943, 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. The Barry/Chaplin case did spur the passage of new laws, however, thus launching a new era in forensic evidence.

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. However, such blood groups were only about 40% effective in ruling out a man as a child’s father. Then, in the 1970s, testing for human leukocyte antigens (HLAs) added a distinguishing feature that made it possible to rule out men as fathers with 80% effectiveness. The genes responsible for the HLA system are involved in antigen presentation to T cells. The HLA system is highly polymorphic, with more than 3,200 different alleles identified so far (Robinson et al., 2003; Williams, 2001). 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.

DNA Markers and Electrophoresis

In the 1970s and 1980s, 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. An electric current was then run through the gel, and different forms or isozymes of the proteins were separated by their electrical charge and/or size. 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 1974, Chakraborty et al. suggested that genetic testing via electrophoresis had advanced such that this method might be used to confirm paternity rather than merely exclude a man as a child’s father.

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 99.99% (i.e., 9,999 out of 10,000). 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.

The Utility of Paternity Testing
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 1980s and 1990s, 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 99.99% accurate and applicable in a variety of settings. 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.


Impacts on paternity test immediately after child birth

Paternity testing can change the life of a child as well as the lives of the adults tested. Paternity testing provides highly accurate results within a few days. A rushed sample can be completed in as little as one to three days, Identigene reports, meaning that, in many cases, an answer regarding paternity can be provided before the baby leaves the hospital.

DNA samples obtained from the child’s mother and alleged father often come from a simple swab of the inside of the cheek, which removes cells for testing. A newborn’s cord blood can be used for his sample, or a cheek swab can also be used. Samples can easily be obtained before the baby leaves the hospital. Samples are taken at a testing facility or done by the alleged father and the mother and sent in to the laboratory for testing in special sample kits obtained at the pharmacy. If testing is done at a laboratory, identification to ensure a person is who he says he is must be presented.

A paternity test resembles a puzzle where pieces from the parents and child must match. DNA tests compare 15 DNA markers of both parents to those of the child. While testing can be done without the mother’s DNA, her sample makes testing simpler and slightly more reliable. Since a child inherits genes from each parent, each locus, or marker location, must show one allele inherited from the mother and one from the father. If three or more DNA markers don’t match between the alleged father and child, that person can’t be the father of the child, IdentiGene explains, even if several other items do match. Almost any two people will have some matches.

A positive result depends not just on the number of allele matches but also on the probability of two people having the particular match. Some DNA matches are rarer than others and are assigned a higher value, called a paternity index, or PI value. Adding all the PI values together gives a combined paternity index, or CPI. A CPI of 100 indicates a 99 percent probability of paternity on an accredited paternity test report, which courts require for child support cases. Immigration cases require a CPI of 200, or 99.5 percent, according to IdentiGene. Reports don’t claim a person is the biological father; instead, they state the person is not excluded as the father.

Time Frame
If a decision on paternity must be obtained before a child is discharged from the hospital, prenatal testing can be done, so that the results are known before the baby is born. Amniotic fluid cells or cells from near the placenta are removed and sent to the lab. This procedure is expensive and carries some risk to the fetus, says the American Pregnancy Association.

DNA testing can’t distinguish between identical twin brothers as to which one is the father of the child, since identical twins carry the exact same DNA makeup. If the alleged father has died, samples from his parents can be used for testing, but only if his parentage is absolutely known. If his legal father was not his biological father, testing won’t be accurate, Genelex warns.