Can Direct-to-Consumer Genetics Tests Provide Accurate Results?
First, How Does Paternity Testing Work?
Paternity testing, like other forms of familial testing (sibling, maternal, etc.) is a relatively straightforward practice. Other forms of DNA analysis rely on understanding the genes involved and their relationship with disease. In paternity testing, scientists are simply checking to see if the DNA matches in various locations.
To understand how this process can identify someone as a direct family member, you must understand a little bit about genetics. A human starts as two different cells, the sperm and the egg. Inside of these cells is exactly half of the DNA necessary to create a human. Both cells contain 23 chromosomes, or parts of DNA.
Half Mom, Half Dad
The chromosomes inside of the egg have a matching chromosome within the sperm. When they fuse together during fertilization, the single cell created has 46 chromosomes in 23 pairs. This cell then replicates, grows, and replicates many times. Cells differentiate into specific tissues and organs, and a multicellular human is born into the world. Each of your cells contains a copy of the original 46 chromosomes.
In other words, you share half of your DNA with your father, and half with your mother. Without knowing any of the specific genes within your DNA, a laboratory can tell if you are related to someone directly.
To do this, they simply “read” the DNA at many locations. They do this on your DNA, then on the other DNA sample you present. If all of the spots are exact matches, it is extremely likely that you inherited the DNA from that person, or they inherited it from you. If the locations are not a match and you share much less than half of the tested locations with the other sample, you are likely not related to the person.
How Accurate is Paternity Testing in General?
In this case, likely is a very strong word. With greater than 99% accuracy, the results can be considered valid. The reason is biological. First off, the only thing that can change your DNA is a mutation. This might show a false-positive, if the stars lined up. In this case, the lab would assume two people are related. In actuality, the mutations could have changed your DNA to make it look like you are related.
This is highly unlikely. Scientists have measured the mutation rate, and have shown that there are on average only 175 mutations per person in the DNA code of over 6 billion nucleotides. Not only would all of these mutations have to occur, but they would have to land specifically on the DNA portions that the laboratory is testing. Even then, the mutations would have to be the correct nucleotide (1 of 4) to match the other sample. The statistical probability of a good paternity test being a false-positive is mind-numbingly low.
The only other possibility of really confusing a paternity laboratory is to have the DNA of an identical twin. If that is the case, the two individuals share the same DNA. It would be really hard to tell who the father was, as the genetic tests would look the same.
Besides these two exceedingly unlikely situations, paternity tests are very accurate. Many genetic testing companies, such as 23andMe, offer paternity and sibling testing as feature of their platform. Because they already test so many spots within your DNA, the test becomes easy to conduct. Further, as one of the first forms of genetic testing, paternity tests have become readily accessible and fairly cheap. They can even be found at Walgreens and Walmart.
Should I use an At-Home Paternity Test?
There are various upsides and downsides to at home paternity and familial relationship tests. In most versions, you buy a kit online or in the pharmacy. You swab your cheek cells, and those of the other person being analyzed. You send the kit to the laboratory, where the DNA samples are analyzed.
Paternity testing is relatively simple compared to other forms of genetic analysis, and many companies offer safe and effective methods for testing paternity. Whether or not you should use an at-home test depends a lot on your motivations.
If you’re trying to prove that your sibling is actually adopted, these tests would be a fairly way cheap to get some quick answers. If you are getting a paternity test in a complicated legal battle, you might have to do your research to make sure the evidence will be admissible.
What is the Legality of Paternity Testing?
In the United States, the legality of paternity testing is complicated. Any parent can test their children for paternity, and can do so using an at-home paternity test. However, if the results are to be used for legal matters, most at home kits are not admissible in court. This is not because the tests are necessarily less accurate, but simply because the courts require chain-of-custody, discussed below.
In each state, the rules can vary even more. Some courts require that paternity testing is done by the laboratory they normally work with. Other states require that any lab can be used, as long as it is accredited under the ISO/IEC 17025 standard. Many labs carry this standard and there are more than half a dozen certifying agencies. Typically, the paternity test is ordered by the court, and processed at a lab of their choosing. United States Immigration proceedings require that the tests be performed by an AABB accredited lab. A list of these labs can be found here.
Under Canadian laws, paternity testing is regulated to accredited labs only. While personal paternity testing kits can be found and purchased, the government recommends that testing is only done in accredited labs.
Within Canada, two bodies are solely responsible for accrediting laboratories. The Standards Council of Canada and the Canadian Association for Laboratory Accreditation also certify laboratories to the ISO 17025 standard, which is a general laboratory competence standard.
Like US and Canadian laws, there are little to no restrictions on personal paternity tests. They can be purchased and analyzed by a variety of companies and laboratories. However, when it comes to court-ordered paternity tests, only laboratories accredited by the Ministry of Justice. A full list of testing laboratories and information about getting a paternity test in the UK can be found here.
Non-admissible paternity tests are readily available in Australia, as in the other countries above. Australia has specific laws regarding paternity testing, and all testing must comply with the Family Law Regulations 1984. According to those rules, the lab which completes the test must be accredited by the National Association of Testing Authorities.
Are Cheaper Private Tests as Good as Accredited Labs?
This depends on the company, but many companies claim that their results are accurate and accepted in courts. Many companies market separate versions of their product for this purpose. A court-admissible test is almost always administered by a third-party to insure the samples are not tampered with. The third-party also verifies the identities of those involved, to insure the results. This is a common law practice to document the process, known as chain-of-custody.
If you don’t need the results to stand up in court, and don’t want to pay extra for someone else to swab your cheek, the results are just as accurate in the regular versions. The lab will likely use the exact same process to analyze both types of sample.
If you do need the results to stand up in court, definitely look for a company which offers services through a third-party tester. This may be more expensive, but it certifies the results with an independent laboratory, insuring the judge will accept the evidence.
What’s the Difference between Take Home Tests and Tests Performed at a Lab?
To be honest, this is a complex question to answer. In short, they are similar but a professional lab dedicated to court-admissible tests will be more rigorous.
Unfortunately, no paternity tests are regulated by the FDA. This has allowed many companies to market products which actually only test a few sites within the DNA. This greatly lowers the accuracy and validity of the test.
Paternity labs often cost more, but there are several benefits. The evidence chain-of-custody is secured, for the purposes of court cases. The lab may also offer a higher level of analysis, though direct-to-consumer tests are rapidly catching up.
Sites like 23andMe automatically find other relatives on the platform, based on paternity testing. Though the results from these sorts of matches has yet to be tested thoroughly in court, the results are scientifically accurate. Many direct-to-consumer genetics testing kits include this aspect, simply as a byproduct of analyzing other genes.
- Hartwell, L. H., Hood, L., Goldberg, M. L., Reynolds, A. E., & Silver, L. M. (2011). Genetics: From Genes to Genomes. Boston: McGraw Hill.
- Estimate of the Mutation Rate per Nucleotide in Humans | Genetics. (n.d.). Retrieved December 6, 2018, from http://www.genetics.org/content/156/1/297.short
- Paternity testing under the cloak of recreational genetics | European Journal of Human Genetics. (n.d.). Retrieved December 6, 2018, from https://www.nature.com/articles/ejhg201731
- DNA paternity testing. (2018). In Wikipedia. Retrieved from https://en.wikipedia.org/w/index.php?title=DNA_paternity_testing&oldid=869598589