DNA paternity testing
DNA paternity testing uses DNA profiles to determine whether an individual is the biological parent of another individual. Paternity testing can be essential when the rights and duties of the father are in issue, and a child's paternity is in doubt. Tests can also determine the likelihood of someone being a biological grandparent. 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 paternity testing techniques are polymerase chain reaction and restriction fragment length polymorphism. Paternity testing can now also be performed while the woman is still pregnant from a blood draw.
DNA testing is currently the most advanced and accurate technology to determine parentage. In a DNA paternity test, the result 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. This can lead to complications during DNA analysis, such as false negative results if their reproductive tissue has a different genetic makeup from the tissue sampled for the test.
Paternity or maternity testing for child or adult
The DNA test is conducted by collecting buccal cells found on the inside of a person's cheek using a buccal or cheek swab. These swabs have handles made of wood or plastic with a cotton synthetic tip. The collector rubs the inside of a person's cheek to collect as many buccal cells as possible, which are then sent to a laboratory for testing. Samples from both the alleged father or mother and the child are required for the test.Prenatal paternity testing for unborn child
Invasive prenatal paternity testing
It is possible to determine who the biological father of the fetus is while the woman is still pregnant through a procedure known as chorionic villus sampling or amniocentesis. Chorionic villus sampling retrieves placental tissue, which can be done either through the cervix or the abdominal wall. Amniocentesis involves collecting amniotic fluid by inserting a needle through the pregnant mother's abdominal wall. Both procedures are highly accurate because they obtain samples directly from the fetus. However, there is a small risk of miscarriage associated with them, which could result in the loss of the pregnancy. Both CVS and amniocentesis require the pregnant woman to consult a maternal-fetal medicine specialist who will perform the procedure. CVS testing can be taken from as early as 10 weeks into pregnancy and an amniocentesis test can be performed between 14 and 20 weeks of pregnancy.Non-invasive prenatal paternity testing
Recent advances in genetic testing have led to the ability to identify the biological father while the woman is still pregnant. A small quantity of cell-free fetal DNA is present in the mother's blood during pregnancy. This allows for accurate paternity testing during pregnancy from a blood draw without any risk of miscarriage. Research indicates that cffDNA can first be detected as early as seven weeks into the pregnancy, and its quantity increases as the pregnancy continues.DNA profiling
The DNA of an individual is identical in all somatic cells. During sexual reproduction, the DNA from both parents combines to create a unique genetic makeup in a new cell. As a result, an individual's genetic material is derived equally from each parent. This genetic material is referred to as the nuclear genome because it is located in the nucleus of a cell.Autosomal DNA testing allows for a comparison between the child's DNA, the mother's DNA, and the alleged father's DNA. By examining the genetic contribution from the mother, researchers can determine possible genotypes for the actual father. Specific sequences are examined to see if they were copied verbatim from one individual's genome; if so, then the genetic material of one individual could have been derived from that of the other. If the alleged father cannot be excluded as the true father, then statistical analysis can be performed to assess how likely it is that the alleged father is the true father compared to a random man.
In addition to nuclear DNA, mitochondria contain their own genetic material known as mitochondrial DNA. This mitochondrial DNA is inherited solely from the mother and is passed down without any mixing. As a result, establishing a relationship through the comparison of the mitochondrial genome is generally easier than doing so with the nuclear genome. However, testing the mitochondrial DNA can only confirm whether two individuals share a maternal ancestry; it cannot be used to determine paternity. Therefore, its application is somewhat limited.
In testing the paternity of a male child, the Y chromosome can be used for comparison, as it is inherited directly from father to son. Like mitochondrial DNA, the Y chromosome is passed down through the paternal line. This means that the two brothers share the same Y chromosome from their father. Therefore, if one brother is the alleged father, his biological brother could also be the father based solely on Y chromosomal data. This holds true for any male relative related to the suspected father along the paternal line. For this reason, autosomal DNA testing would provide a more accurate method for determining paternity.
In the US, the AABB has established regulations for DNA paternity and family relationship testing, although AABB accreditation is not mandatory. DNA test results can be considered legally admissible if the collection and processing adhere to a proper chain of custody. Similarly, in Canada, the SCC has regulations on DNA paternity and relationship testing, while accreditation is recommended, it is not required.
The Paternity Testing Commission of the International Society for Forensic Genetics is responsible for creating biostatistical recommendations by the ISO/IEC 17025 standards. Biostatistical evaluations of paternity should be based on the likelihood ratio principle, resulting in the Paternity Index. These recommendations offer guidance on the concepts of genetic hypotheses, calculation concerns necessary for producing valid PIs, as well as addressing specific issues related to population genetics.
History
Parental testing has evolved significantly since the 1920s. The earliest method was blood typing, relying on the inheritance of blood types discovered in 1901. In blood typing, the blood types, of the child and the alleged parents are compared to assess the possibility of a parental linkage. For instance, two type O parents can only have type O children, while type B parents can have type B or O offspring. However, this method was limited, excluding about 30% of potential parents based solely on blood type.In the 1930s, serological testing improved the process by examining proteins in the blood, with an exclusion rate of around 40%. The 1960s brought Human Leukocyte Antigen typing, which compared genetic markers in white blood cells, achieving about 80% accuracy but struggling to differentiate between close relatives.
The 1970s saw advancements with the discovery of restriction enzyme, leading to Restriction Fragment Length Polymorphism testing in the 1980s, which offered high accuracy. By the 1990s, Polymerase Chain Reaction became the standard, providing faster, simpler, and more accurate results with exclusion rates of 99.99% or higher, revolutionizing parental testing in both legal and familial matters.
Legal evidence
A DNA parentage test that adheres to a strict chain of custody can produce legally admissible results used for various purposes, including child support, inheritance, social welfare benefits, immigration, and adoption. To meet the chain-of-custody legal requirements, all tested individuals must be properly identified, and their specimens must be collected by an independent third-party who is not related to any of the tested parties and has no interest in the test's outcome. The quantum of evidence needed is clear and convincing evidence, meaning that it is more substantial than in an ordinary civil case but less than the “beyond a reasonable doubt” standard needed for a criminal conviction.In recent years, immigration authorities in multiple countries- including the United States, United Kingdom, Canada, Australia, France, and others, may accept DNA parentage test results from immigration petitioners and beneficiaries in a family-based immigration case when primary documents that prove biological relationships are missing or inadequate.
In the U.S., it is the responsibility of immigration applicants to arrange and cover the cost of DNA testing. U.S. immigration authorities mandate that any DNA test performed must be conducted by a laboratory accredited by the AABB. Similarly, in Canada, the laboratory must be certified by the Standards Council of Canada.
Although paternity tests are more prevalent than maternity tests, there are situations where the biological mother of the child is uncertain. Examples include cases in which an adopted child seeks to reunite with their biological mother, potential hospital mix-ups, and in vitro fertilization scenarios where an unrelated embryo may have been implanted in the mother.
Other factors, such as new laws regarding reproductive technologies involving donated eggs and sperm or surrogate mothers, can also complicate the determination of legal motherhood. For instance, in Canada, the federal Human Assisted Reproduction Act allows for the use of hired surrogate mothers, meaning that the legal mother may be the egg donor rather than the woman who gave birth. Similar laws exist in the United Kingdom and Australia.
In Brazil in 2019, two male identical twins were ordered to both pay maintenance for a child fathered by one of them because the father could not be identified with DNA.