DNA paternity testing

DNA paternity testing is the use of DNA profiles to determine whether an individual is the biological parent of another individual. Paternity testing can be especially important 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 techniques for paternity 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. DNA testing is currently the most advanced and accurate technology to determine parentage. In a DNA paternity test, the result (called the 'probability of parentage) 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 make-up from the tissue sampled for the test. The DNA test is performed by collecting buccal (cheek) cells found on the inside of a person's cheek using a buccal or cheek swab. These swabs have wooden or plastic stick handles with a cotton on 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 the alleged father or mother and the child would be needed. It is possible to determine who the biological father of the fetus is while the woman is still pregnant through procedures called chorionic villus sampling or amniocentesis. Chorionic villus sampling retrieves placental tissue in either a transcervical or transabdominal manner. Amniocentesis retrieves amniotic fluid by inserting a needle through the pregnant mother's abdominal wall. These procedures are highly accurate because they are taking a sample directly from the fetus; however, there is a small risk for the woman to miscarry and lose the pregnancy as a result. Both CVS and Amnio require the pregnant woman to visit a genetic specialist known as a maternal fetal medicine specialist who will perform the procedure. Current advances in genetic testing have led to the ability to determine who the biological father is while the woman is still pregnant through a non-invasive method. There is a small amount of fetal DNA (cffDNA) present in the mother's blood during pregnancy. This allows for accurate fetal DNA paternity testing during pregnancy from a blood draw with no risk of miscarriage. Studies have shown that cffDNA can first be observed as early as 7 weeks gestation, and the amount of cffDNA increases as the pregnancy progresses. The DNA of an individual is the same in every somatic (nonreproductive) cell. Sexual reproduction brings the DNA of both parents together randomly to create a unique combination of genetic material in a new cell, so the genetic material of an individual is derived from the genetic material of both their parents in equal amounts. This genetic material is known as the nuclear genome of the individual, because it is found in the nucleus. Comparing the DNA sequence of an individual to that of another individual can show whether one of them was derived from the other. However, DNA paternity tests are not currently 100% accurate. Specific sequences are usually looked at to see whether they were copied verbatim from one of the individual's genome to the other. If that was the case, then the genetic material of one individual could have been derived from that of the other (i.e. one is the parent of the other). Besides the nuclear DNA in the nucleus, the mitochondria in the cells also have their own genetic material termed the mitochondrial DNA. Mitochondrial DNA comes only from the mother, without any shuffling.