Paternity Tests: Blood Tests and DNA

Paternity refers to the legal process of identifying the father of a child generally through DNA testing. Paternity can be a factor in cases of child custody, child support, adoption and inheritance. The recent developments in DNA testing and other scientific methods of determining paternity have made it easier to establish paternity as required by state law. These tests are highly accurate and have an accuracy range between 90% and 99%. The can exclude the man who is not the biological father and if the samples match, the tests can calculate the likelihood of paternity. The “father”, the mother and the child should provide samples for testing. There several ways of testing paternity. The blood tests and DNA tests are the most common ones.

Blood Tests

To prove paternity, it wasn’t enough in most cases for the mother to simply testify that the defendant was the father. Occasionally, the physical appearance of the child was enough corroboration when unique hair or skin color, for example, was shared by the child and the defendant. More commonly, blood testing was used to make comparisons. By the seventies the courts accepted scientific tests to compare blood types of a mother, a child, and a suspected father. Using ABO blood typing and the analysis of other protein markers in blood, one could statistically show the relationships of a mother, a child, and a defendant. For many years these tests were the best means of proof at our disposal—but they ultimately proved to be a narrow scientific window into a far more powerful way of determining biological relationships.

Humans with blood group A posses the A antigen while those with blood group B posses the B antigen. Those will blood group AB possess both A and B antigen while those with blood group O possess neither. Antigens have genetic codes that are inherited. For example a child with blood group AB cannot have a mother with blood group B and father with blood group O. The father must have the A antigen. This type of testing was subsequently replaced in the 1970s by a more powerful Human Leukocyte Antigens (HLA) or white blood cell antigens. To perform this test, several milliliters of blood are needed. While blood tests alone cannot prove paternity, it can determine the possibility of fatherhood.

No blood or tissue test is 100-percent accurate in determining paternity. If properly collected and processed, however, scientific evidence can show with biological certainty when a man is not a child’s natural father. In attempting to demonstrate that a man is a child’s father, test results are used to formulate a “paternity index.”

Blood samples taken from the man and the child are subjected to a human leukocyte antigen test. Approximately, eighty markers within the blood’s white cells are studied and then compared with an index that weighs “plausibility of paternity” factors against a “cumulative chance of exclusion” indicator. If the index resulting from this procedure is 99.9 or higher, the man is presumed to be the child’s father.

DNA Tests

Because DNA tests can isolate a biological father’s “genetic finger- print,” DNA results are considered to be much more accurate than blood analyses, and in many jurisdictions, DNA evidence has replaced blood-test results as the primary indicator of paternity.

DNA is taken from the white cells present in a specimen of whole blood. Every person, except identical twins, has a unique genetic code, including a maternal allele and a paternal allele. If a child doesn’t possess the allele found in an alleged father’s genetic makeup, that man cannot be the child’s father. If the genetic codes match, a paternity index much more precise than the indicator used in blood tests is calculated to determine the likelihood of paternity. Unless blood and tissue samples have been collected and processed incompetently, DNA evidence is extremely difficult to refute.

The DNA testing is done using the Restriction Fragment Length Polymorphism (RFLP) blood test or the Buccal scrap procedure. The DNA sample is collected from the concerned parties by vigorously rubbing a swab against the inside of the cheek. DNA can also be collected from the umbilical cord blood specimen.

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