Paternity Testing in the Age of Dna
| Publication year | 1990 |
| Pages | 2061 |
| Citation | Vol. 19 No. 10 Pg. 2061 |
1990, October, Pg. 2061. Paternity Testing in the Age of DNA
Much interest and debate have arisen in the legal and scientific communities since the introduction of DNA identification techniques. The debate has focused primarily on use of the procedure as a forensic tool and on admissibility of DNA typing in criminal cases.(fn1) However, the application of the procedure in family law cases, particularly in paternity cases, should not be overlooked. Because of the alleged ability to determine with relative certainty whether a particular male is the father of a particular child,(fn2) the application of "DNA typing" will have a far-reaching impact on how attorneys handle paternity cases in the future. As a result, judges, attorneys and parties to paternity cases must understand the basic principles of the testing technique and the test's impact on the issue of paternity.
This article provides an overview of traditional methods used in paternity testing, reviews DNA typing as it applies to paternity testing and discusses admissibility considerations when DNA typing results are offered as evidence in paternity cases.
The human body is composed of more than 10 trillion cells. Most of these cells contain nuclei that house the heredity information encoded on a molecule known as deoxyribonucleic acid ("DNA"). Encoded on the DNA molecule is a complex set of instructions that directs the assembly and activities of cells in the body. Certain areas of these DNA instructions are unique and allow for specific individual identification.
DNA is packaged onto a specific in-tracellular structure known as a chromosome. Each cell contains forty-six chromosomes. At the time of conception, twenty-three chromosomes are derived from a person's mother and a matching set of twenty-three from a person's father. Thus, for each specific set of genetic information, there are two copies, one originally coming from the mother and the other coming from the father.
Each specific set of instructions is known as a gene, and each copy (maternal and paternal) is known as an allele. The DNA alleles can be identical, in which case the person is said to be homozygous, or they can be different, in which case the person is heterozygous. Each gene fits a precise chromosome location called a loci. Although most of the DNA is similar for different individuals, specific genes have been identified that vary considerably within the human population and are known as polymorphic loci.
In addition to being the hereditable material, DNA is also an information blueprint. All of the precise functions of each cell are directed through the translation of information found on the DNA molecule. This process occurs through the decoding of specific DNA information, known as its sequence, and the translation of the DNA sequence into another molecule, known as a protein or antigen. Because the protein or antigen structure is directed precisely by the DNA structure, there also exist polymorphic proteins and antigens that have been recognized on the surface of blood cells.
The basic strategy of all scientific laboratory tests used to evaluate paternity is similar. By comparing polymorphic antigens, proteins or DNA sequences, a scientist can determine those inheritance patterns consistent with a given alleged father being the biological father of a child. By comparing inheritance characteristics found in the child and its mother, a scientist can deduce those alleles or proteins which the child must have inherited from the biological father ("obligative genes"). If these genes are not present in the alleged father, he can be excluded as the biological father. However, if these genes are present, he is said to be included.
The effectiveness of each specific genetic trait for parentage testing is measured as the mean probability of excluding a falsely accused male ("PE"). For example, a genetic test of PE = 80 percent would exclude a falsely accused male as the father in 80 of 100 random males, but would falsely include him in 20 of 100 random males. Therefore, inclusion simply means that the genetic pattern is consistent with paternity. The weight of inclusion depends on the frequency of the particular genetic pattern as it is found in the general population.
Simply expressed, inclusion probability estimates the likelihood that a random male would fit the observed genetic pattern. This information is derived from extensive genetic testing of the human population which results in databases from which an estimate is made of the frequency with which given genes occur in a...
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