Paternity Test Glossary

The following are terms you might encounter when researching about paternity tests. Items in bold are also defined in this list.

Accreditation
Accreditation results from a successful completion of an inspection or audit by an accrediting body. Accreditation requires that the laboratory demonstrate and maintain good laboratory practices including chain-of-custody and evidence handling procedures. The gold standard for paternity tests is the accreditation provided by the American Association of Blood Banks.

Accuracy
A paternity test is considered accurate when proper procedures are followed to ensure that the results of the test are correct. At GeneSys, each sample is independently tested two times and the data are compared for consistency before reporting. The test results, reported as allele sizes, are objective measurements and are reliable, reproducible, and accurate.

Chain of Custody
The chain of custody refers to the specimen collection and documentation process that assures tested parties in a paternity test (and any judicial officials) that specimens were collected by a neutral party, were labeled properly, and were deliverd untampered. The Chain of Custody that will allow patients to take the case to court if needed.

Chromosome
Chromosomes are bundles of DNA molecules found in a cell, held together by proteins. There are 46 chromosomes in humans arranged in pairs, each pair consisting of one chromosome inherited from the mother and the other from the father. There are 22 pairs of non-sex chromosomes and 1 pair of sex chromosomes (XX or XY).

Combined Paternity Index (CPI)
The combined paternity index is the total measure of the strength of all the genetic evidence (allele size results) for a paternity test. The CPI is generated by multiplying the PIs from each locus.

DNA
Deoxyribonucleic acid (DNA) is a chemical substance found in cells of all living things. DNA, inherited from the biological parents, is the basis of heredity. It contains the code for all our physical attributes as well as the instructions for all functions of the body, including growth, development, and replication. DNA is composed of four different chemicals, A, T, C, and G, that function like letters in the code.

Exclusion
An exclusion result means that the DNA paternity test has revealed non-matches in the DNA profiles among the tested parties, and the biological relationship being tested is excluded (e.g. the alleged father is not the biological father).

Inclusion
An inclusion result means that the paternity test has proved to a reasonable degree that a biological relationship exists among the tested parties (e.g. the alleged father is the biological father).

Locus (plural loci)
A locus indicates the position of a gene on a chromosome. We use loci to describe the genetic markers we use for paternity testing: the D16S539 marker is on the 539th locus described on chromosome 16. The letters in the marker name provide other information about the DNA molecule where the marker is found.

Mutation
Genetic inconsistencies (mutations) occur naturally in all living organisms. When detected at the loci used for paternity analysis, these mutations have no effect on the individual. A genetic inconsistency is detected as a single mismatch between a child and the alleged parent. These results are factored into the final combined paternity index.

Paternity Test
A paternity test is a DNA test performed to determine the biological relationship between a child and the tested man. DNA from each individual is tested and the alleles at 15 DNA locations are identified and used to calculate a combined paternity index. Paternity tests are used as proof in obtaining child support, Social Security, and other benefits.

Paternity Index (PI)
A paternity index is the numerical indication of the strength of the genetic evidence in a paternity test. The number generated indicates the number of times more likely the alleged father is the biological father of the child than a random man in the population. A PI is calculated for each locus, and its magnitude is dependent on how common or rare the shared allele is between the AF and C. 

Probability of Paternity
The conversion of the CPI to a percentage is termed the probability of paternity.