DNA Paternity Testing
Background and Technical Information

What Are Genes?

The human body consists of trillions of cells. Most of these cells have a nucleus, or center. The nucleus contains genes, the functional units of heredity. The genes are grouped into separate bundles called chromosomes.

There are 46 chromosomes inside every cell in the body. Twenty-three of these chromosomes came from the biological mother and 23 came from the biological father. Chromosomes are named by a letter "D" followed by a number [i.e., chromosome #1 is named D1; and, chromosome #2 is named D2, etc.]. Genes are named by the chromosome number, and by the location that the genes occupy on the chromosome. A DNA Parentage Test report identifies the genes that were analyzed during the process of testing. When the results refer to D2S44, the gene analyzed was on chromosome #2 at locus 44.

The Chemistry of Genes

Twenty-six letters of the alphabet are the basic units of the English language. Words and sentences are formed from these 26 letters. Genes on the other hand are formed from only 4 chemicals, or bases. These bases are named: (1) adenine, (2) cytosine, and (3) guanine and (4) thymine. Like the letters of the alphabet that form sentences, these 4 bases form long gene fragments called deoxyribonucleic acid, abbreviated DNA. The length of the gene fragments can be determined by the number of bases these gene fragments contain. When the gene fragment on a DNA Parentage Test report is 2.34 kilo bases that means the gene fragment consists of 2,340 bases [kilo base = 1,000 bases].

All children have a biological mother and a biological father. For each gene in the child, there is one genetic variant size that came from the father and one genetic variant size that came from the mother.  A DNA Parentage Test determines and examines the genetic variant sizes [i.e. allele sizes] found in the mother, the child and the alleged father.

In the sample report shown below, the upper gene fragment in the child (3.76-kb size) matches the upper gene fragment size of the mother. The child received the lower gene fragment (1.46-kb size) from his/her biological father.

The alleged father #1 has gene fragment sizes different from those found in the child. Therefore, the alleged father #1 cannot be the child's biological father. The alleged father #2 has the same gene size fragment as that found in the child (i.e., 1.46 KB). He could be the child's biological father. The probability that he is the child's biological father depends on the frequency with which this gene fragment is found in the male population. The fewer men who have this gene fragment size, the greater probability that the tested man is the biological father of the child.

This process is repeated several times and each time a different gene is analyzed. The accuracy of the DNA test results depends on the extent of the DNA Testing process. With sufficient testing, DNA technology provides an extremely powerful method of discriminating between fathers and non-fathers.