DNA from a Laboratory Perspective

How are the numbers in the Paternity Report chart derived?

The following illustration shows how the DNA results look after the samples are extracted, amplified, electrophoresed, and Genotyped®. The electropherogram data can be simply read without subjective interpretation by the analyst.

The first row is know as the Allelic Ladder and is comprised of common alleles (markers) in each Short Tandem Repeat (STR) system--the systems shown on this page are D3S1358, vWA, and FGA. The STR DNA Systems are arranged in columns.

The second row is the profile obtained from the alleged father--for D3S1358 he is a (14,17), vWA (17,20), and FGA (21,21).

Likewise, the third and fourth rows are interpreted in the same manner and are a samples from the child and mother. The black arrows indicate the alleles transmitted from the father and mother to the child. Note that in FGA the child received one copy of the 21 allele from the father and one copy from the mother.

The example is indicative of the tested man being the biological father...several other DNA systems are analyzed to increase the statistical strength to the paternity index.

The bottom row in this example is known as the positive control. The positive control is Genotyped® for each set of samples assuring accurate results. Not shown, but also run with each set of samples is the negative control and reagent blank... to make certain no extraneous DNA has found it's way into the process.

The following electropherograms are read in the same manner. The only addition (shown the next illustration) is "amelogenin". The amelogenin column is used for sex determination. Note that a sample of male origin will possess a "Y" Chromosome and be Genotyped® as a (X,Y) whereas the female sample will exhibit two copies of the X Chromosome (X,X).

The sample listed as "Child" is a male child as determined by amelogenin.