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DNA is extracted and purified (from the
buccal swabs, blood, etc.) using an enzyme which releases it
into solution. To determine sizes of DNA in a particular region
the DNA region is either:
- amplified using DNA primers,
targeted to the regions, and a DNA polymerase enzyme (PCR
method), or
- cut with restriction enzymes (RFLP
method).
The DNA samples are then ran on a
polyacrylamide gel to resolve sizes (Figure 1). A
computer-generated electropherogram (Figure 2) demonstrates how
the DNA sizes can be obtained using a fluorescent detection
system, similar to reading a barcode. To visualize the DNA,
either:
- the primers are labeled before the
PCR reaction, or
- a labeled probe is used to hybridize
to the specific region of DNA being examined (RFLP method).
Once the sizes of DNA in the specific
regions are determined, they are represented by a universal
number (e.g., 9, 10, 11), and referred to as alleles.
Each person should have 2 alleles at
each system examined for paternity testing (with exception given
to either, a) a person having the same allele presented twice,
or b) the possibility of a 'silent' allele). One allele is
passed from the biological father and the other allele is passed
from the biological mother. View the sample  Inclusion
Example and Exclusion
Example reports for more detailed descriptions.
Each known allele has a determined
frequency of occurrence in the general population and among
different ethnic groups (Table 1). These frequencies are used to
calculate the probabilities of paternity, siblingship,
grand-parentage, etc.
If you have any quesitons regarding
this process please let us know and we will be happy to assist
you with answering them.
| Figure 2: An electropherogram (or chromatograph)
showing the peaks that represent the 2 alleles
established at each chromosomal location tested for one
individual (i.e., D13S317, D7S820 and D16S539). In this
case, the data collected is that from Lane 2 (Child) in
Figure 1. |
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| Figure 1: An autoradiograph representing genomic DNA
sample detected using silver staining. Lanes labeled L
contain allelic ladders for the respective loci. Numbers
to the right of the image indicate the alleles
established for the samples ran in lanes 1 (Alleged
Father) and 2 (Child). |
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