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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 questions 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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