Restriction Fragment Length Polymorphism (RFLP) in DNA Testing
What is RFLP?
Restriction fragment length polymorphism, or RFLP
,
is a technique for preparing a DNA sample for analysis through electrophoresis.
How does it work?
The DNA sample is exposed to restriction enzymes that recognize and cut DNA at specific sequences surrounding variable number of tandem repeats,
or VNTRs. VNTRs are short sequences of DNA that repeat a specific number of times, based on inheritance. When the restriction enzymes cut the DNA sample,
the products are DNA fragments of different lengths. The fragments are further analyzed through
electrophoresis
.
In DNA paternity testing using RFLP, a child's DNA is cut into fragments that match the biological parents' DNA fragment lengths. Half of
the child's DNA fragments will be the same length as the mother's DNA fragments, while the remaining fragments will be the same length as the father's
DNA fragments.
Sometimes a child will have fragments that do not match either biological parent. When this happens, the lab will perform additional statistical
analysis to determine if an unmatched fragment was caused by a mutation or if the tested father is not the child's biological father.
Why use RFLP?
RFLP has a high
power of exclusion
, typically equal to or higher than 99.99%.
Through RFLP, labs are able to analyze samples with a high power of discrimination at fewer
loci
(usually 6 loci) than other tests require.
This means that they only have to use a few loci instead of using as many as 14 to obtain conclusive results.
Despite its power, the RFLP technique is not as common as PCR. It requires large samples of blood from tested parties and can take up to 8 weeks
for analysis. Since the advent of PCR technology, many laboratories have favored the use of small buccal samples and the fast turnaround time made possible by PCR.
Additionally, PCR offers a similar and often greater power of exclusion.
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