Biology Reference
In-Depth Information
4
DNA extraction
and quantification
DNA extraction has two main aims: first, to maximizing the yield of DNA from a
sample and in sufficient quantity to permit a full DNA profile to be obtained - this
is increasingly important as the sample size diminishes; and, second, to extract DNA
that is pure enough for subsequent analysis: the level of difficulty here depends very
much on the nature of the sample. Once the DNA has been extracted, quantifying
the DNA is important for subsequent analysis.
DNA extraction
There are many methods available for extracting DNA. The choice of which method
to use depends on a number of factors, including the sample type and quantity;
the speed and in some cases ability to automate the extraction procedure [1 - 5]; the
success rate with forensic samples, which is a result of extracting the maximum
amount of DNA from a sample and at the same time removing any PCR inhibitors
that will prevent successful profiling [2, 6 - 8]; the chemicals that are used in the
extraction - most laboratories go to great lengths to avoid using hazardous chemicals;
and the cost of the procedure. Another important factor is the experience of the
laboratory staff.
General principles of DNA extraction
The three stages of DNA extraction can be classified as (i) disruption of the cellular
membranes, resulting in cell lysis, (ii) protein denaturation and (iii) the separation
of DNA from the denatured protein and other cellular components. Some of the
extraction methods commonly used in forensic laboratories are described below.
Chelex
100 resin
The Chelex
100 method was one of the first extraction techniques adopted
by the forensic community. Chelex
100 is a resin that is composed of styrene -
divinylbenzene copolymers containing paired iminodiacetate ions [9]. The resin
