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Analysis of DNA used in Forensic Science
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Produce a laboratory book that records your practical work on DNA analysis
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Lab reportIntroduction
Almost all cells that make up the human body are diploid, with the exception of gametes and red blood
cells. There are several types of biological evidence that are commonly used in forensic science for DNA
analysis, including blood, sperm, saliva, hair, bones and teeth, and some others, and some can be more
effective than others. Biological evidence in DNA can vary in areas including blood typing, chromosome
typing, DNA analysis and more recently DNA profiling. Since the introduction of DNA profiling in the 1980s,
it has been successfully used in criminal cases. To make sure that the DNA analysis is done correctly, we use
gel electrophoresis after the DNA has been extracted, and in fairness we use slab agarose gels to separate
the DNA, and because the gel is permeable, it allows DNA molecules to also move through it, the DNA is
negatively charged, so a charge is used on the agarose gel, which causes the DNA to move, which also
means it is attracted to the positive side. When a sample is collected, we have to get rid of the parts that
aren’t helpful, and we do this by using restriction enzymes to cut away the segments of the DNA that we
don’t want to use. The DNA is then amplified using PCR and gel electrophoresis is used to separate and
analyse the DNA sample and catch the correct suspect.
PCR analysis
The amount of DNA evidence collected during a crime investigation are often very small, amplification is
required for successful DNA analysis. Polymerase Chain Reaction (PCR) is a technique that allows the
amplification of DNA fragments. This means that a single copy of DNA fragment can be amplified into
millions of copies in a few hours. The requirements for a successful PCR are:
- A DNA template- the double stranded DNA that was separated from the sample
- DNA polymerase which consists of a thermostable Taq polymerase that doesn’t break down at high
temperatures
- Oligonucleotide primers which are complementary to the DNA target and mark the target that
needs to be amplified.
- Deoxynucleotide primers which are the single base pairs the build the DNA and give energy to
polymerisation.
- A reaction buffer- Magnesium Chloride is used to ensure the ideal conditions for the functioning of
the DNA polymerase enzyme, deoxyribonucleotides that build the DNA molecule and the template
DNA
The procedure
1. Denaturation- this entails the mix being heated to 96℃ for 15-20 seconds to denatures the DNA
strands which breaks down the bonds that holds the two strands together, giving us two separated
strands of DNA
2. Annealing- the reaction mix is cooled to 55-65℃, which allows the primers to bind to the areas
that want to be copied and now the specific areas of DNA can be targeted
3. Extending stages- here the reaction mix is heated to 72℃, this allows for Taq polymerase to find
the primers and start the copying process.
Gel electrophoresis method
Equipment list-
- Micropipette
- Gel tray - Fast blast stain
- Well combs - Bunsen burner and
- Painters tape - Conical flask
- 2% Agarose - Gloves
- DNA sample - Electrophoresis running buffer
- Voltage source - Scales
- Gel chamber - Measuring cylinder
- UV light
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