AQA A Level Biology - Gene Projects and Gene Technologies (2021-22)
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Course
Genome Projects and Gene Technologies
Institution
AQA
An in-depth informative booklet on Gene projects and Technologies, covering PCR, recombinant DNA technology and the benefits and risks, gene therapy, genetic fingerprinting etc. Includes useful summary questions and the specification for this topic.
Genome: The entire set of DNA, including all the genes, in an organism.
Genome Projects: Scientists work to determine the complete genome sequence of an organism. Their success
depends on the complexity of the organism and the technology that is available.
In vitro cloning:
In vitro cloning requires the use of the Polymerase Chain Reaction (PCR), which is an automated method of
copying fragments of DNA. The ingredients required are:
• The DNA fragment that is to be copied.
• Taq Polymerase (a type of DNA Polymerase) – this enzyme works the same as DNA Polymerase in
our cells, but is thermostable, so won’t denature at high temperatures.
• Primers – short sequences of nucleotides with a set of bases complementary to those at one end of
each of the two DNA fragments.
• DNA Nucleotides – used when the strands of the DNA fragments are being copied.
• Thermocycler – a computer-controlled machine that varies temperatures precisely over a period of
time.
PCR is carried out in three stages:
2
, 1. Separation of the DNA strand – All of the above components are added to the thermocycler and the
temperature is increased to 95°C. The two strands on the DNA fragment separate due to the breaking of
the hydrogen bonds.
2. Annealing (Binding) of the Primers – The mixture is cooled to 55°C. Primers bind (anneal) to their
complementary bases at the end of the DNA fragment. The primers allow the Taq Polymerase to bind
and start copying the DNA fragment, whilst also preventing the two separate strands from re-joining.
3. Synthesis of DNA – The temperature of the mixture is increased to 72°C. This is the optimum temperature
for the Taq Polymerase to add complementary nucleotides along each of the separated strands.
Advantages:
• It is extremely rapid – within hours, 100 billion copies of a gene can be made (each cycle takes
around 2 minutes). In vivo cloning could take days to obtain the same quantity of DNA.
• Living cells aren’t required – all that is needed is a base sequence of DNA. Therefore no complex
culturing techniques are required.
Sequencing Projects:
Genome projects are used to map the entire DNA nucleotide base sequence in a wide range of organisms,
from bacteria to humans. For example, the Human genome consists of over 3 billion base pairs, organised into
20,000 genes, taking 13 years to analyse!
DNA Sequencing - Whole Genome Sequencing (WGS):
1. DNA is cut into many small sections.
2. The small sections of DNA are sequenced using computers.
3. Computer algorithms are used to align overlapping segments in order to put the genome back together
in the correct order.
Important! – Sequencing methods such as these are continuously being updated which, along with the
increased automation of the processes involved, have led to extremely rapid sequencing of whole
genomes.
E.g. Sanger Sequencing vs Pyrosequencing.
Single Nucleotide Polymorphisms (SNPs):
• SNPs are single base variations that are
associated with diseases that have been
uncovered using DNA sequencing.
• Medical screening allows quick
identification of potential diseases and other
disorders, allowing early intervention to treat
them.
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