Notesale: Turn your study into money

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Applications of reproduction and genetics
Conventional breeding techniques were previously used to improve farm animals, crops and
ornamental plants
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Embryo surgery can increase a farmer’s stock
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Eggs are taken from high milk yielding cow which has been hormonally treated to super
ovulate
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The
fertilised egg divides to form a ball of cells (totipotent) which is split into separate cells
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Embryos are then transplanted
into surrogates hormonally treated for the oestrus cycle to synch to be ready to receive an embryo
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Advantages
 The reproductive rate of the genetically superior female is considerably increased
 The genetically superior female isn’t put at risk by becoming pregnant
 Transplanted embryos can be sexed and tested for genetic diseases pre-implantation,
increasing the good offspring
 Embryos can be transferred to a small mammal (rabbit)- portmanteau animal- for global
transport and the embryos recovered and reimplanted into hormonally prepared surrogates
 Surrogates may be a different species (horse- zebra), important for breeding rare animals
Disadvantages
 Ethical objections as animals are denied natural instincts and behaviour and are used by the
breeder as the means to an end
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Donor cells were taken from the udder tissue of a ewe and cultured for a week in low
nutrient medium to stop them dividing
An unfertilised egg was removed from another ewe and the nucleus with DNA was removed
with a micropipette leaving an enucleated egg cell
The dormant donor cell and recipient egg cell were placed close together and fused using a
very gentle electric pulse
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Advantages
 Desirable qualities are preserved for future generations

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Cell culture is useful for production of cells in quantity- cancer cells for medical research,
monoclonal antibodies
Enables production of many genetically identical copies of an animal
Conserves unique features
Useful for production of cells in quantity
Producing a single identical genetic line of cells with desirable characteristics maintains
genetic stocks

Disadvantages
 Cross breeding reshuffles genes so desirable characteristic may be lost
 In mammals it is expensive and unreliable with a low success rate; 3% in mice
 Inadvertent selection of disadvantageous alleles is possible
 Progeny may show long term unforeseen effects such as premature ageing
Tissue culture
Cells from young animals and cancer cells can be induced to divide in vitro
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g
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Most cells differentiate to cells with specific
functions e
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nerve cells, muscle cells and most of these don’t normally divide again
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The medium the cells grow in is closely controlled and
conditions (water potential, temperature) are carefully monitored
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All the cells are
identical and contain identical genes to the parent cell
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Artificial skin (apligraf) widely used instead of skin grafts
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 Stem cells are undifferentiated dividing cells that are found in adult animal tissues and need
to be constantly replaced
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g
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They can
develop into any other types of cell in the right conditions
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Stem cells are also found at the earliest stages of embryo
development before the cells have differentiated- embryonic stem cells
 Therapeutic stem cell cloning could be used to generate organs for transplant which would
prevent immune rejection and reduce problems of organ shortages
o A mature cell is taken from the patient and the nucleus is removed
o The nucleus is removed from the human ovum
o The mature nucleus is transferred to the enucleated ovum, and then divides forming
a ball of stem cells
o Stem cells are isolated and cultured with appropriate growth factors allowing them
to grow into the required organ or tissue

Ethics of stem cell use
Embryonic stem cell research is currently allowed in the UK under license
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When the stem cells are removed, these
embryos would be destroyed
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Others consider the potential benefits outweigh the ethical
concerns
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Stem cells can be obtained from human adults bone marrow with no consent required
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Opponents argue embryonic stem cell technologies could lead to reproductive cloning and
fundamentally devalue human life
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Micropropagation (plant tissue culture)
Cloning of plants is a very cost effective way to produce many genetically identical plants which are
clones of a single parent
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In
the right conditions, many plant cells can develop into any other cell
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If cells are removed from the meristem and placed in suitable conditions, new, genetically
identical plants will develop
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A plant with desired characteristics is chosen
A sterile scalpel is used to remove the meristem from the shoot
The meristem is cut into small pieces called explants
The explants are placed onto a sterile aerated nutrient medium e
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agar with nutrients and
hormones to encourage shoot growth
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The callus is subdivided and each piece is allowed to differentiate into a plantlet
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Regular inspections are needed to remove defective
individuals, increasing labour costs above traditional propagation methods
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The project is complete but it may take years to analyse the data
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Aims:
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Identify all 20,000-25,000 genes in human DNA
Determine the sequences of the 3 billion chemical base pairs that make up human DNA
Store this information in databases
Improve tools for data analysis
Transfer related technologies to the private sector
Address ethical, legal and social issues that may arise

The information enables scientists to know exactly which sections of DNA, on which chromosomes,
are responsible for the many different inherited diseases:
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A sample is taken from a patient and scanned for mutated sequences
Gene probes (short piece of DNA the sequences of which are complementary to the
mutated sequences) are used to seek their complement in the 3 billion base pairs of an
individual’s genome
if the mutated sequence is present, the probe will bind to it and flag the mutation

Another method of DNA testing involves comparing the DNA bases sequence in a patient’s gene to a
normal version of the gene
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Medical implications of the human genome project:
 All diseases have a genetic component- inherited or due to environmental stress e
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viruses,
toxins, mutagens, radiation
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Prediction- detecting errant genes in genomes helps predict disease in later life
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Detecting errant genes affects families
as the genes may have been or be inherited

Genetic screening- the screening of humans for specific mutations that are known to cause disease
or increase the risk of disease, a DNA or genetic probe is often used to identify the presence of the
mutant allele responsible for the condition
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This could alter decisions as to whether to have children
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The environment (diet, smoking) also plays a role in disease development
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Those at greatest risk can be
targeted by health authorities for regular screening and appropriate advice to reduce risk
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When
protein structure is known, one can design drugs with molecules that fit to potentially design
drugs to act against the gene
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The
tests give a probability for developing the disorder
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Mutations work together with other
unknown mutations or environmental factors to cause disease
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Gene therapy replaces a defective gene with a
gene cloned from a healthy individual to give a potential cure for a genetic disorder
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Gene therapy usually requires a vector or carrier to introduce DNA
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Some use liposomes, others use
injection of naked plasma DNA
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Somatic cell therapy targets cells in the affected tissues
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Germ-line therapy involves introduction of corrective genes into germ-line cells; the gene is
replaced in the egg and enables genetic corrections to be inherited
Cystic fibrosis
Cystic fibrosis occurs because of a defective autosomal recessive allele
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Sufferers produce thick, sticky mucus from epithelial cells lining some
bodily passageways
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The mucus
is difficult to remove and causes recurrent infection
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The sufferer also has impaired digestion and limited food absorption
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To inherit the disease, both parents must carry the recessive allele
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The normal gene codes for the production of a protein found in the cell membrane
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Sodium ions flow from the cells and water passes out of cells by osmosis
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The protein of those with cystic fibrosis lacks one amino
acid so it cannot perform its function
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There are two
methods to deliver to the epithelial cells of the lung:
1
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These cells start to express the inserted gene by making protein CFTR
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Only a
small proportion of the introduced genes are expressed
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Genetic counselling
If there’s family history of a genetic defect, unaffected members can get advice on risk of bearing an
affected child
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This enables decisions about
themselves or potential offspring
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The parents can
then decide to terminate the pregnancy
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The
fluid contains cells that have floated away from the surface of the embryo
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 Chorionic villus sampling- early in pregnancy (8-10 weeks) tiny samples of foetal tissue are
withdrawn from the uterus and cells are cultured and examine under the microscope
Advantages of gene therapy:
 Couples can find out if they are carriers of a genetic disease and then decide if they want a
child that could be born with a defect
 Potentially more able to resist (carcinogens) in the workplace so employing them is cheaper
than installing expensive health and safety measures to avoid contact
Disadvantages:
 Invasion of privacy
 Finding defective genes may lead to increased abortions
 Individuals with defects may be placed in high risk groups for insurance to cover the cost of
treatment and may be denied insurance on the grounds it is unfair for those free on the
condition to support those with it e
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Huntington’s
 Denial of jobs because of susceptibility potentially meaning absence
 It is difficult to share the knowledge as it impacts friends and family
Genetic engineering
Genetic engineering allows genes to be manipulated, altered and transferred from one organism to
another
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Two methods of isolation can
be used with the enzymes restriction endonucleases or reverse transcriptase
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When added to the appropriate solution, the probe will match
and then bind to the gene of interest
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Restriction endonucleases cure the
DNA into small pieces, allowing individual genes to be isolated
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Most restriction enzymes split the two
strands in a staggered sequence; the unpaired bases at the cut form sticky ends
Reverse transcriptase:
The cell only has two copies of the DNA but may have many molecules of mRNA that has been
transcribed from it
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The functional mRNA coding for insulin is present in large quantities in
the cytoplasm of the pancreatic cells
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Reverse transcriptase, made from a group of viruses called
retroviruses, is used to make a DNA copy of the mRNA
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Many copies of cDNA are made
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Inserting the gene into the vector
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To insert the gene into a bacterium, a vector is used- here this is a plasmid (small circular
piece of DNA found in bacteria)
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The circular DNA molecule making up the plasmid is cut open using the same enzyme,
restriction endonuclease, which makes staggered cuts- sticky ends- to allow donor DNA to
be spliced into vector DNA
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The sticky ends are complementary and the C and G bases on their sticky ends pair up
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Transfer of DNA into the host cell and the use of genetic markers
The recombinant DNA must be transferred into bacterial cells
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As few as 1% of bacterial cells take up the plasmids, so these need to be identified, which involves
use of antibiotic resistant genes
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The technique is based on that some plasmids carry a gene for antibiotic resistance and this is
unaffected by the introduction of a new gene
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All bacterial cells are grown on a medium with the antibiotic, ampicillin
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These bacterial cells can
break down the antibiotic and survive
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Cloning of the recombinant
containing bacteria causes production of multiple copies of the recombinant gene
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The genetically modified bacteria are cultured on a large scale using a fermenter and produce insulin
which is extracted and purified
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Identification and isolation of the gene- The gene for insulin can be identified and isolated by
starting with mRNA (made by transcription)
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Isolation of this gene from the rest of the DNA
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Insertion of the gene into a vector to transfer it to the host cell (virus or plasmid)
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Identification of host cells which have successfully taken up the gene
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Production of the desired protein by the host cell
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Purification of the protein for clinical use
Advantages
 Large quantities of complex proteins can be made, not possible by other methods
 No need to extract organs from other mammals
Disadvantages
 Technically complicated and expensive on industrial scale
 Difficult to identify the valuable genes
 Synthesis of a required protein may involve several genes each coding for polypeptide
 Treatment of human DNA with restriction endonucleases produces millions of useless
fragments
 Not all eukaryotic genes express themselves in prokaryotic cells
 Hazards:

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Bacterial readily exchange genetic material
Deliberate use of antibiotic resistance genes may cause the wild population to
develop antibiotic resistance
Increased cancer risk if oncogenes spread from lab to wild populations

Genetically modified organisms
The techniques described previously can be used to alter the genetic make-up of plants and animals,
by the transfer of genes between individuals of the same or different species
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Genetic engineering allows selection, isolation, and
insertion of desirable genes into plants
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Genes can be isolated and inserted into a vector, normally from a bacterium
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Useful genes (virus resistance) can be added to the Ti plasmid before it is reinserted into the
bacterium and used to infect the plant
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Examples under trial or commercial use:
o Glyphosphate (herbicide) resistance in maize, soya bean and others- reduces herbicide use
o Insect resistance using the gene for Bt toxin protein
o Virus resistance
o Ability to produce human interferon
o Ability to produce human antibodies
o Research into vaccine for malaria- e
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in bananas
Genetically modified crops
Bacteria are readily introduced into plants
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This is because the bacteria insert genes from their plasmids into one
of the plant’s chromosomes
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Scientists can replace tumour-forming genes in the bacterial plasmids with useful genes
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g
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Tomatoes ripen naturally as they produce an enzyme to break down the pectin in
their cell walls
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Scientists have developed a genetically modified tomato
called ‘Flavr Savr’
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The mRNA transcribed from the inserted
gene is complementary to the mRNA strand of the original gene
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This prevents mRNA of the original gene from being translated and effectively blocks the
production of the enzyme
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Oppositions to GM crops:
 GM plants by pollination could transfer their genes to wild relatives or similar nearby crops
with unforeseen effects
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g
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Long-term field trials are
establishing if these concerns are well-founded
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There’s a concern these
genes could be transferred to the bacteria in the intestine of the consumer
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Plants could then be more susceptible to attack by pests and
diseases and lead to a reduction in the use of important old varieties of their wild relatives
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Polled from GM crops could enter organic fields and beehives via wind and insects
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E
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disease resistance in otherwise
vulnerable animals
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Genetic fingerprinting
Your genetic fingerprint is your DNA profile, which is unique
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Exons code for
proteins
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Individuals acquire different
sequences of introns, non-functional DNA with varying length but 20-40 bases long, often repeated
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It is the number of times that these are repeated that shows differences
between individuals, and is inherited
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DNA is extracted from the sample and PCR is used to make more copies
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DNA fragments are separated by gel electrophoresis
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The smaller the fragment, the faster it moves,
so the DNA becomes separated into bands according to size

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A layer of absorbent paper is added and DNA is drawn up of the nylon
membrane by capillary action
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DNA fragments are denatured by heating, giving single stranded DNA
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The probe binds with its complementary single
stranded DNA and any unbound fragments are washed off
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This autoradiograph reveals a pattern of light and dark bands (dark
is where radioactive probe is present) which are unique to individuals- genetic fingerprints
Polymerase Chain Reaction
PCR is essentially semi-conservative replication
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Reaction requirements:
o DNA template with the target sequence you want to amplify
o Deoxyribonucleotide triphosphates- adenine, guanine, thymine and cytosine to make new
DNA copies
o Oligonucleotide primers- a pair of short strands of single stranded DNA complementary to
the ends of the DNA template
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o DNA polymerase synthesises new copies of DNA, referred to as Taq polymerase because
thermus aquaticus bacterium is used

DNA template molecules

Following extension, there are two copies of
the target DNA for each original copy
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The number then doubles again causing
exponential increase
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The DNA is now
denatured
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Extension continues for as long
as it takes to copy the length of target DNA
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Excess of primers prevents DNA duplexes
from reforming
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Benefits
 Many GM organisms are kept in industrial fermenters (bacteria) or enclosed fields (sheep)
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 UK has strict guidelines on regulating release or trial of GM plants
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A native week with a gene not previously
transferred is high risk
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 Production of human hormones, antibiotics, and vaccines
 Antitrypsin coding gene (treats cystic fibrosis) has been transferred to sheep for milk
production with it; extracted by purification
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 Improved flavour and shelf life
 Crops can be developed with herbicide and pest resistance e
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transfer of genes producing
toxins with insecticidal properties from bacteria to higher plants such as potatoes
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g
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Hazards
 Seen by many as unnatural and unsafe as long term effects are unknown
 It is more difficult to contain GM crops or GM organisms used for biological pest control
 The modified plant could become an agricultural weed or invade natural habitats
 The introduced genes could be transferred by pollen to wild relatives whose hybrid offspring
may become invasive- pollen drift
 Introduced genes could be transferred by pollen to unmodified plants on an ‘organic’ farm
 Modified plants could be a direct hazard to humans or animals by being toxic or producing
allergens
 The herbicide currently used on the GM crop could leave toxic residues in the crop
 Research shows the risk of pollen drift is real and safe planting distances should be in excess
of 4000m (distance bees can forage) to maintain organic farms
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There’s a risk they could be transferred to other bacteria, adding to the problem of
antibiotic resistance
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Therefore crops could be more susceptible to pest
or disease attack causing use reduction of important old varieties or their wild relatives
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Those with genetic imperfections shouldn’t be socially deprived, traumatised or stigmatised
o Reliability and usefulness of foetal genetic testing
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Are genetic tests reliable and interpretable by professionals? Currently very little
quality control which is needed with standards
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o Parents testing children for adult onset diseases, especially with no available treatment or
there are uncertainties with conditions linked to multiple gene and environment interactions
o Do genes determine behaviour or can people always control it
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