of genetically modifying a plant genome
for enhanced characteristics - cloning plant cells, insect resistance,
herbicide resistance, improvements in nutritional value of food
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of biology notes on genetics and applications of GM biotechnology from
agriculture to medicine
of genetically modifying a plant genome
for enhanced characteristics
As we have seen, plants can be genetically modified to
enhance desired characteristics.
GM technology allows the transfer of useful
genes into plants, so they develop useful enhanced characteristics
e.g. anti-pest or increased size of grain.
GM crops are controversial but genetic engineering
is transforming crop production.
You can genes from all sorts of organisms, not
necessarily plants, cut out a selected chromosomes-genes, and insert
them into the cells of crop plants.
These crop plants are thus genetically
modified and referred to as GM crops.
You can genetically engineer crop plants to be
resistance to disease from e.g. viruses, increase crop yields,
produce bigger and better quality fruit.
A GM potato has been produced that is
resistant to potato blight, a disease caused by a fungus, that
devastated the rural population of Ireland in the 1840s who heavily
relied on the potato in their diet.
Note that when genes are transferred to
plants, it must be done at an early stage of their development
because older organisms have too many cells needing to be
The examples below
describe techniques used in agriculture to produce crops with desirable
characteristics that increase crop yields.
Example 1. Producing plant cell clones
Diagram showing the genetic modification of plant
cells using a bacterium plasmid vector, and finally cloning the plant cells
to produce a commercially viable plant on a large scale.
Scientists frequently use a bacterium call Agrobacterium fumefaciens to genetically modify plants.
The Agrobacterium fumefaciens bacterium
invades plant cells and can insert its genes into the plant's genome
With reference to the diagram above.
Stages 1. to 5.: A gene is taken from the
cells of a herbicide
resistant plant (B) and inserted into a
plasmid extracted from the Agrobacterium fumefaciens bacteria
The procedures use splicing genes to cut
the DNA strands open and join them up to make the modified
for even more details).
By this procedure, you can now introduce
the plasmid vector into the bacterium.
Stage 6.: The genetically modified plasmid is inserted back
into the bacterium.
Stage 7.: The bacterium, with the newly inserted gene, can
then enter the target plant cells and genetically modifies the plant
You quite simply let the modified bacterium
the plant cells, modifying their DNA.
Thus you can now clone the plant cells.
Stage 8.: BUT, you have to select the
correctly modified cells which have taken up the gene and reject the
rest of the cells.
After screening, the selected plant
cells are then grown into plantlets in a tissue culture
containing nutrients and growth hormones.
Stage 9.: The plantlets are then
trialled to produce fully grown mature plants.
Initially in a greenhouse, if successful,
full scale field trials using a much larger area.
The modified plant cells can then be used to grow
mature plants with their newly acquired gene giving them the
Example 2. Producing a crop plant with insect
A bacterium called Bacillus thuringiensis
produces a toxin (a protein) that is poisonous to insect larvae
that feed on plant roots and the adults on the leaves, damaging the
The gene in the bacterium that codes for the
toxin is inserted into the genome of crops such as corn and cotton.
The crops produce the toxin protein in their
stems and leaves giving the plants insect-resistance.
The toxic protein is specific to insect pests
(important) and harmless towards to animals, including humans and
other harmless insects - but the long-term effects of the
genetically modified genome are unknown.
This method, in principle, is good for farming
because it increases crop yield, less eaten by insects,
and reduces the use of insecticides - less harmful chemicals in
the environment e.g. using less
insecticides is less damaging to ecosystems in the countryside.
BUT, there is often a BUT!
As the insects feed on the crops they are
constantly exposed to the toxin, so that later generations of the
susceptible insects may develop resistance to the toxin and no
longer die from its effects - so farmers may have to use other
Also, although it kills the caterpillar or
larvae, that eat the crops, it only works on some orders of
insects e.g. moths and butterflies - the most serious pests
Farmers can use other insecticides - but
these are already being overused - one of the main reasons for the
decline of bee populations in many countries.
(When writing this, I found from the
internet, that toxin-resistant strains of insects are already
Development of 'Golden Rice' to increase nutritional value.
Increase the content of beta-carotene in golden rice, bananas
or other crops
to reduce vitamin A deficiency in humans.
A lack of vitamin A in the body can be fatal,
but a GM crop may help this reduce this deficiency in some people's
Beta-carotene is essential for our bodies to
make vitamin A.
Vitamin A deficiency is common in many Asian
and African countries and can cause blindness.
This is due to too little
beta-carotene or vitamin A in their diet e.g. there is too little in
their traditional rice crops, so in these areas there is a problem
of Vitamin A deficiency..
Golden rice is a GM rice whose genetic make-up
contains two genes from other organisms which enable this variety of rice to
produce sufficient quantities of beta-carotene.
With golden rice as part of their diet, the
risk of vitamin A deficiency is reduced and less people are likely to go
Example 4. Production of insect-resistant, herbicide-resistant
and 'climate/weather' resistant crops
Crops can be genetically engineered to grow
and survive in drought conditions - lack of water puts a big
constraint on the quality and quantity of crop yields.
You can modify the genetic make-up of plants
by inserting genes that help plants be more resistant to certain 'pests' e.g. fungal attack or
Weeds are a nuisance to a farmer, they use up
nutrients in the soil and compete with the crop of e.g. grain,
reducing the crop yield.
But, you can also make GM crops resistant to a
herbicide being used to kill all weeds in the field of growing crops i.e.
only the crop that you want survive and the weeds dies!
As the crop grows the field is sprayed with
herbicide, the crop is unaffected and the weeds killed.
This sounds good, BUT there is
considerable concern, with available scientific data to prove
it, about the use and effect of herbicides and insecticides on the
local ecology e.g. damage to wild flowers, and particularly insects
like important pollinating bees.
All of these effects will help to increase
the quality and yield of a crop - particularly important food
crops like maize, wheat and barley.
A gene that helps fish survive
in cold water has been inserted into the genome of a tomato plant to
help the plant survive in a colder climate i.e. the plant is able to
cope with lower temperatures than the original plant.
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