Download Biology 11.3 Genetic Engineering in Agriculture

Biology 11.3 Genetic Engineering in Agriculture
Genetic
Engineering in
Agriculture
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Improving Crops
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Farmers began primitive genetic
breeding years ago by selecting
seeds from their best plants,
replanting them, and gradually
improving the quality of their crops
over time.
Today, we use genetic engineering
to select and add characteristics
and modify plants by manipulating a
plant’s genes.
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Improving Crops
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Genetic engineering can change
plants in many ways; from making
plants drought resistant to making
plants that can thrive in different
soils, climates or environmental
conditions.
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Improving Crops
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Genetic engineers have developed
crop plants that are resistant to a
biodegradable weedkiller called
glyphosate. This enables farmers to
spray their fields with glyphosate,
kill all the weeds off, and leaves
the crops unharmed.
Half of the 72 million acres of
soybeans planted in the U.S. in
2000 were genetically modified to
resist glyphosate.
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Improving Crops
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Scientists have also developed
crops that are resistant to certain
insects by inserting specific genes
into plants.
This added gene makes the plants
produce proteins that make the
plant unacceptable to the insects
for a food source.
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More Nutritious Crops
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Genetic engineering has been able,
in many instances, to improve the
nutritional value of many crops.
For example, in Asia , rice is a
major food crop. Rice however is
low in iron and beta-carotene.
Genetic engineers have modified
rice in these countries by adding
genes which boost the levels of iron
and beta-carotene to the rice
plants.
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Risks of Modified Crops
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Risks: Many people, including many
scientists, have expressed concern
that genetically modified crops (GM
crops) might turn out to be
dangerous.
 What kind of unforeseen negative
affects might we experience from the
new engineered crops?
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Potential problems:
We have already noted that crops
such as soybeans have been
genetically altered to make them
resistant to the weedkiller
glyphosate.
Scientists are concerned that the
use of glyphosate will lead to weeds
that are immune to this weedkiller.
Than we will need to search for a
new weedkiller and alter more crops
to
be resistant to it.
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Risks of Modified Crops
Are GM crops harmful to the
environment?
 Will genes introduced into crops by
genetic engineering pass on to wild
varieties of plants?
 This type of gene flow happens all the
time between related plants.
 In most crops however, no closely related
wild version of the plant is nearby to take
up the gene changes.
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Some scientists fear that insect
pests may become immune (by
adapting) to the toxins that are
genetically engineered in some
plants.
 This would lead to insect strains that are
harder to kill as they would be immune to
the genetically produced changes that
were supposed to repel them.
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Gene technology in Farm Animals
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Farmers have, for generations,
improved their stock of animals
through selection of the best and
cross breeding.
Now, many farmers use geneticallyengineered techniques to improve
their stock or their production.
 Many farmers add growth hormone to
the diet of their cows to increase the
amount of milk their cows produce.
The cow growth hormone gene is
introduced into bacteria which is
than added to the cow’s food supply.
 This increases the amount of milk the
cow produces.
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Scientists have also boosted growth
in pigs by adding growth hormone
genes to the food that pigs eat.
These procedures lead to faster
growth and higher profits for
farmers.
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Making Medically Useful Proteins
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Another way in which gene
technology is used in animal farming
is in the addition of human genes to
the genes of farm animals to
produce human proteins in milk.
This is used for complex human
proteins that cannot be made by
bacteria through gene technology.
The human proteins are extracted
from the animal’s milk and sold for
pharmaceutical purposes. These
animals are called transgenic
animals because they have human
DNA in their cells.
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Making Medically Useful Proteins: Cloning
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More recently, scientists have
turned to cloning animals as a
way of creating identical animals
that can make medically useful
proteins.
In cloning, the intact nucleus of
an embryonic or fetal cell is
placed into a new egg whose
nucleus has been removed.
The egg with the new nucleus is
than placed into the uterus of a
surrogate mother and is allowed
to develop.
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Making Medically Useful Proteins: Cloning
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Cloning from Adult Animals:
In 1997, the first successful
cloning using differentiated cells
from an adult animal resulted in a
cloned sheep named Dolly.
A differentiated cell is a cell
that has become specialized to
become a specific type of cell.
In Dolly’s case; a lamb was cloned
from the nucleus of a mammary
cell taken from an adult sheep.
Scientists thought that a
differentiated cell would NOT
give rise to an entire animal. The
cloning of Dolly successfully
proved otherwise.
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Making Medically Useful Proteins: Cloning
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An electric shock was used to
fuse mammary cells from one
sheep with egg cells without
nuclei from another sheep.
The fused cells divided to form
embryos, which were implanted
into surrogate mothers. Only one
embryo survived the cloning
process.
Born July 5, 1996; Dolly was the
first cloned sheep, genetically
identical to the sheep that had
provided the mammary cell.
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Problems with Cloning:
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Since Dolly’s birth in 1996,
scientists have successfully
cloned several animals.
Only a few of these cloned
animals survive however. Many
become fatally oversized.
Others encounter problems in
development. For example, three
cloned calves were born in March
2001, only to die a month later
from immune system failure.
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The Importance of Genomic Imprinting
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Technical problems with
reproductive cloning lie within a
developmental process that
conditions egg and sperm so that
the “right combination of genes”
are turned “on” or “off” during
early stages of development.
When cloned offspring become
adults, a different combination
of genes is activated.
The process of conditioning the
DNA during an early stage of
development is called genomic
imprinting.
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The Importance of Genomic Imprinting
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In genomic imprinting, chemical
changes made to DNA prevent a
gene’s expression without
altering it’s sequence.
Usually, a gene is locked into the
“off” position by adding methyl
groups to it’s cytosine
nucleotides.
The bulky methyl groups prevent
polymerase enzymes from
reading the gene, so the gene
cannot be transcribed.
Later in development, the methyl
groups are removed and the gene
is reactivated.
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Why Cloning Fails:
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Normal vertebrae development
depends on precise genomic
imprinting.
This process, which takes place
in adult reproductive tissue,
takes months for sperm and
years for eggs.
Reproductive cloning fails
because the reconstituted egg
begins to divide within minutes.
There is simply not enough time
in these few minutes for the
reprogramming to process
properly.
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Why Cloning Fails:
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Gene keys fail to become
properly methylated, and this
leads to critical problems in
development.
Because of these technical
problems; and because of ethical
problems, efforts to clone
humans are illegal in most
countries.
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