Biology 11.3 Genetic Engineering in Agriculture - Sleeping Dog ...


14 Δεκ 2012 (πριν από 9 χρόνια και 2 μήνες)

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Biology 11.3 Genetic Engineering in Agriculture

Engineering in

Improving Crops

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.

Improving Crops

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

Improving Crops

Genetic engineers have developed
crop plants that are resistant to a
biodegradable weedkiller called
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.

Improving Crops

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.

More Nutritious Crops

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

Genetic engineers have modified
rice in these countries by adding
genes which boost the levels of iron
and beta
carotene to the rice

Risks of Modified Crops

Many people, including many
scientists, have expressed concern
that genetically modified crops (GM
crops) might turn out to be

What kind of unforeseen negative
affects might we experience from the
new engineered crops?

Potential problems:

We have already noted that crops
such as soybeans have been
genetically altered to make them
resistant to the weedkiller

Scientists are concerned that the
use of glyphosate will lead to weeds
that are

to this weedkiller.
Than we will need to search for a
new weedkiller and alter more crops
to be resistant to it.

Risks of Modified Crops

re GM crops harmful to the


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


In most crops however,
no closely related
wild version

of the plant is nearby to take
up the gene changes.

Some scientists fear that insect
pests may become immune (by
adapting) to the toxins that are
genetically engineered in some

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.

Gene technology in Farm Animals

armers have, for generations,
improved their stock of animals
through selection of the best and
cross breeding.

Now, many farmers use genetically
engineered techniques to improve
their stock or their production.

Many farmers add
growth hormone
the diet of their cows to increase the
amount of milk their cows produce.
The cow growth hormone gene is
introduced into

which is
than added to the cow’s food supply.

This increases the amount of milk the
cow produces.

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

Making Medically Useful Proteins

Another way in which gene
technology is used in animal farming
is in the
addition of human genes
genes of farm animals
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.
animals are called

because they have human
DNA in their cells.

Making Medically Useful Proteins: Cloning

More recently, scientists have
turned to cloning animals as a
way of creating identical animals
that can make medically useful


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.

Making Medically Useful Proteins: Cloning

Cloning from Adult Animals:

In 1997, the
first successful

using differentiated cells
from an adult animal resulted in a
cloned sheep named Dolly.

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.
cloning of Dolly successfully
proved otherwise.

Making Medically Useful Proteins: Cloning

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

Born July 5, 1996; Dolly was the
first cloned sheep, genetically
identical to the sheep that had
provided the mammary cell.

Problems with Cloning:

Since Dolly’s birth in 1996,
scientists have successfully
cloned several animals.

Only a few of these cloned
animals survive however.
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.

The Importance of Genomic Imprinting

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

The Importance of Genomic Imprinting

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

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.

Why Cloning Fails:

Normal vertebrae development
depends on precise genomic

This process, which takes place
in adult reproductive tissue,

for sperm and

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

Why Cloning Fails:

Gene keys fail to become
properly methylated, and this
leads to critical problems in

Because of these technical
problems; and because of ethical
problems, efforts to clone
humans are illegal in most