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Biology: Chapter 11 Review Genetic Engineering
Gene
Technology
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The process of manipulating genes
for practical purposes is called
genetic engineering.
Genetic engineering may involve
building recombinant DNA; DNA
made from two or more different
organisms.
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Today, the human insulin gene is
transferred to bacteria through
genetic engineering.
Because the code is universal,
bacteria can transcribe and
translate a human insulin gene
using the same code a human cell
uses in order to produce human
insulin.
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Restrictive enzymes are bacterial
enzymes that recognize and bind to
specific short sequences of DNA, and
than cut the DNA between specific
nucleotides.
The DNA from a vector is also cut. A
vector is an agent that is used to carry
the gene of interest into another cell.
Plasmids are circular DNA molecules
that can replicate independently of the
main chromosomes of the bacteria.
The DNA fragments from the
organism containing the gene of
interest are combined with the DNA
fragments from the vectors.
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In our example, the DNA fragments are
combined with plasmid DNA fragments.
We develop a hybrid plasmid made of
both parts.
The host cells than take up the
recombinant DNA, this plasmid hybrid.
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In a process called gene cloning, many
copies of the gene of interest are made
each time the host cell reproduces. By
fission.
Cells that have received the particular
gene of interest are separated from
cells that did not take up the vector with
the gene of interest.
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The Human Genome Project is a research
project linking 20 labs in six countries.
Teams of scientists in the project worked
to identify and map all 3.2 billion base
pairs of all the DNA that makes up the
human genome.
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Exons are scattered about the human
genome in clumps that are not spread out
evenly among the chromosomes.
On most human chromosomes, great
stretches of untranscribed DNA fill the
chromosomes between the scattered
clusters of transcribed genes. These
untranscribed areas are like blank
recording tape.
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Human cells contain about 30,000 to 40,000 genes. This is only
about double the number of genes in a fruit fly.
It is only about one quarter of the 120,000 genes scientists had
expected to find.
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Drugs: Many genetic disorders and human illnesses occur when
the body fails to make critical proteins.
Today, many genetically engineered medicines are used to
treat everything from burns to diabetes.
Examples include: Erythropoetin for anemia, Growth
factors for treating burns, ulcers, Human Growth
Hormone for growth defects, Insulin for diabetes,
Interferons for viral infections and cancer, Taxol for
ovarian cancer
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Many viral diseases, such as smallpox and polio, cannot be treated by existing drugs.
Instead, they are combated by prevention through use of vaccines.
.
A vaccine is a solution containing all or part of a harmless version of a pathogen
(disease-causing microorganism).
•It is a weakened version of the disease; incapable of causing serious harm.
When a vaccine is injected, the immune system reads the pathogen and
responds by making defensive proteins called antibodies. The immune system
creates a defense system against this form of the disease.
•In the future, if the same pathogen enters the body, the antibodies are now
there to combat the pathogen and stop it’s growth before it can cause a
disease. The immune system stays in place so when the flu or cold strikes in full
force, the antibodies are already there to fight it before it can grow.
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With these types of vaccines there is always some small danger for getting
sick
as some people are more sensitive to the vaccine. Their threshold is low.
.
Vaccines made by genetic engineering avoid this danger and are less likely to
risk infection to those who are extra-sensitive to the microbes.
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Dna Fingerprinting:
•Other than identical twins, no two individuals have the same genetic
material.
•Scientists use DNA sequencing technology to determine a DNA fragment’s
nucleotide sequence.
•Because the places a restrictive enzyme can cut depend on the DNA
sequence, the lengths of the DNA fragments will vary between any two
individuals.
•A DNA fingerprint is a pattern of dark bands on photographic film that is
made when an individuals DNA restriction fragments are exposed to an Xray film.
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Today, we use genetic engineering to select and add
characteristics and modify plants by manipulating a plant’s
genes.
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.
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.
Scientists have also developed crops that are resistant to certain
insects by inserting specific genes into plants.
Genetic engineering has been able, in many instances, to improve
the nutritional value of many 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.
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.
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Are GM crops harmful to the environment?
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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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Farmers 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 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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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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More recently, scientists have turned to cloning animals as a way of
creating identical animals that can make medically useful proteins.
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In cloning, the intact nucleus of an embryonic or fetal cell is placed
into a new egg whose nucleus has been removed.
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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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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.
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.
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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.
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
The process of conditioning the DNA during an early stage of
development is called genomic imprinting.
In genomic imprinting, chemical changes made to DNA prevent a
gene’s expression without altering it’s sequence.
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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.
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.
Because of these technical problems; and because of ethical
problems, efforts to clone humans are illegal in most countries.
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