Gene Technologies
Chapter 13
Changing Genes?
• Some gene technologies involve
changing the genes of an individual.
• We’re going to look at some of the
science and consider some of the risks
and benefits of these technologies.
Harnessing Nature
• Gene-altering technologies often
harness the ability of certain microbes to
insert or alter genes of other organisms.
Bacteria already do “gene therapy” on one another.
(b) Transformation
with DNA fragment
bacterial
chromosome
(c) Transformation
with plasmid
bacterial
chromosome
DNA
fragments
DNA fragment is
incorporated into
chromosome.
plasmid
Plasmid replicates
in cytoplasm.
Viruses are expert at inserting their genes into
living hosts.
virus
viral DNA
2 Virus enters host cell.
host cell
3 Virus releases its DNA into host cell;
some viral DNA (red) may be incorporated
host cell
1 Virus attaches to
DNA
into the host cell’s DNA (blue).
susceptible host cell.
viral DNA
Viral proteins
“hybrid virus”
6 Host cell bursts,
releasing newly assembled viruses.
When “hybrid viruses” infect a
second cell, they may transfer
5 New viruses assemble;
genes from the first cell to the
host cell DNA is carried
second cell.
by “hybrid viruses.”
4 Viral genes encode synthesis
of viral proteins and viral gene
replication. Some host cell DNA
may attach to replicated viral
DNA (red/blue).
“Gene Gun”
• Another method of inserting genes into
cells is the biolistic particle deliver
system, or “gene gun.”
• The “gene gun” uses compressed air to
“shoot” microscopic particles coated with
DNA into cells.
“Gene gun” technology
Gene Therapy
• Gene therapy may provide ways to treat
single-gene genetic disorders.
• Gene therapy takes advantage of viruses
as vectors for inserting “good” genes into
cells that have “broken” genes.
• Ashanti deSilva was
one of the first people
to undergo gene
therapy.
• Ashi was born with
ADA deficiency. She is
missing an enzyme
critical for her immune
system.
• The enzyme was necessary for white blood cell function.
Researchers used a virus that parasitizes white blood
cells to insert a functional gene for the ADA enzyme
• The virus inserted the gene in Ashi’s white blood cells,
where it successfully produced the ADA enzyme
• White blood cells live
a few months, so Ashi
has to return for
frequent treatments. If
her bone marrow cells
could be treated, she
might be cured.
• With gene therapy,
Ashi lives a healthy,
productive life.
• The virus used in Ashi’s therapy is
known to cause cancer. What are the
risks and benefits of her treatment?
• Other children with ADA deficiency are
treated with enzyme therapy. This is a
less risky and less expensive, but less
effective treatment. How do the risks of
gene therapy balance against the
benefits?
• In a clinical trial of gene therapy to treat
cystic fibrosis, researchers inserted the
good CF gene into a cold virus.
Unfortunately the volunteer’s immune
system reacted against the virus to
strongly that the volunteer died. Given
this risk, do you think that this research
should continue? If not, why? If so, under
what conditions?
GMOs
• For thousands of years, farmers have been
changing the genetics of their crops through
selective breeding.
• Only recently have humans been able to
change the genetics of crops and livestock by
deliberately inserting new genes to make
Genetically Modified Organisms (GMOs).
DNA including Bt gene
Ti Plasmid
Cut both with the same restriction enzyme.
Genes are prepared for insertion into a DNA plasmid from
bacteria, which will be used to insert the gene into a plant
cell.
Mix Bt gene and plasmid; add DNA ligase to seal DNA.
The enzyme ligase is used to seal the trans gene into the
bacterial plasmid.
Transform Agrobacterium tumefaciens with recombinant
plasmid.
A. tumefaciens
bacterial
chromosome
plasmids
Plasmids are applied to a culture of bacteria that are known
to infect plant cells.
Infect plant cell with transgenic bacterium.
plant
chromosomes
A. tumefaciens
plant cell
The bacteria attacks a plant cell and attempts to insert its
own DNA. It inserts the trans plasmid instead.
plant
chromosomes
A. tumefaciens
plant cell
Insert Bt gene into plant chromosome.
Bt gene
If all goes well, the gene will be inserted into the plant’s
DNA and will be expressed in the plant.
Transgenic plant cells are treated with hormones to grow
new plants, and plants are tested for expression of the new
gene.
• Successful crops that have been
developed by genetic modification:
• herbicide-resistant crops
• crops that produce substances toxic to
insect pests but not to people
• bananas that contain vaccine proteins,
to vaccinate children in developing
nations against cholera
GMOs and ethics
• Producing GMO crops is expensive, and
companies expect return on their
investment. Companies patent the
genome of their crops to protect their
investment.
• Consider the following “worst case”
scenarios (based on actual events) and
the ethical issues involved.
• A farmer in Canada grows non-GMO corn.
He saves seed from each crop and plants it
the next year. Technicians from a large
corporation remove corn from his land
without his knowledge, test it, and find that
his corn has cross-pollinated with their
patented GMO corn, which another farmer
several miles away is growing. The
corporation sues the farmer for pirating their
crop. The farmer also loses his organic
status for producing corn that is genetically
modified.
• A large corporation develops a GMO rice
that has more protein and vitamins than
ordinary rice. They give some to rice
farmers in India. These farmers normally
save seeds each year and replant them.
After their first harvest, the corporation tells
the farmers that they must buy seeds next
year, because harvested seeds will be
sterile. The farmers protest. They say they
can’t make a living if they have to buy
seeds each year, and they should have
been told this to begin with.