Gene TechnologiesChapter 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.

(b) Transformationwith DNA fragment

(c) Transformationwith plasmid

bacterialchromosome

DNAfragments

bacterialchromosome

plasmid

DNA fragment isincorporated intochromosome.

Plasmid replicatesin cytoplasm.

Bacteria already do “gene therapy” on one another.

host cellDNA

Viral proteins

viral DNA

virus

host cell

“hybrid virus”

viral DNA

1 Virus attaches tosusceptible host cell.

2 Virus enters host cell.

3 Virus releases its DNA into host cell;some viral DNA (red) may be incorporatedinto the host cell’s DNA (blue).

4 Viral genes encode synthesisof viral proteins and viral genereplication. Some host cell DNAmay attach to replicated viralDNA (red/blue).

6 Host cell bursts,releasing newly assembled viruses.When “hybrid viruses” infect asecond cell, they may transfergenes from the first cell to thesecond cell.

5 New viruses assemble;host cell DNA is carriedby “hybrid viruses.”

Viruses are expert at inserting their genes into living hosts.

“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).

Cut both with the same restriction enzyme.

DNA including Bt gene Ti Plasmid

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 recombinantplasmid.

A. tumefaciens

bacterialchromosome plasmids

Plasmids are applied to a culture of bacteria that are known to infect plant cells.

Infect plant cell with transgenic bacterium.

A. tumefaciens

plant cell

plantchromosomes

The bacteria attacks a plant cell and attempts to insert its own DNA. It inserts the trans plasmid

instead.

Insert Bt gene into plant chromosome.

Bt gene

A. tumefaciens

plant cell

plantchromosomes

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

• 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.

GMOs and ethics

• 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.