Depth study GMO and Transgenic organisms Flashcards
GMO vs transgenic organism
GMO: an organism that has acquired one or more genes by artificial means, or its genes have been artificially altered
Transgenic: a subset of GMOs, transgenic organisms are organisms that contain foreign genes from other species
Ti plasmids
- A plasmid from the agrobacterium tumefaciens bacterium
- T DNA, a section of the Ti plasmid, can be inserted into a plant host to transfer diseases to the host
- Scientists can create recombinant Ti plasmids to introduce desired characteristics into the cells of host plants, e.g. to make the plant herbicide resistant.
Utilitarian ethics in bioethics
- An ethical activity is one that provides the greatest balance of good over harm for society and the environment
- Ethicality is determined by outcome
Restriction endonuclease
A special restriction enzyme which cuts a specific point in a sequence of nucleotides to separate target DNA. The same restriction endonuclease is used for the target DNA and plasmid so the same “sticky ends” mean they join evenly in annealing. After ligase are added, this is now recombinant DNA.
NOTE: endonucleases is an umbrella term under which restriction enzymes are categorised. Endonucleases can cut the DNA anywhere, but restriction enzymes are more specific
Recombinant DNA in Transgenic Species
Added to bacterial vectors to create transgenic species
1. Restriction enzymes
2. Combines by annealing (matching sticky ends join) and sealing enzymes (DNA ligase) are used
Annealing process
to recombine DNA in the double stranded form - used to join together plasmid introduced DNA with hydrogen bonds.
Transgenes
Recombinant DNA/Plasmids that contain genetic material of different species
DNA recombination process
- Required gene is isolated from a cell
- A plasmid is removed from a bacteria
- The plasmid and the DNA containing the gene are both cut using the same restriction enzyme, producing fragments that having matching sticky ends (sections of single-stradned DNA with exposed nucleotide bases at the end of a double-stranded molecule)
- Annealing: the sticky ends of the human gene and the plasmid join up via base pairing
- Ligation: the DNA fragments are joined by DNA ligase, which seals and strengthens the onds
- The recombinant plasmid is inserted back into a bacterial cell, where multiple copies of the gene can be produced
- When multiple copies of the gene have been produced, the gene can be inserted into an egg cell of another species and, after fertilisation, it will become part of the newly formed organism’s DNA
Methods of delivering desired gene into a species
Micro-injection
- DNA is directly introduced in the nucleus of a single cell, usually an egg cell, using a fine-tipped glass needle
- E.g. human antithrombin gene microinjected into goat embryo’s nucleus
Biolistics
- A ‘gene gun’ ‘fires’ DNA into target tissues and cells on microscopic particles
- Tiny gold particles are used to coat the DNA, which is fired at the target cells under high pressure or voltage
Electroporation
- An electrical current is applied to the cell membrane to increase its permeability
Transduction
- DNA is carried into cells by a viral vector like adenovirus, liposome, or a bacterial plasmid. The vectors may be directly injected into the bloodstream, or delievered by aerosol (nasal spray or oral aerosol)
Uses in gene therapy
- A healthy copy of a gene can be inserted into defective somatic tissue in a mature organism
- Because the gene is not introduced into germline tissue, the healthy gene will not be passed down to offspring
- This is in contrast to transgenic organisms, where the new gene is introduced into a fertilised egg cell or germline cell, making the gene part of germline DNA so it can be passed down to subsequent generations
Example: Bt cotton plants
Caterpillar Helicoverpa zea moth destroys crops and is developing resistance to pesticides (natural selection!!)
- It is transgenic (gene from soil bacterium bt), and GM as its DNA is modified with biotechnology.
- With Bt cotton, spraying of pesticides is reduced → better for envrionment (less runoff, harmful chemicals) reducing pesticide resistant animals, less costly. The pesticides used are now narrow spectrum → beneficial insects are not killed, just mites and sucking insects.
Bt gene produces an inactive toxic protein - harmless to humans, most animals and insects. But when digested by a caterpillar, the digestive system converts it into an active form that causes death. Produced by:
- Calluses: small pieces of cotton seedlings + solid growth medium.
- Cotton plant embryos: More mature (6 weeks) callus cells + liquid medium + hormones
- Bt gene cut from bacterium’s genome (restriction enzymes!)
- Bt gene transferred to the cotton plant embryos using a vector (often agrobacterium tumefaciens)
- Bt gene containing embryos grown in a tissue culture and germinated into small plants. Glasshouses, then planted.
Refuge crops
Non-GMO crops planted alongside GMO crops like Bt cotton. Planted to generate a population of moths that are susceptible to the Bt toxin.
If there was no refuge crop, majority of caterpillars that survived feeding on the cotton crop would be resistant to the transgenic cotton. Although initially there would be very little caterpillars that survived due to toxic leaves, over time mutations could occur and resistance develop. If this population continued to interbreed, this could produce double resistant caterpillars - this would confer threatening resistance.
This is to support a population of moths to dilute the population of moths with a recessive allele. These moths continue to interbreed, to reduce to chances of interbreeding caterpillars with double recessive alleles.
Alfafa plant
- Transgenically modified to produce high levels of the amino acid cysteine, which produce higher quality of wool from sheep that graze it
- Also glyphosate-resistant alfalfa strains have been produced
Transgenic species and genetic diversity
Genes are moved from one species to another, greatly increasing genetic diversity as it would take thousands of years of evolution to introduce these traits, if ever. However, these genetically modified populations have very little genetic diversity. Being engineered, these is a small genetic base from which the population develops from. Additionally, as GMOs are often to improve efficiency, the genome might be regulated to be the most efficient - no variation.
Can also confer resistance on species that were previously susceptible to disease, allowing them to pass on their favourable genes.
Original genetic material might be reduced or lost forever → loss of biodiversity.
