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Transgenic Organisms
Transgenic organisms are genetically engineered to carry transgenes—genes from a different species—as part of their genome. The transgene may either b…
Scientists can genetically engineer organisms by transferring a gene of interest, such as the Bt toxin gene from Bacillus thuringiensis, into another organism, such as cotton. This allows the recipient organism to produce the Bt toxin protein, which protects the plant against specific insect pests.
The organism from which the gene of interest is taken is called the donor organism, and the organism that receives the gene is called the transgenic organism. The inserted gene is called a transgene.
For example, transgenic goats have been genetically engineered to produce spider silk proteins in their milk. These proteins can then be purified and processed into exceptionally strong fibers.
Scientists usually introduce these transgenes at the earliest stage of development, such as the fertilized egg stage.
This allows the transgene to become part of many cells in the organism, including the germ cells.
When the transgene becomes part of the germ cells, it can pass to future generations through breeding.
This creates a genetically modified line that can pass the transgene to its offspring.
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Q1: What is a transgene and how does it differ from an organism's native genes?
A transgene is a foreign gene, typically from another species, inserted into an organism's genome to produce a desired protein. Unlike native genes, transgenes are artificially introduced through genetic engineering techniques like recombinant DNA and DNA cloning. For example, transgenic goats produce spider silk in their milk by expressing an inserted transgene that doesn't naturally occur in goats.
Q2: Why is a transgene introduced at the fertilized egg stage in animals?
Introducing the transgene at the fertilized egg stage ensures it integrates into germ cells, the reproductive precursor cells that become gametes. This germline integration allows the transgene to be present in all developing cells and be inherited through breeding, creating stable lines of transgenic organisms that pass the foreign gene to offspring.
Q3: What methods are used to introduce transgenes into plant cells?
Plants commonly use biological methods, particularly bacterial vector delivery. Rhizobium radiobacter, a soil bacterium, naturally infects plants and integrates its plasmid DNA into the plant genome. Scientists modify this bacterium to carry transgenes, then culture plant tissue samples with the bacterium to allow infection and transgene integration into the plant's genome.
Q4: How do scientists identify cells that have successfully integrated a transgene?
Scientists include selectable markers, such as antibiotic resistance genes, or reporter genes like GFP alongside the gene of interest. These markers allow researchers to identify and select cells where the transgene has successfully integrated into the genome. Cells without successful integration lack these markers and can be eliminated during selection.
Q5: What are the main practical applications of transgenic organisms?
Transgenic organisms have diverse applications across agriculture, medicine, and industry. Transgenic plants provide insect resistance to reduce pesticide use; bacteria produce biofuels and human proteins for medicine; and transgenic animals serve as models for human disease research and manufacture therapeutic proteins, advancing both scientific understanding and practical solutions.
Q6: What is the difference between stable and transient transgene expression?
Stable transgene expression occurs when the transgene integrates into the organism's genome, allowing permanent, heritable expression across generations. Transient expression happens when the transgene remains in the cell but doesn't integrate, resulting in temporary protein production that isn't passed to offspring or maintained long-term.
Q7: How do scientists create homozygous transgenic animal lines?
Scientists use backcrossing, a process where transgenic offspring are mated with their parent to concentrate the transgene. Repeated backcrossing produces lines where both copies of the target gene carry the transgene, creating homozygous transgenic animals that consistently express the desired trait across all offspring.