io9 | Over the past several decades, biologists have refined their transgenic techniques, including the introduction of DNA microinjection, embryonic stem cell-mediated gene transfer, and retrovirus-mediated gene transfer.
More recently, scientists have figured out how to modify the DNA of plants and animals to much greater degrees of precision. While techniques using bacterial and viral DNA enabled scientists to transport genes into the chromosomes of various organisms, the precise target for where the transgene was to eventually land could not be controlled. The CRISPR/Cas9 system, which normally allows the bacterial immune system to store DNA 'fingerprints' of viruses, now enables scientists to choose a specific region of the genome for either gene disruption (a gene knockout) or insertion (creating a more-precise transgenic organism).
This technology is extremely powerful because the original genes of an organism (its endogenous genes) provide a direct entryway for scientists to control, or edit, an organism's biology. For instance, if someone has a mutation that causes a disease in a particular type of cell, using CRISPR/Cas9 to replace the mutant gene with a normal gene could theoretically cure that disease. Likewise, it could be used to introduce a foreign transgene.
So, for example, scientists have used CRISPR/Cas9 to correct B-thalassemia (a condition similar to sickle-cell anemia) in human blood cell lines. They also used it to fix a mutation causing a liver disease in mice (though their technique only corrected 0.4% of mutated liver cells, these cells were able to rescue liver function). Additionally, researchers recently used the technique to create programmable antibiotics that selectively targets undesirable microbes.
Today, transgenic organisms are used for a number of purposes, from toxicology and the improvement of plants and livestock to the creation of animals that simulate human diseases. They can be divided into three major functions:
- To obtain information on gene function and regulation as well as on human diseases
- To obtain high value products (recombinant pharmaceutical proteins and xeno-organs and xeno-tissues for humans) to be used for human therapy
- To improve animal products for human consumption.
As noted by Emily Anthes , author of Frankenstein's Cat, genetically engineered animals could do real good for the world. As she notes in The New York Times, scientists have created transgenic salmon that can reach their adult size in a year and a half, rather than three years. There's also the famous "spider goats" — hybrid goats that secrete exceptionally strong strands of spider's silk, and transgenic glow-in-the-dark pigs and rabbits that use jellyfish DNA (the point of which kind of eludes me).