Whether we realize it or not, genetic engineering has become a routine part of our lives. While debate over stem cell research rages in the United States, genetically modified organisms have quietly assumed an important place in generating industrial enzymes and new drugs. More than half of the land growing cotton, corn, and soybeans in the United States is now planted with genetically modified varieties. Gene therapy has not yet lived up to scientists' initial hopes, but it remains a promising treatment. The vanguard of the genetic revolution has arrived: how beneficial will genetic engineering prove?
John Avise, an evolutionary geneticist from the University of Georgia, acts as an amiable guide to the biotechnology revolution underway. In a series of vignettes he samples developments in genetically engineered microbes, crops, domesticated animals, and other organisms, concluding with a look at the history and promise of gene therapies for humans. Although each essay is only two to four pages long, Avise strives to provide sufficient detail to convey the challenges involved in engineering each organism or trait. Most biologists reading this book will find a mix of familiar case studies, such as genetically engineered insulin and Bt-corn, as well as less-known cases such as low-phosphorous pigs and zebrafish bio-sensors.
Avise boldly ends each essay with his personal assessment of the overall merit of the project to society, given in the form of a "boonmeter," which grades each case as a boondoggle, hype, hope, or boon. While we applaud his willingness to provide a summary judgment of each project, the boonmeter unfortunately confounds technical feasibility and likely societal benefits, which in some cases may provide a misleading view of a project's overall merit. For example, Avise rates both DNA vaccines and the cloning of endangered species as "hype." However, he views DNA vaccines as a potentially useful technology that faces some difficult technical hurdles, while perceiving cloning as a distracting and expensive diversion from more effective measures to conserve biodiversity, even if technical difficulties can be overcome. Avise's nuanced judgments might have been better summarized by separate gauges of technical feasibility and societal benefits.
Avise's discussion of the engineering of crops to produce more vitamins illustrates his skill in leading readers through the complexities of genetic engineering. Vitamin E, or tocopherol, comes in two forms, one of which is more readily retained and used by the body. Unfortunately, most crop sources of tocopherol contain 90% of the less-effective g-form. Studies in bacteria initially identified the gene, g-TMT, which converts g-tocopherol to a-tocopherol. This gene was later [End Page 150] identified in the mustard Arabidopsis, the plant equivalent of the lab mouse. If this gene could be made to produce more of its enzyme in seeds, the seeds should contain more of the usable form of vitamin E. A seed-specific promoter was known in carrots, so the g-TMT gene was attached to this promoter and then delivered to the mustard using a modified bacterium, Agrobaceterium, that normally causes infection in plants. The modified mustard plants produced nine times as much of the useful form of tocopherol, suggesting that this might be a feasible technology.
A second example illustrates the breadth of Avise's perspective in assessing the merit of genetically engineered organisms. The Roundup Ready soybean, engineered by Monsanto, includes Salmonella genes that block the action of glyphosphate, the active ingredient of Roundup. This technology allows farmers to avoid plowing for weed control, using Roundup instead, thus potentially reducing soil erosion. Further, using Roundup, a relatively benign herbicide due to its rapid breakdown, allows farmers to avoid using atrazine, a more persistent herbicide that may be linked to amphibian declines. However, Avise describes several problems that limit the potential benefits of this technology. First, the current strains of herbicide-tolerant soybeans show lower yields than their intolerant relatives, which may be due to inadequate attention to yield during breeding or may be a...