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That makes Human Nature, the upcoming CRISPR documentary executive produced by Dan Rather and directed by Adam Bolt, especially impressive. It's a fascinating primer about what led to the discovery of the tool, and an exploration of the role it may have in our society. It's hopeful about CRISPR's ability to help us fix diseases that have plagued humans for millennia, while also questioning if we're ready to make genetic changes that'll affect us for generations to come.

CRISPR stands for "clustered regularly interspaced short palindromic repeats," referring to a unique series of gene sequences in DNA that are remnants of previous viral infections. Typically, cells would use that information to defend against those same viruses in the future. But scientists also discovered you can train enzymes called CRISPR associated proteins (or Cas, for short) to target specific pieces of DNA, snip them out, and replace them with whatever genetic code they want. CRISPR is like the cursor in a word processor, one scientist points out in the documentary, allowing you to easily jump edit aspects of your DNA.

"Scientists and the elite have known for a while about CRISPR and the vista that stretches ahead," said Dan Rather on stage at the film's SXSW premiere. "What I wanted was a film that would get the public involved in a conversation ... To use the Texas term, I wanted a film that would 'put it down where the calves would get it.'"

Director Adam Bolt, together with his co-writer Regina Sobel, manage to ground the wild story of CRISPR with a healthy dose of humanity. Early on in the film, we're introduced to David Sanchez, a teenager living with sickle cell disease, a genetic disease that prevents his blood cells from delivering enough oxygen to vital organs. The CDC estimates that around 100,000 people in the US currently have sickle cell, which predominantly affects people with ancestry from sub-Saharan Africa.

Even with modern treatment, which mostly amounts to constant blood transfusions, people affected by the disease typically don't live beyond their mid-40s. But now, we might finally have a way to fix the single mutation that causes sickle cell. In January, the FDA announced it would fast-track the approval of CTX001, an experimental therapy that uses CRISPR. If we finally have the ability to treat something that so many people are suffering from, why wouldn't we explore it?

Well, for one, once we start exploring gene editing, we have to deal with the ethical dilemmas of designer babies. Last year in China, Dr. He Jiankui made headlines when he claimed he used CRISPR to make a set of twin babies immune to HIV. Since then, researchers have said the treatment may have also impacted the infants' brains. Do we even have the right to explore this sort of germline gene therapy, which will be something generations ahead will inherit with untold consequences?

"Humans have done horrible things, but we're also capable of amazing things, and maybe that's something we can remember."

Human Nature wrestles with these concepts from just about every angle. Some scientists find germline editing completely unconscionable. While others, like Alta Charo, a bioethicist at the University of Wisconsin, think gene editing is a tool like any other, something that could be used for good or evil. It's not inherently bad on its own.

"Humans have done horrible things, but we're also capable of amazing things, and maybe that's something we can remember," Bolt said. "[The film is] something that tells us maybe we're capable of harnessing this very powerful technology if we work together."

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CRISPR doc 'Human Nature' embraces the hope and peril of gene editing

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That makes Human Nature, the upcoming CRISPR documentary executive produced by Dan Rather and directed by Adam Bolt, especially impressive. It's a fascinating primer about what led to the discovery of the tool, and an exploration of the role it may have in our society.

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De-extinction Article Questions

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Earth is in the midst of its sixth mass extinction: Somewhere between 30 and 159 species disappear every day, thanks largely to humans, and more than 300 types of mammals, birds, reptiles, and amphibians have vanished since 1500. These rates do not bode well for the future of life on our planet, but what if extinction wasn't permanent? What if we could resurrect some of the species we've lost?

For decades the notion of "de-extinction" hovered on the scientific fringes, but new advances in genetic engineering, especially the CRISPR-Cas9 revolution, have researchers believing that it's time to start thinking seriously about which animals we might be able to bring back, and which ones would do the most good for the ecosystems they left behind. Indeed, earlier this month, ecologists at the University of California, Santa Barbara (UCSB), published guidelines for how to choose which species to revive if we want to do the most good for our planet's ecosystems.

The two animals at the forefront of this discussion are the woolly mammoth, a hairy, close relative of the elephant that lived in the Arctic, and the passenger pigeon, a small, gray bird with a pinkish red breast once extremely common in North America. The last mammoths died about 4000 years ago, and the passenger pigeon vanished around 1900. Research on reviving both species is well underway, and scientists close to the field think de-extinction for these animals is now a matter of "when," not "if."

With that prospect in mind, here's what we know so far about de-extinction:
Why bring back extinct animals?
As cool as it might be to visit a zoo filled with woolly mammoths, saber-toothed tigers, and giant tortoises, the best reasons for bringing back extinct animals have more to do with ecology than tourism. "If this is always going to be a zoo animal, then stop," says ecologist Ben Novak, the lead researcher on the passenger pigeon project at Revive & Restore-a foundation devoted to genetically rescuing endangered and extinct species in San Francisco, California. "The goals have to be about ecological restoration and function."

Every animal in an ecosystem has a function: Bats eat insects, fish clean algae from coral, grazers spread nutrient-rich dung across habitats. Some functions are redundant -shared among multiple different animals-but others are fulfilled by just one or two species.

Both the passenger pigeon and woolly mammoth were functionally unique species, and when they went extinct, their habitats changed dramatically. Harvard University's George Church, the lead researcher working to de-extinct the mammoth, says that bringing back the giants could help convert the Arctic tundra back to grasslands that existed during the last ice age. He points to research that shows that mammoths and other large herbivores trampling across the ancient Arctic ecosystems helped maintain the grasslands by knocking down trees and spreading grass seeds in the dung. When the large herbivores disappeared, the ecosystem transitioned to today's mossy tundra and taiga that is beginning to melt and release carbon dioxide into the atmosphere. Reviving the mammoth, Church says, could help slow climate change by shifting the landscape back toward the grasslands. "There's twice as much carbon at risk in the tundra than in all the forests of the world put together."

Likewise, the passenger pigeons, whose numbers are estimated to have reached nearly 5 billion at the start of the 19th century, played a dramatic role in shaping the forests they inhabited. Their numbers were so great and their droppings so prevalent and flammable that they destroyed trees and increased forest fires. After their extinction, these healthy natural disturbances ceased, white oaks lost their primary mode of seed dispersal (i.e., via bird droppings), and the forests have never been the same. "The passenger pigeon is a very important ecological species for the habitat that we want to restore," Novak says.

How do you de-extinct an animal?
There are three main approaches to de-extinction scientists talk about. The first, called backbreeding, involves finding living species that have traits similar to the extinct species. Then scientists would selectively breed these animals to try to make a version that more closely resembles the extinct animal- a process already underway for some extinct species like aurochs. This isn't really a true de-extinction, but it might still let us fill in missing ecological functions. In the case of mammoths, scientists might try to mate Asian elephants with more body hair than usual, for example.

A second option is cloning. Scientists would take a preserved cell from a recently extinct animal (ideally before the last of its kind died) and extract the nucleus. They would then swap this nucleus into an egg cell from the animal's closest living relative and implant the egg into a surrogate host. (Researchers actually did this in 2007, and a common goat gave birth to an extinct species, the Pyrenean ibex. The infant lived only 7 minutes however, because of genetic problems with its lungs.) Cloning may eventually give us basically identical genetic copies of extinct species, but we'll be restricted to animals that went extinct more recently and have well-preserved cells with intact nuclei. The mammoth and the passenger pigeon may never be cloned.

The newest option is genetic engineering. Here, researchers would line up the genome of an extinct animal with that of its closest living relative. They would then use CRISPR and other gene-editing tools to swap relevant genes from the extinct animal into the living species and implant the hybrid genome into a surrogate (or grow it in an artificial womb). This approach doesn't produce genetically identical copies of extinct animals, but rather modern versions of an animal engineered to look and behave like its extinct relatives. This is the technology being used by the mammoth and passenger pigeon groups.
How close are we?
That depends on what you count as a true de-extinction, which is sort of a gray area. If scientists engineer an Asian elephant to have small ears, extra fur, and more body fat by swapping in mammoth DNA, is it still an Asian elephant?

"If you're willing to accept something that is an elephant that has a few mammoth genes inserted into its genome and therefore is able to make some proteins that mammoths might, we're probably closer to that," says Beth Shapiro, author of How to Clone a Mammoth: The Science of De-Extinction and an evolutionary biologist at UC Santa Cruz specializing in ancient DNA.

The passenger pigeons project faces similar questions. Novak wants to resurrect the bird using its closest living relative, the band-tailed pigeon, but how many genes need to be swapped to constitute success is somewhat arbitrary. "The two genomes are 97% the same. That 3% has built up over many millions of years and the majority of it is noise," he says. "So the actual differences are much likely a smaller portion-probably within the realm of several thousand mutations. What we want to find is the key 20 or 100 mutations that affect the traits that are most important."

There's also a divide as to what constitutes a de-extinction success for the scientists versus the public. Genetically coaxing to behave like their extinct relatives might restore the ecosystem's lost function, Novak says. But is that good enough to count? "I don't think anyone in the world is really going to call it de-extinction unless the bird looks right."

Even if researchers can pinpoint and transfer those key mutations (a daunting task), DNA is only half the battle. From there it's a matter of getting the hybrid cell to grow in a surrogate, hoping all the genes work harmoniously together, bringing the hybrid to term, and hoping it acts like the extinct species even though it was raised by a modern relative. If all that goes right, you still need the hybrids to mate and give birth to fertile offspring. "I think the hardest part is getting developmental biology to go," says Philip Seddon, a conservation biologist at the University of Otago, Dunedin, in New Zealand and the lead author on a recent report by the International Union for Conservation of Nature (IUCN) that issued guidelines for de-extinction research.

It's a monumental task, but Novak says that if his team can secure enough funding, "there's no reason that we can't have the first generations of passenger pigeons by something like 2022 to 2025. Everyone running these projects would very much like to be in 10-year time frames."

How do we choose which animals to de-extinct?
In their recent publication, Douglas McCauley, an ecologist at UCSB, and his colleagues argue for three criteria to consider when choosing de-extinction candidates: Select target species with unique functions, concentrate on species that went extinct recently, and only work with species that can be restored to levels of abundance that meaningfully restore ecological function.

Although the mammoth and the passenger pigeon might pass McCauley's first criterion, experts are skeptical about whether they're truly the best animals to focus on. Shapiro points out that ecosystems are not static and have continued to change since these animals went extinct. "I worry about the dramatic changes to the forest in the eastern part of the North American continent," she says. "I think there's a lot we need to understand better about the passenger pigeon's ecology and the effect that the passenger pigeon would have on that habitat before we can make a sufficiently educated decision."

McCauley has similar worries: "Forests have fragmented, forests have expanded and contracted. A passenger pigeon that hits that forest again is going to be like a middle-aged guy who really wants to go back to high school and then he gets back there and he's like, 'Whoa I don't fit in anymore.'"

He thinks that de-extinction efforts should instead be focused on recently extinct animals like the Christmas Island pipistrelle bat ( Pipistrellus murrayi), the Réunion giant tortoise ( Cylindraspis indica), and the lesser stick-nest rat ( Leporillus apicalis). Although not as charismatic as a woolly mammoth, he says these creatures still have habitats to return to and would restore a unique function in their ecosystems. The lesser stick-nest rat, for instance, did what its name implies and built large stick nests in central Australia that became hubs of biodiversity.
What are the risks?
The spread of genes can be difficult to control. We probably won't lose track of mammoths in Siberia, but what about rats? "It becomes hard to control those sorts of populations," Seddon says. "And there are the same fears one might have about genetically modified crops-the idea that a modification may move into relatives, may jump in and out, or may not be expressed in the way that you expect." Scientists are confident that there's a safe way to proceed, but mistakes may come at a high cost if we can't put the genie back into the bottle if something goes wrong. "If we lose sight of the true gravity of extinction and overzealously embrace de-extinction as a mitigation tool, it would be really easy to manufacture forests, savannas, and oceans full of Franken-species and Eco-zombies," McCauley says.

But in spite of any danger, McCauley says his biggest concern isn't a runaway genetic experiment wreaking havoc on a fragile ecosystem. "Honestly, the thing that scares me most is that the public absorbs the misimpression that extinction is no longer scary," he says. "That the mindset becomes: Deforest, no biggie, we can reforest. If we drive something extinct, no biggie, we can de-extinct it."

Introducing (or reintroducing) a new species to a habitat always comes with some risk, but de-extinction scientists point out that we've been able to manage that risk successfully with living animals like reintroducing wolves into Yellowstone National Park or beavers into the United Kingdom. There have also been disasters, like the poisonous cane toad in Australia, which was originally imported to help control the gray-backed cane beetles that were damaging sugar crops, but is now spreading across the continent and depleting native populations.

"De-extinction is just the next step in a progression that conservation has already been on," Novak says. "If you want to restore the ecological function of an extinct species, and you don't have any living species that will do that, you take the closest living species you can get and adapt it based on the genome of the extinct species."

IUCN has been dealing with these sorts of issues for years now, and so stands uniquely poised to help regulate de-extinction science's future. Still, there are no laws requiring that researchers take its advice. The only legal structures governing de-extinction are borrowed from genetically modified organism and cloning research-fields regulated by the U.S. Food and Drug Administration, Department of Agriculture, and Environmental Protection Agency.

Regardless, de-extinction is speeding closer to reality, and now is the time to start thinking about it, McCauley says. "For a long time it was easy to just put it aside because the technology wasn't there," he says. "But I don't think we can do that anymore."

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Should we bring extinct species back from the dead?

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Earth is in the midst of its sixth mass extinction: Somewhere between 30 and 159 species disappear every day, thanks largely to humans, and more than 300 types of mammals, birds, reptiles, and amphibians have vanished since 1500. These rates do not bode well for the future of life on our planet, but what if extinction wasn't permanent?

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Genetically Modified Mosquitoes | HHMI BioInteractive Video

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Learn the process by which a line of genetically modified mosquitoes was engineered to reduce populations of Aedes aegypti mosquitoes in the wild. Viruses like Dengue, chickungunya, yellow fever, and Zika virus are spread by a species of mosquitoes called Aedes aegypti. To reduce the number of infections, health officials use various methods aimed at reducing mosquito populations.

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A female Aedes aegypti mosquito, a carrier of the Zika virus, feeds on human blood.

Credit: CDC/James Gathany

With Zika virus on the rise in parts of South and Central America, experts are seeking new ways to curb the spread of the potentially dangerous virus.

The Zika virus can cause an infection with mild symptoms, but experts are concerned that infections in pregnant women may lead to a condition called microcephaly in their children. Microcephaly affects the brain and severely impacts a child's cognitive development. On Feb. 1, the World Health Organization announced that microcephaly possibly linked to the Zika virus constitutes a public health emergency.

Although not yet developed, a vaccine has the potential to offer widespread protection against the virus for people who come into contact with it. But another possible means of preventing the spread of Zika is to target the mosquito that carries the virus, in hopes of preventing bites - and exposure to the virus - in the first place. One way of doing this would be to use insecticides to eliminate the mosquitoes; however, another technique that is gaining popularity is the use of genetically modified mosquitoes. [ Zika Virus FAQs: Top Questions Answered]

By manipulating certain genes in the mosquitoes, scientists can cause the population to crash (or, in other words, die off), said Anthony James, a professor of microbiology and molecular genetics at the University of California, Irvine.

This is the genetic equivalent of an insecticide, James told Live Science.

There are several ways to do this. One option is to insert a lethal gene into the sperm of male mosquitoes that causes their offspring to die before they reach adulthood, James said. Another option is to manipulate the genes in the females so that they can't fly - and therefore don't find mates - and leave no offspring, he said.

Aside from these "population suppression" approaches, scientists are also looking into a method called "population replacement." Using population replacement, scientists would tweak a gene in order to reduce the mosquito's ability to transmit a pathogen, he said.

This technique has been tested in mosquitoes that carry the parasite that causes malaria, James said. However, it's a less popular idea in the fight against a flavivirus such as the Zika virus, because rather than targeting just one flavivirus, a researcher would want to target all of them, which would require sufficient engineering, he said. Other flaviviruses carried by mosquitoes include dengue, yellow fever and chikungunya.

Indeed, with the Zika virus, the population-suppression technique is simpler, James said. By eliminating the mosquitoes that carry flaviviruses, rates of all of these diseases would drop, he said.

Currently, one British company called Oxitec has a strain of Aedes aegypti mosquitoes (one of the species that carry flaviviruses) that can be used to suppress the population using males that carry a lethal gene.

The mosquitoes were designed to reduce the spread of the dengue virus, but because the same mosquitoes carry Zika, they could work for the Zika virus as well, James said.

Field trials of these mosquitoes are currently taking place in Brazil, according to the company.

One potential downside to population suppression is that it could affect "nontarget" populations. In other words, researchers consider whether killing off a population will affect others in the area - for example, those that rely on that species for food.

But this isn't a worry with Aedes aegypti mosquitoes, James said. "It's important to emphasize that [ A. aegypti] are an invasive species" in the Western Hemisphere, James said. That means that they are not a natural part of the ecosystem, and eliminating them could potentially have positive effects, as opposed to harming the ecosystem, he said.

There are also concerns about what would happen if the manipulated gene were transferred to another species. One way to avoid this is to manipulate the genes in the male mosquitoes, which do not bite and therefore wouldn't come into contact with other species, James said.

Follow Sara G. Miller on Twitter @SaraGMiller. Follow Live Science @livescience, Facebook & Google+. Originally published on Live Science.

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Zika Prevention: The Buzz on Genetically Modified Mosquitoes

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With Zika virus on the rise in parts of South and Central America, experts are seeking new ways to curb the spread of the potentially dangerous virus. The Zika virus can cause an infection with mild symptoms, but experts are concerned that infections in pregnant women may lead to a condition called microcephaly in their children.

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by P. Byrne* (8/14)

Quick Facts...

Genetic modification (GM) technology allows the transfer of genes for specific traits between species using laboratory techniques.

GM crops were first introduced in the U.S. in the mid-1990s. Most current GM crops grown in the U.S. are engineered for insect resistance or herbicide tolerance. Corn, soybeans, and cotton are the three largest acreage GM crops.

GM crops grown in Colorado include corn, alfalfa, sugar beet, soybeans, and canola.

Potential future applications of the technology include nutritional enhancements, stress tolerance, disease resistance, biofuel efficiency, and remediation of polluted sites.

GM crops are regulated at the federal level by the U.S. Department of Agriculture (USDA), the Environmental Protection Agency (EPA) and the Food and Drug Administration (FDA), each with authority to oversee specific aspects of the crops and their products.

Since GM crops were introduced in the U.S. in the mid-1990s, they have become widely adopted by growers of several largeacreage field crops. This fact sheet explains the technology for developing GM crops and describes GM crops currently on the market in the U.S.

What are GM crops?

The term genetically modified (GM), as it is commonly used, refers to the transfer of genes between organisms using a series of laboratory techniques for cloning genes, splicing DNA segments together, and inserting genes into cells. Collectively, these techniques are known as recombinant DNA technology. Other terms used for GM plants or foods derived from them are genetically modified organism (GMO), genetically engineered (GE), bioengineered, and transgenic. 'Genetically modified' is an imprecise term and a potentially confusing one, in that virtually everything we eat has been modified genetically through domestication from wild species and many generations of selection by humans for desirable traits. The term is used here because it is the one most widely used to indicate the use of recombinant DNA technology. According to USDA standards for organic agriculture, seeds or other substances derived through GM technology are not allowed in organic production.

Which GM crops are currently grown in the U.S.?

Although in the U.S. genetically engineered versions of 19 plant species have been approved, only eight GM crop species are grown commercially (Figure 1). Because several of them are major crops, the area planted to GM varieties is very large. Most current GM crops have been engineered for resistance to insects, tolerance to herbicides (weed control products) or both.

Figure 1. Currently grown GM crops in the U.S., traits for which they are modified, and percent of total acreage of the crop that is planted to GM varieties. IR=insect resistant, HT=herbicide tolerant, DT=drought tolerant, VR=virus resistant.

What traits have been modified in GM crops?

Insect-resistant crops contain genes from the soil bacterium Bacillus thuringiensis (Bt). The protein produced in the plant by the Bt gene is toxic to a targeted group of insects-for example European corn borer or corn rootworm-but not to mammals. The most common herbicide tolerant (HT) crops are known as Roundup Ready®, meaning they are tolerant to glyphosate (the active ingredient in Roundup® herbicide). Glyphosate inactivates a key enzyme involved in amino acid synthesis that is present in all green plants; therefore, it is an effective broad spectrum herbicide against nearly all weeds. Roundup Ready® crops have been engineered to produce a resistant form of the enzyme, so they remain healthy even after being sprayed with glyphosate. Some cultivars of corn and cotton are referred to as 'stacked', meaning they have transgenes for both insect resistance and HT. According to USDA-ERS (2013), over half of the U.S. corn and cotton acreage was planted to stacked cultivars in 2013.

Which GM crops are grown in Colorado?

Corn, alfalfa, and sugar beet are the major GM crops grown in Colorado, but smaller areas of soybeans and canola are also planted. The corn, alfalfa, and soybean crops are nearly all used as livestock feed. Sugar beet is used to extract and purify sugar, and canola is used mostly for edible oil. All GM seeds are targeted to commercial growers; no vegetable or fruit varieties for home production are GM.

What are potential GM crops of the future?

Some potential applications of GM crop technology are:

Nutritional enhancement: Higher vitamin content; more healthful fatty acid profiles;

Stress tolerance: Tolerance to high and low temperatures, salinity, and drought;

Disease resistance: For example, orange trees resistant to citrus greening disease or American chestnut trees resistant to fungal blight;

Biofuels: Plants with altered cell wall composition for more efficient conversion to ethanol;

Phytoremediation: Plants that extract and concentrate contaminants like heavy metals from polluted sites.

How are GM crops regulated in the U.S.?

Three U.S. government entities have authority to regulate GM crops: the United States Department of Agriculture (USDA), the Environmental Protection Agency (EPA), and the Food and Drug Administration (FDA). They do not, however, individually regulate all GM crops. For example, USDA is involved in approving the field release of most GM plants, but EPA is involved only in pest and pesticide resistance traits, and FDA only regulates crops destined for food, feed, or pharmaceuticals. Thus, EPA does not have authority to regulate a vitamin-enhanced tomato, and FDA would not regulate a drought tolerant turfgrass. These federal agencies review extensive information submitted by the crop developer, for example, the nature and stability of the transgene and its protein product, effects on non-target organisms in the field environment, composition of the food product, and potential for allergic reaction. If the agencies are satisfied that the proposed crop does not pose threats to the environment and does not increase risks for food or feed safety, the crop is determined to have nonregulated status, that is, it is approved for commercialization.

Are GM crops grown in other countries?

According to a recent report (James 2014), GM crops were grown in 26 other countries in 2013. The largest global acreage crops were soybean, corn, cotton, and canola, in that order. The U.S. has the greatest area of these crops, about 40% of the world total. Other large producers include Brazil, Argentina, India, and Canada.

Besides GM crops, are there other GM ingredients in our food supply?

No GM food animals have yet been approved in the U.S., although a GM salmon engineered for rapid growth is under review. GM microorganisms are used to produce rennin for production of cheese and GM yeast has been approved for winemaking .

How does GM technology differ from other plant breeding techniques?

The era of scientific crop improvement dates back to around 1900, when the impact of Gregor Mendel's studies on trait inheritance in peas became widely recognized. Since then, a broad range of techniques has been developed to improve crop yields, quality, and resistance to disease, insects, and environmental stress. Most plant breeding programs rely on manual cross-pollination between genetically distinct plants to create new combinations of genes. The progeny plants are intensively evaluated over several generations and the best ones are selected for potential release as new varieties. An example is a tomato variety that is selected for disease resistance and tolerance to cool temperatures. Other techniques included within the conventional plant breeding toolbox are development of hybrid varieties by crossing two parental strains to produce offspring with increased vigor; and induced mutations to create useful variation. GM technology is much more precise in that it transfers only the desired gene or genes to the recipient plant. Another branch of agricultural biotechnology-distinct from GM technology-involves selecting plants for DNA patterns known to be associated with favorable traits such as higher yield or disease resistance.

The shared DNA code

Most organisms store their genetic information in the form of DNA molecules in chromosomes. The sequence of chemical bases in a DNA strand encodes a specific order of amino acids, which are the building blocks of proteins. Proteins carry out many functions in cells and tissues, which together are responsible for an organism's characteristics. Because most life forms share this same language of heredity-and due to scientific advances in molecular biology-it is now possible to transfer a gene from one species to another, for example from a bacterium to a plant, and have it function in its new host.

What is inserted into a GM plant?

The inserted DNA fragment contains one or a few genes, which contain the DNA sequence information encoding specific proteins, along with DNA segments that regulate production of the proteins. The inserted fragment also sometimes contains a marker gene to easily identify plants that have incorporated the transferred genes, also known as transgenes, into their chromosomes.

How are transgenes inserted?

There are two principal methods for transgene insertion:

Gene gun: In this method, microscopic pellets of gold or tungsten are coated with the transgene fragment and shot at high velocity into plant cells or tissues. In a small proportion of cases, the pellet will pass through the cells and the DNA fragment will remain behind and become incorporated into a plant chromosome in the cell nucleus.

Agrobacterium tumefaciens: This method utilizes a biological vector, the soil dwelling bacterium Agrobacterium tumefaciens, which in nature transfers part of its DNA into plants and causes crown gall disease. Genetic engineers have taken advantage of this DNA transfer mechanism while disarming the disease-causing properties. Plant and bacterial cells are co-cultivated in a petri dish under conditions that facilitate gene transfer. This allows incorporation of genes in a more controlled manner than with the gene gun; however, it does not work equally well in all plant species.

How are whole plants obtained from plant cells or tissues?

Insertion of transgenes is generally an inefficient process, with only a few percent of plant cells or tissues successfully integrating the foreign gene. Various strategies are used to identify the small percentage of cells/tissues that have actually been transformed. The next step is to develop those cells or tissues into whole plants capable of producing seed. This is done through a process called tissue culture, that is, growing plants on agar or a similar medium in the presence of plant nutrients and hormones under controlled environmental conditions.

What happens next?

The crop developers then begin a long series of evaluations to determine that the gene has been incorporated successfully, that it is inherited in a stable and predictable manner, that the desired trait is expressed to the expected level, and that the plant does not show any negative effects. Evaluations are initially done in controlled greenhouses and growth chambers. Once sufficient seed is produced and the appropriate permission is received, experimental plants are grown in field trials. Field evaluations follow strict guidelines that include isolation from related plants to avoid cross-pollination, careful cleaning of planting and harvesting machinery, frequent monitoring of crop growth, and checking the field for two seasons after the trial for the presence of volunteer plants that have arisen from seed inadvertently left behind.

References

Council for Agricultural Science and Technology (CAST). 2014. The potential impacts of mandatory labeling for genetically engineered food in the United States. Issue Paper 54. CAST, Ames, Iowa. Available at www.castscience.org/file.cfm/media/products/digitalproducts/CAST_Issue_Paper_54_web_optimized_29B2AB16AD687.pdf

Federoff, N. 2004. Mendel in the Kitchen: A Scientist's View of Genetically Modified Food. National Academies Press, Washington, D.C. Available at www.nap.edu/catalog.php?record_id=11000

James, C. 2014. ISAAA Brief 46-2013, Global Status of Commercialized Biotech/GM Crops: 2013. www.isaaa.org/resources/publications/briefs/46/default.asp

Kole, C., C.H. Michler, A.G. Abbott, and T.C. Hall. 2010. Transgenic Crop Plants. Vol. 1: Principles and Development. Springer-Verlag, Berlin, Heidelberg.

U.S. Department of Agriculture-Economic Research Service. 2013. Recent trends in GE adoption. www.ers.usda.gov/data-products/adoption-of-genetically-engineered-crops-in-the-us/recent-trends
*P. Byrne, Colorado State University, professor, soil and crop sciences. 8/14 Colorado State University, U.S. Department of Agriculture, and Colorado counties cooperating. CSU Extension programs are available to all without discrimination. No endorsement of products mentioned is intended nor is criticism implied of products not mentioned.
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Genetically Modified (GM) Crops: Techniques and Applications - 0.710 - Extension

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Since GM crops were introduced in the U.S. in the mid-1990s, they have become widely adopted by growers of several largeacreage field crops. This fact sheet explains the technology for developing GM crops and describes GM crops currently on the market in the U.S.

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The student will understand that biotechnology is the manipulation of living organisms to suit human purposes and that the impacts can be beneficial when precautions are taken and processes are scientifically evaluated.

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What Are Pathogens? | Health | Biology | FuseSchool

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Practice quiz for Probability of Inheritance

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How Mendel's pea plants helped us understand genetics - Hortensia Jiménez Díaz