When the FDA began considering the possibility of transgenic salmon as a food source recently, many Americans were left asking, "Trans-what?" With a bevy of terms like "genetically modified" (GM), "transgenic" and "heirloom" being slung around, it's becoming harder and harder to decipher what exactly we are eating. Here we take a closer look at how the DNA of our food — and our understanding of it — has changed over the years.
Discovering DNA: The power of peas
For as long as mankind has been growing crops or raising livestock, we've been tampering with the genes of our food. Before we knew what genes were, before we ever dreamed of DNA, farmers noticed that big, beautiful animals tend to make big, beautiful babies. They began selectively breeding for the traits that made the animals easy to work with, or that made them good producers of meat, milk and eggs. After generations of selective breeding, these animals were distinct from their ancestors and new breeds appeared. These outward changes (what scientists call the phenotype) reflect inward changes in the animal's genes (its genotype).
By the mid-nineteenth century, scientists were beginning to understand the basis of these heritable changes. Gregor Mendel famously showed how the traits of peas — traits like flower color and shell shape — passed from generation to generation. A few years later, a Swiss doctor named Friedrich Miescher isolated a substance from the nucleus of broken cells. He called this stringy goo "nuclein." Today, we call it DNA.
But it wasn't until the 1940s that the connection between Mendel and Miescher's work was finally made. Oswald Avery showed that nucleic acid (Miescher's nuclein) is the material which confers heritable traits (such as Mendel's wrinkly peas). Shortly after this discovery, the structure of DNA was solved and with that, the modern field of molecular genetics was born.
Today, we can manipulate molecules of DNA in a number of ways. We can copy them, cut them up, rearrange and reassemble them, we can transfer them from one organism to another, we can even make entirely artificial genes. By doing this, we not only change the genotype of an organism, we also change its phenotype. Instead of breeding tomatoes for many generations to achieve a certain trait, we can now simply insert the gene we want and — Voila! — in a single generation, we have heartier fruit.
How genes work: Before mash-ups, there were mixtapes
It may sound simple, but genetic modification is still a complicated process. Let's imagine that DNA is an old-fashioned mixtape. Each audio cassette holds a single long piece of tape which, in turn, holds a number of songs. The songs aren't necessarily related to one another; you might, for example, find some old-school Beastie Boys right next to Lady Gaga's latest. Also, each song has a little space on either side of it, a gap that lets the listener know that one song has ended and another is about to begin.
Like the tape, DNA is a single long, flexible string that contains a number of individual genes along its length. Each gene is like a song and, although adjacent genes aren't necessarily related, they do have stops and starts between them that let us know where one gene ends and another begins. Just as our mixtape would be a stringy mess if it wasn't wound onto the spools of the cassette, the DNA also needs to be organized. In most cases, it's wound up into bundles which we call chromosomes. So, in this analogy, the chromosome (the cassette) holds a long ribbon of DNA (the tape), which, in turn, contains a number of genes (songs) with stops and starts between them.
But how do we "hear" the songs? Just as a cassette player reads the magnetic signature of the songs on the audio tape, machinery within the cell reads the genes on the DNA. It's a multi-step process which begins with the genes being transcribed. This means that a new version of a gene is made. The new version consists of RNA, a sort of molecular cousin to DNA. The RNA copy is then translated into a protein. The protein makes its way through the cell to some final destination where it does a job that contributes to the organism's phenotype. For example, a protein might help tomatoes to ripen, or it might make cattle gain weight, or it might give your baby blue eyes. DNA encodes genes which define your genotype. These genes are also the blueprint for the proteins which make your phenotype.
Selective breeding: Belgian beefcakes (and, no, I don't mean you, Van Damme)
So now we (finally) get back to the question of genetically modified food. Some organisms are bred to be a certain way. Take, for example, Belgian Blue cattle. Some centuries ago, a cow was born with a naturally occurring mutation in its myostatin gene. This gene encodes a protein that keeps muscles in check, preventing them from growing abnormally. Cows with the mutation lack myostatin so their muscles overgrow, leading to huge beefy cows with incredibly lean meat. That's great news for farmers who have selectively bred Belgian Blues to maintain this mutation over the years. It's bad news for the cows, however. Belgian Blue calves often grow so large in the womb that they can't be birthed naturally and Caesarian sections are neccessary. This is a clear example of humans tampering with the genes of our food — the myostatin mutation was relatively rare until we began in-breeding the cows to maintain it, however, Belgian Blues are not considered a genetically modified food. This distinction is reserved for foods that have been altered using more modern techniques.
The first GMO: You say tomato, I say … Flavr Savr?
In 1994, the FDA granted approval for the first genetically modified food to be sold. The Flavr Savr tomato was designed to address the problems of those rock hard, tasteless lumps that pass for tomatoes in most modern grocery stores. Natural tomatoes become soft as they ripen and, because soft tomatoes don't ship or store well, growers tend to pick the fruit while still green and firm, then chemically ripen them later. Flavr Savr's makers, Calgene, believed that a protein called polygalacturonase was responsible for the way tomatoes become soft as they ripen, so they located the gene responsible for polygalacturonase, made an antisense (backward) copy of the gene, and put this copy back into the tomato. Because the cell's machinery can't read the antisense copy, the gene can't be transcribed or translated and no protein gets made. The hope was that Flavr Savr tomatoes, which produce very little polygalacturonase, could be allowed to ripen on the vine while still maintaining their firmness. Unfortunately, the tomato variety that Calgene started with wasn't very tasty and Flavr Savrs eventually flopped in the commercial marketplace.
The new transgenics: Fishy business
With Flavr Savrs, the gene introduced was a modified version of the tomato's own gene, but what happens when we introduce something totally different? This is the case with AquaBounty salmon, the fast-growing super-fish which have been in the news of late. These atlantic salmon are transgenic
, meaning that the genes of another species have been spliced into their genome. In this case, scientists took the gene for a growth hormone from chinook salmon, combined it with the regulatory elements of an antifreeze gene from another fish, the ocean pout, and put the whole construct into Atlantic salmon. The regulatory elements of the gene are like the gaps on the mixtape that tell the listener where one songs stops and the next starts, however, with genes these elements also do a little more.
Every gene has a direction in which it's meant to be read by the cell's machinery. The special region of DNA just before the start of the gene is called the promoter; it tells the machinery that it's reached the start of a gene, tells it when to start reading that gene, and also helps determine how many RNA copies of the gene the machinery should make. The bit of DNA that comes just after the gene tells the machinery that it has finished reading and that the RNA copy should end.
With normal salmon, the promoter that controls the growth gene tells the machinery to start transcribing the gene only during times of the year when food is naturally plentiful. Food is not an issue in most farm settings, but the promoter doesn't know this. It still waits for the bountiful months of spring and summer to roll around. In the case of the AquaBounty construct, the pout regulatory elements don't care what time of year it is. They tell the cell's machinery to start making RNA copies of the chinook gene year-round so the fish start growing earlier and faster than they would normally grow. They reach full size up to one year ahead of their natural cousins.
The attack of unkillable canolas
So what does this mean for consumers? Are genetically modified organisms (GMOs) really Franken-foods? Or is this just a faster, more efficient way of getting the traits we want, a more rapid version of what smart breeders have been doing for thousands of years? The answer, as with most complex issues, lies on a case by case basis. While most GMOs probably aren't a huge threat to human health, they can have devastating impacts on natural populations and ecosystems if they are allowed to escape into the wild. The same genetic alterations that make these organisms beneficial for industry, can allow them to out-compete their wild counterparts, essentially robbing natural populations of habitat and resources. Because of this, most transgenic animals must be sterilized.
Transgenic plants, however, have already escaped. This includes two varieties of herbicide-resistant canola which now grow along roadsides in North Dakota. Interestingly, each of the varieties was engineered to be resistant to a particular herbicide, but the two strains interbred in the wild and have produced a feral hybrid which now exhibits resistance to both herbicides.
Although herbicide resistance may not seem like a dire threat, imagine if these canola plants were to invade wheat or corn fields. They are resistant to two of the most common herbicides so they cannot be killed as traditional weeds would. They could soon take over fields, requiring the use of new poisons, adding to the load of chemicals already being dumped onto the land and carried into America's rivers and streams through run-off.
Bringing back diversity: Why do all cows look the same?
As we become more aware of the genetics of our food, many consumers are asking what alternatives are there? These days, traditional breeding programs have been largely replaced by factory farms which breed and grow only the most efficient animals. This means chickens with enormous breasts and fast-growing beef cows. There is little diversity in today's farms. According to the Sustainable Table
, 99 percent of the turkeys grown in the U.S. belong to a single breed, the Broad-Breasted White, while 96 percent of the vegetable varieties that were available in 1903 are now extinct. Heritage and heirloom breeders are trying to reverse this trend by reintroducing some of the plants and animals that our ancestors grew and ate. By supporting well-balanced breeds and adding genetic diversity, they hope to make healthier stock that are also tastier on our tables.
So how do you know what to choose at the grocery store? First, educate yourself about your food and know where it comes from. Heritage meat comes from traditionally bred animals, from varieties and breeds which have been around for centuries. Heirloom veggies come from similarly bred plants. Factory meat and eggs often come from animals that have been selectively bred for traits that help profits, but maybe aren't so good for the animal.
If something says that it's genetically modified, read the label and find out what exactly has been changed. Some genetically modified products are meant to help the environment by enabling farmers to use less pesticide; others are designed to spare dwindling wild populations. Read about the technology and ask yourself if the benefits outweigh the potential threats.
In the end, no one can say what's best to eat when it comes to the genetics of our food, because we still don't know the whole story. Use your head, keep up on what scientists are discovering and, whatever you choose, do your best to support sustainable resources. Hopefully, after reading this, the genetic jungle might be a little easier to navigate.
Peas: Haessly Photography/Flickr
Belgian Blues: FaceMePLS/Flickr
Canola field: sethschoen/Flickr