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There are a few answers to this question, depending on what you're asking.
If you're asking if genes can individually "pop out" of a living thing and move to another one outside of reproduction, the answer is no. See Can DNA (from genetically engineered organisms) mutate me? for a more detailed answer, and also Can (genetically engineered) plants spread their genes to unrelated species? for a related hypothetical case. If you're asking about transmission of genes as part of reproduction, the answer depends on how far out you're asking the genes to go, in terms of genetic distance between the original host and the new one. For members of the same species, certainly. See Can (genetically engineered) plants spread their genes to wild relatives by cross-pollination?. Across species boundaries, hypothetically. See Can (genetically engineered) plants spread their genes to unrelated species?. Also see Can DNA (from genetically engineered organisms) mutate me?. See these topics in Life's Big Instruction Book: What's that? |
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Plants become weedy by acquiring traits we don't like, like spreading rapidly
or being difficult to eradicate. Since these traits are sometimes useful
to plants by giving them an advantage over other plants, they sometimes
occur as a result of natural selection. For example, Purple Loosestrife
is used as a garden plant in some parts of the United States,
but in other parts, it tends to sow seeds rapidly, and is therefore considered
a weed. Similarly, raspberry bushes have a bad habit of growing by underground
stems, and so are hard to get rid of in some places.
Presently, only one trait genetically engineered into plants can cause them to become weedy: resistance to a herbicide. (Plants also have been bred to resist herbicides via artificial selection, and they show the same trait.) So far, this trait has been added only to crop plants, which are unlikely to become weedy because they need a great deal of human help to grow. For more detailed answers, see:
What risks do plants
(genetically engineered) to resist herbicides pose to the environment?
See these topics in Life's Big Instruction Book:
What's that?
traits,
evolutionary advantage (fitness),
natural selection,
artificial selection,
genetic engineering
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| See What are the risks of genetic engineering? in the biotechnology FAQ. |
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There's really only two risks, but they are likely ones. First, herbicide-resistant
crop plants might cross-pollinate their wild relatives, which then
become weedy. Second, herbicides used poorly with herbicide-resistant
plants may lead to weeds becoming resistant to those herbicides.
See: Can (genetically engineered) plants spread their genes to wild relatives by cross-pollination?
See these topics in Life's Big Instruction Book: What's that? traits, evolutionary advantage (fitness), natural selection, artificial selection, genetic engineering |
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The answer depends on what question you're asking. If you're asking
about herbicide resistant plants spreading their own genes, see
Can (genetically engineered) plants
spread their genes to wild relatives by cross-pollination? for the answer.
If you're asking whether the use of herbicides along with herbicide-resistant plants will select for weeds that resist that herbicide, then this is a possible to likely risk, depending on the weeds, the herbicide in question, and how it's being used. Any species of plant can develop tolerance to any herbicide (or any other novel stress) via natural selection. It's more likely to do so if the stress isn't very severe (low doses of herbicide), and/or the same stress is applied for a long time (repeated use of the same herbicide over generations of plants). While it's certainly possible that plants will develop tolerance to any herbicide, it's also possible that the development of herbicide resistant crops -- both through genetic engineering and artificial selection -- may make it more likely. Presently, herbicide resistant crops have been developed to resist only a handful of herbicides. This may encourage farmers to repeatedly use only those herbicides, which may lead to weeds becoming resistant to them. (Some weeds started out resistant to them, and have never been affected.) On the other hand, those herbicides have been designed to be hard for plants to develop resistance to them. One thing that's unlikely to happen is the rise of "superweeds" -- weeds that resist many herbicides. Bacteria which gain resistance to many antibiotics -- some they've never been exposed to -- are sometimes called "superbugs". However, they gain resistance to many antibiotics through a process of genetic exchange called conjugation. No higher organisms engage in conjugation; they have to be exposed to stresses and evolve resistance to them through natural selection, a far slower process. Furthermore, unlike germs, which can only be attacked by poisons (since they're so small), weeds can always be cut down, dug up, or plowed under. See these topics in Life's Big Instruction Book: What's that? evolution natural selection, artificial selection, genetic engineering, bacteria (prokaryotes), higher organisms (eukaryotes), conjugation |
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Pesticide-making plants pose three risks to the environment. Two are old
risks, and one is new.
The old risks are the ones seen with overuse or misuse of any pesticide: evolution of pesticide-resistant insects and accidental killing of desirable insects. These risks occur regardless of the source of the pesticide, be it naturally occurring, "organic", synthetic, or genetically engineered. In fact, some insects are resistant to plants' own pesticides, so farmers need to rotate their crops, and try to predict whether resistant bugs will be prevalent in a given year. The one new risk is the possibility that genetically engineered plants will spread their genes for making pesticides to wild relatives, which may make the first two risks worse. Keep in mind that all plants, both wild and domestic, have been locked in an evolutionary arms race with insects that try to eat them since insects first emerged. All plants produce insecticides (to a greater or lesser extent). Some insects have evolved to cope with specific insecticides, and eat the plants that make them. People's deliberate use of pesticides has increased the selective pressure on insects to resist them, but this alone doesn't mean that they'll succeed in becoming resistant. For example, it's likely that some insect species evolved resistance to the bacterial pesticides generally known as Bt a very long time ago. Scientists first noticed this resistance in the early 1970s, long before plants were genetically engineered to produce Bt, and only soon after Bt became popular as an "organic" pesticide. Increasing use of Bt has slowly increased the proportion of insects resistant to it, first with Bt's use in "organic" farming, and now with its use in genetically engineered plants (corn and cotton most notably). If we continue to increase our use of Bt, and don't develop any other pesticides, it's likely that we'll see more and more Bt resistant insects. Conversely, if we maintain a large number of pesticides, and use them wisely, it's possible we may be able to hold down the proportions of insects that resist any or all of them. In any case, insects are not very likely to become as entirely resistant to as many pesticides as certain bacteria ("superbugs") have. Some bacteria are able to pass around genes in ways other living things don't -- this method is called conjugation. Other creatures must evolve resistance through natural selection, which is far slower, and far less certain to succeed. See these topics in Life's Big Instruction Book: What's that? evolution, selective pressure, natural selection, genetic engineering, conjugation Also see: What is Bt? |
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The answer depends on how closely related the two plants are. For detailed
answers, see:
Can (genetically engineered) crop plants
spread their genes to wild relatives by cross-pollination?
and also see:
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Certainly; it probably happens all the time where crop plants
are raised near their wild relatives. Fortunately, the wild relatives of
major crop plants aren't all that wide-spread. Corn's relatives occur only
in Mexico, and wheat's relatives are in Turkey.
Transferring genes from crop plants into their wild relatives is relatively harmless, with two significant exceptions: loss of diversity and development of weediness. Both of these share a common cause: a crop plant cross-pollinates a wild relative, and the offspring of the wild relative gain a useful trait. If the trait makes the offspring annoying to people, we may call them weeds; see How do plants become weedy. If the trait gives the offspring a large advantage over the rest of its species, they may be strongly selected for in their environment, and the other traits they had may spread rapidly through their species, possibly leading to the loss of other traits. This isn't a risk of just genetically engineered crop plants -- nearly all crop plants contain a least a few genes for traits useful in the wild, such as increased disease resistance or greater drought tolerance, for example. Of course, these genes aren't passed on in isolation, but are passed on with all the rest of parents' genes during reproduction.
It's also very likely that wild relatives have been cross pollinating
with domesticated crops for thousands of years, but we really don't
know if they have, or to what extent they have.
See these topics in Life's Big Instruction Book: What's that? sexual reproduction, natural selection, genes, traits, selective pressures, genetic diversity, an example of how selection can cause loss of genetic diversity |
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The answer depends on how closely related the species are. If the
species are closely related, it's likely. As the relationship becomes
more distant, the likelihood drops rapidly. Most crop plants have
only a few wild relatives, and they've become very distant from them
as a result of artificial selection.
Also see: Can (genetically engineered) crop plants spread their genes to wild relatives by cross-pollination? See these topics in Life's Big Instruction Book: What's that? |
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Not generally. The inability to pass genes between two different
species is generally what we mean when we say that they're unrelated
or distantly related.
Hypothetically, a retrovirus could move genes between unrelated species, but this would take a large number of unlikely things to all happen right. First, a retrovirus would have to pick up an entire gene from one living thing in addition to its own tiny genome (which is likely smaller than the gene, as genes in higher organisms contain introns), the retrovirus then has to evade the new organism's immune system, insert the gene into it (which may not happen, since the retrovirus generally doesn't have to worry about hitchhikers), and then the living thing has to be able to turn the gene on, by have activators that match its promoter. Scientists suspect this may have happened a few times over the billions of years living things have lived on Earth. Two things of note: first, all genes are alike to this process; it is no more or less likely to happen with an engineered gene than any other. Second, some bacteria can pass genes back and forth among themselves by a process called conjugation. They don't, however, spread their genes to other organisms that way. See these topics in Life's Big Instruction Book: What's that? species, sexual reproduction, retrovirus, DNA, genes, promoters, activators, conjugation |
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Like other higher organisms (eukaryotes), plants pass their genes on
to their offspring through sexual reproduction. Anything that
prevents reproduction -- something that makes them sterile -- will
prevent them from passing on any of their genes. Many plants
contain genes that prevent the male plant from producing
fertile pollen. These genes, called male sterility factors or
"terminator genes" render the male plants sterile. Since the main
concern with genetic spread is cross pollination by plants carrying
novel genes, this generally suffices.
As to whether sterile seed will have an effect on farming, see:
Will farmers become dependent
on seed companies?
See these topics in Life's Big Instruction Book: What's that? |
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Terminator genes (or male sterility factors) make male plants sterile. This prevents them from passing on their genes to their offspring via sexual reproduction. Male sterility factors have traditionally been used to develop and maintain some hybrid crops, most notably corn. Recently, seed companies have proposed using them with genetically engineered crops to ensure that the crops will produce sterile seed, or otherwise be unable to reproduce. Using male sterility factors this way prevents farmers from replanting seed, since none of it will be viable. However, few farmers replant seed anyway. See A Brief Introduction to Agribusiness for a more detailed answer. See these topics in Life's Big Instruction Book: What's that? |
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Bt is the common name for a class of insecticidal proteins made by
the bacterium Bacillus thuringiensis.
See these topics in Life's Big Instruction Book: What's that? |
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Bt has two main advantages over older synthetic pesticides: it's
very selective, and it breaks down quickly. Each of the different kinds
of Bt toxins kills only a few kinds of insects, so it doesn't kill
beneficial insects (such as bees and spiders) and certainly doesn't kill
other sorts of animals. By breaking down quickly, Bt doesn't build up
where it's used, which in turn does two things: it reduces the selective
pressure on resist insects, slowing their spread; and it further reduces
the possibility that it will affect other creatures.
While Bt has these advantages over older pesticides, newer pesticides are also selective and break down quickly. |
| Plants that make their own Bt provide three advantages to farmers. First, since the plants are always making it, they may stop infestations very early, before the farmer even knows insects are attacking his crops. Second, they eliminate the need to spray pesticides, which is difficult for certain tall crops, such as corn and sunflowers. Third, and most importantly, the Bt made by plants reaches insects that live inside the plant, where they're all but impossible to reach with other poisons. This is particularly advantageous for fighting off corn borers, which eat their way through corn stalks and ears of corn. |
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See these topics in Life's Big Instruction Book: What's that?
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