SNC2D – Tissues, Organs and Systems
Reading: Classical and Genetic Breeding of Crop Plants
(Source: Nova/Frontline: “Harvest of Fear)
Do you want to eat plants whose genes have been manipulated? If not, you should avoid eating produce!
Crop plant genes have been mixed and matched by farmers for thousands of years. Assyrian carvings
dating back to around 900 B.C. clearly depict the act of plant cross-pollination. Around the same time,
Central American farmers were selectively breeding a variety of crop plants, especially corn.
Classical Breeding:
For corn that is sweet, potatoes that are non-toxic -- all crop plants, in fact -- you have genetic
manipulation to thank. And selective breeding is really just a primitive form of genetic manipulation.
When a breeder chooses a male plant and a female plant for breeding, what he or she is really doing is
choosing specific genes to combine from those two plants. By hand-delivering pollen (sperm) from the
male plant to the female flower (which produces the egg), the breeder intervenes in the natural
fertilization process to ensure that traits from the two "best" plants get passed on to their offspring. It's
like an arranged marriage for plants.
But selective breeding is both imprecise and inefficient. Thousands of genes combine at once, and the
offspring plant may not receive the exact combination of genes the breeder had intended. The breeder has
no way of knowing whether the desirable genes are in the sperm and egg; one can only guess, based on
the parent plants' appearance. Many offspring may need to be produced in order to get one with the
desirable trait. So genetic manipulation through selective breeding is a slow process of trial and error.
Genetic Engineering:
Genetic engineering, however, is a targeted approach that allows scientists to remove specific genes from
one organism and insert them into another. The gene recipient is called a genetically modified organism,
or GMO (also called a "transgenic"). This efficient technique is also remarkable because it allows genes to
be transferred between different species, for example, between a flounder and a strawberry. Classical
breeding could never achieve such a thing, since it requires the parent organisms to be of the same species.
As genetic engineering techniques improve, more and more GMOs are being grown and put on grocery
store shelves. And while the GM food industry touts the benefits of genetic modification, ranging from
increased crop yields to enhanced nutritional content of GM foods, the public is not convinced. In fact,
despite the United Nations Development Programme's (UNDP) official support of GM foods, many
developing countries are opposed to growing or consuming them.
Research scientists are working on a wide range of transgenic modifications. The research may produce
plants that:
 Are resistant to pests, diseases and adverse growing conditions such as drought or frost
 Manufacture vaccines and other valuable medicines
 Have greater nutritional value
 Are able to absorb more carbon dioxide from the air
 Manufacture valuable biological materials such as spider web protein.
There are several varieties of crop plants (such as corn, soybeans, and canola) that have
been modified to make them resistant to certain herbicides. This allows the farmer to spray the entire field
with a chemical that will kill all the weeds but leave the crop plants unharmed.
SNC2D – Tissues, Organs and Systems
Opposition to GMOs
Public outcry stems from four main concerns. First, GMOs can interbreed with their non-GM
counterparts, moving the foreign genes into "wild" populations. This is especially true in plant
populations, since GMO pollen can easily be blown onto non-GM plants. Second, many believe GMOs
are unsafe, possibly causing allergic reactions, illness, and even death; however, these claims have not yet
been validated. Third, many have a visceral dislike for GMOs because they are just not "natural":
strawberries don't mate with flounder. Last but not least, in the U.S., many consumers are outraged
because foods containing GMOs are not currently labeled as such, so they can't be identified or avoided.
The GM food industry will have to quell the public's misgivings before the technology can be fully
implemented. But if the industry can demonstrate that GM foods are, indeed, ecologically harmless and
safe for consumers, GM foods may become a predominant part of our future diet.
Discussion Questions:
1. For what kind of characteristics have food crops been selectively bred?
2. What are 2 differences between classical breeding and genetic breeding of crop plants?
3. What arguments could be used in support of genetic breeding of plants?
4. What are 4 main concerns about the genetic breeding of crop plants?