You can't cross-breed a tomato with a fish. Genetic engineering involves snipping out a dna fragment from one organism (such as a fish) and inserting it into the dna of another organism (such as a tomato plant).
The famous "Doomsday Clock" lists genetic engineering as one of the ways we might do ourselves in:
http://www.thebulletin.org/content/doomsday-clock/overviewThe Doomsday Clock conveys how close humanity is to catastrophic destruction--the figurative midnight--and monitors the means humankind could use to obliterate itself. First and foremost, these include nuclear weapons, but they also encompass climate-changing technologies and new developments in the life sciences that could inflict irrevocable harm.
The Sierra Club describes the difference between cross-breeding and genetic engineering in layman's terms:
http://www.sierraclub.org/policy/conservation/biotech.aspxThe following policies on Biotechnology have been adopted by the Sierra Club Board of Directors:
GENETIC ENGINEERING is a new technology which, unlike traditional breeding methods, allows the transfer of genetic material from one organism into a host organism of an unrelated species, thus bypassing the natural reproductive barriers between species. The genetic manipulation resulting from genes inserted by genetic engineering cannot be recalled; the altered characteristics will be passed on to future generations and continue to be reproduced in the environment.
Genetic engineering became possible with the advent of recombinant DNA technology, which for the first time allowed for the transfer, using laboratory procedures, of DNA from one species into the DNA of an unrelated species. For purposes of this policy, however, we define genetic engineering to include all direct molecular manipulation of the genetic structure of organisms or viruses, including additions of foreign genes (transgenes), gene alterations, duplications, or deletions.
Genetic engineering is not, as many of its supporters claim, merely a more efficient form of traditional plant and animal breeding. There is a clear boundary between traditional breeding methods and the radically new technology of genetic engineering.
A GENETICALLY ENGINEERED ORGANISM (GEO) is a single-celled or multicellular organism, the genetic structure of which has been altered by genetic engineering, resulting in genetic changes that could not be achieved using conventional breeding methods. (The terms "GEO," "genetically modified organism" and "genetically altered organism" all have the same meaning.)
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Wikipedia has a long article describing the controversy over GM food:
http://en.wikipedia.org/wiki/GM_food_controversyThe Union of Concerned Scientists has a number of articles on genetic engineering at
http://www.ucsusa.org/food_and_agriculture/science_and_impacts/impacts_genetic_engineering/impacts-of-genetic.html