Environmental Engineering Reference
In-Depth Information
1600
Terrestrial
organisms
1200
Marine
organisms
800
400
0
3500
545
500
440
410
355
290
250
205
145
65
1.8
0
Millions of years ago
Figure 4-10
Natural capital:
changes in the earth's biodiversity over geological time. The biological diversity
of life on land and in the oceans has increased dramatically over the last 3.5 billion years, especially during the
past 250 million years. During the last 1.8 million years this increase has leveled off.
Critical thinking: will the
human species be a major factor in decreasing the earth's biodiversity over this century?
Compared to traditional crossbreeding, gene
splicing takes about half as much time to develop a
new crop or animal variety and costs less. Traditional
crossbreeding involves mixing the genes of similar
types of organisms through breeding. Genetic engi-
neering, by contrast, allows us to transfer traits be-
tween different types of organisms.
Scientists have used gene splicing to develop
modified crop plants, genetically engineered drugs,
pest-resistant plants, and animals that grow rapidly
(Figure 4-12, p. 76). They have also created genetically
engineered bacteria to clean up spills of oil and other
toxic pollutants.
Genetic engineers have also learned how to pro-
duce a
clone,
or genetically identical version, of an in-
dividual in a population. Scientists have made clones
of domestic animals such as sheep and cows and may
someday be able to clone humans—a possibility that
excites some people and horrifies others.
Bioengineers have developed many beneficial
GMOs: chickens that lay low-cholesterol eggs, toma-
toes with genes that can help prevent some types of
cancer, and bananas and potatoes that contain oral
vaccines to treat certain viral diseases in developing
countries where needles and refrigeration are not
available.
Researchers envision using genetically engineered
animals to act as biofactories for producing drugs, vac-
cines, antibodies, hormones, industrial chemicals such
as plastics and detergents, and human body organs.
This new field is called
biopharming.
For example, cows
may be able to produce insulin for treating diabetes,
perhaps more cheaply than making the insulin in labo-
ratories. Have you considered this field as a career
choice?
4-5 WHAT IS THE FUTURE
OF EVOLUTION?
Artificial Selection and Genetic Engineering
We have learned how to selectively breed
members of populations and to use genetic
engineering to produce plants and animals with
certain genetic traits.
We have used
artificial selection
to change the ge-
netic characteristics of populations of a species. In
this process, we select one or more desirable genetic
traits in the population of a plant or animal, such as a
type of wheat, fruit, or dog. Then we use
selective
breeding
to end up with populations of the species
containing large numbers of individuals with the de-
sired traits.
Artificial selection has yielded food crops with
higher yields, cows that give more milk, trees that
grow faster, and many different types of dogs and cats.
But traditional crossbreeding is a slow process. Also, it
can combine traits only from species that are close to
one another genetically.
Today's scientists are using genetic engineering to
speed up our ability to manipulate genes.
Genetic en-
gineering,
or
gene splicing,
is a set of techniques for
isolating, modifying, multiplying, and recombining
genes from different organisms. It enables scientists to
transfer genes between different species that would
never interbreed in nature. For example, genes from a
fish species can be put into a tomato or strawberry.
The resulting organisms are called
genetically
modified organisms (GMOs)
or
transgenic organ-
isms.
Figure 4-11 outlines the steps involved in devel-
oping a genetically modified plant.
