Learning outcomes:
1 I can describe new technologies for recombining genetic material.
2 I can describe the use of biotechnology in various fields
4.2 Selecting Desirable Traits
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Artificial Selection is the process of selecting and breeding
individuals with desirable traits to produce
offspring with the desired traits.
The selection process is simple. Only those
individuals, with the desired trait, will be allowed
to reproduce.
This selection process also applies to plants,
which can be bred to possess desirable traits.
The main difference between 'natural' selection
and 'artificial' selection is that, the artificial selection process
is controlled by humans.
The process of intervention to
produce more desirable
organisms has been going on for
some time. This process takes a long
time to see results - usually many
generations. Farmers, dog and horse
breeders, along with scientists can
now speed up the artificial selection
process by using 'low-tech' or 'hightech' technologies, such as;
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cloning (made from cells)
artificial insemination
(artificially joining the male
and female gametes)
in vitro fertilization (male
and female gametes are
selected and then allowed to
fertilize in a controlled setting)
genetic engineering (directly
altering the DNA of an
organis
m)
Beneficial or detrimental to society? That is
one of the pressing questions that many
humans are struggling with, when it comes to
biotechnology. There are many good things that
can be produced, but what about the problems,
including,
risks in animals (reducing genetic
variation within a specific population, less
resistance to disease, birth defects and
other abnormalities)
risks in plants (resistance to herbicides)
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Using the information below, create a concept map (Web) of Biotechnology. If
you are unsure what a concept map is, go to page 497 of your text book. The
map to the top of the page may resemble your concept map.
What is Genetic Engineering?
Genetic engineering is a laboratory technique used by scientists to change the DNA of
living organisms.
DNA is the blueprint for the individuality of an organism. The organism relies upon the
information stored in its DNA for the management of every biochemical process. The
life, growth and unique features of the organism depend on its DNA. The segments of
DNA which have been associated with specific features or functions of an organism are
called genes.
Molecular biologists have discovered many enzymes which change the structure of DNA
in living organisms. Some of these enzymes can cut and join strands of DNA. Using such
enzymes, scientists learned to cut specific genes from DNA and to build customized
DNA using these genes. They also learned about vectors, strands of DNA such as
viruses, which can infect a cell and insert themselves into its DNA.
With this knowledge, scientists started to build vectors which incorporated genes of their
choosing and used the new vectors to insert these genes into the DNA of living
organisms. Genetic engineers believe they can improve the foods we eat by doing this.
For example, tomatoes are sensitive to frost. This shortens their growing season. Fish, on
the other hand, survive in very cold water. Scientists identified a particular gene which
enables a flounder to resist cold and used the technology of genetic engineering to insert
this 'anti-freeze' gene into a tomato. This makes it possible to extend the growing season
of the tomato.
At first glance, this might look exciting to some people. Deeper consideration reveals
serious dangers.
What are the Dangers?
Fundamental Weaknesses of the Concept
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Imprecise Technology—A genetic engineer moves genes from one organism to
another. A gene can be cut precisely from the DNA of an organism, but the
insertion into the DNA of the target organism is basically random. As a
consequence, there is a risk that it may disrupt the functioning of other genes
essential to the life of that organism. (Bergelson 1998)
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Side Effects—Genetic engineering is like performing heart surgery with a shovel.
Scientists do not yet understand living systems completely enough to perform
DNA surgery without creating mutations which could be harmful to the
environment and our health. They are experimenting with very delicate, yet
powerful forces of nature, without full knowledge of the repercussions.
(Washington Times 1997, The Village Voice 1998)
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Widespread Crop Failure—Genetic engineers intend to profit by patenting
genetically engineered seeds. This means that, when a farmer plants genetically
engineered seeds, all the seeds have identical genetic structure. As a result, if a
fungus, a virus, or a pest develops which can attack this particular crop, there
could be widespread crop failure. (Robinson 1996)
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Threatens Our Entire Food Supply—Insects, birds, and wind can carry
genetically altered seeds into neighboring fields and beyond. Pollen from
transgenic plants can cross-pollinate with genetically natural crops and wild
relatives. All crops, organic and non-organic, are vulnerable to contamination
from cross-pollinatation. (Emberlin et al 1999)
What is cloning? Are there different types of cloning?
When the media report on cloning in the news, they are usually talking about only one
type called reproductive cloning. There are different types of cloning however, and
cloning technologies can be used for other purposes besides producing the genetic twin of
another organism. A basic understanding of the different types of cloning is key to taking
an informed stance on current public policy issues and making the best possible personal
decisions. The following three types of cloning technologies will be discussed: (1)
recombinant DNA technology or DNA cloning, (2) reproductive cloning, and (3)
therapeutic cloning.
What are the risks of cloning?
Reproductive cloning is expensive and highly inefficient. More than 90% of cloning
attempts fail to produce viable offspring. More than 100 nuclear transfer procedures
could be required to produce one viable clone. In addition to low success rates, cloned
animals tend to have more compromised immune function and higher rates of infection,
tumor growth, and other disorders. Japanese studies have shown that cloned mice live in
poor health and die early. About a third of the cloned calves born alive have died young,
and many of them were abnormally large. Many cloned animals have not lived long
enough to generate good data about how clones age. Appearing healthy at a young age
unfortunately is not a good indicator of long-term survival. Clones have been known to
die mysteriously. For example, Australia's first cloned sheep appeared healthy and
energetic on the day she died, and the results from her autopsy failed to determine a cause
of death.
In 2002, researchers at the Whitehead Institute for Biomedical Research in Cambridge,
Massachusetts, reported that the genomes of cloned mice are compromised. In analyzing
more than 10,000 liver and placenta cells of cloned mice, they discovered that about 4%
of genes function abnormally. The abnormalities do not arise from mutations in the genes
but from changes in the normal activation or expression of certain genes.
Problems also may result from programming errors in the genetic material from a donor
cell. When an embryo is created from the union of a sperm and an egg, the embryo
receives copies of most genes from both parents. A process called "imprinting"
chemically marks the DNA from the mother and father so that only one copy of a gene
(either the maternal or paternal gene) is turned on. Defects in the genetic imprint of DNA
from a single donor cell may lead to some of the developmental abnormalities of cloned
embryos.
Artificial Insemination
Many couples encounter difficulties getting pregnant because of fertility
problems. However, few people are completely infertile, and most couples who
need help to make a baby are described as subfertile. This means that one part
of their reproductive system may not be working correctly.
Artificial insemination (AI) is a means of helping couples to have children if they
are unable to conceive through sexual intercourse. Artificial insemination refers
to a range of techniques in which the man's sperm is put into the woman's genital
tract artificially. Sperm may be placed in the neck of the womb (cervix), known as
intracervical insemination, or inside the womb itself, known as intrauterine
insemination (IUI).
Less common techniques of artificial insemination are intrafallopian insemination
and intraperitoneal insemination. These methods place the sperm near the
mouth of the fallopian tubes and ovaries. Rarely, a technique called intravaginal
insemination is used, in which sperm are placed in the female partner's vagina.
If there is a problem with the male partner's sperm, then sperm from a donor may
be used. Donor insemination (DI) may also useful for single women and lesbian
couples.
Risks
Sperm washing prior to IUI removes most of the bacteria from the semen, but it is
impossible to completely sterilise the sperm or the cervix. Occasionally, the
inseminated sperm can cause an infection in the uterus that leads to a condition
called endometritis, although this occurs in less than 1% of cases.
Symptoms of a uterine infection include lower abdominal pain, fever, vaginal
discharge, or continued vaginal bleeding or spotting. Mild cases can be treated
with oral antibiotics but more serious infections usually involve hospitalisation for
treatment with intravenous antibiotics.
Hormone drugs to stimulate ovulation are used for donor insemination, and may
also be used to increase the chance of conception for AI using the male partner's
sperm. This sometimes stimulates the release of more than one egg at a time,
which can result in multiple pregnancy and births. Multiple births can cause
complications during pregnancy and carry a higher risk of the baby being
premature, underweight or disabled. The chance of the baby dying within 28
days of birth is also increased (neonatal death).
Hormone drugs cause unpleasant symptoms in some women. These are often
short-lived, but may include hot flushes, feelings of depression and irritability,
headaches and restlessness at night. Some women have an over-reaction to the
drugs, causing them to develop ovarian hyperstimulation syndrome (OHSS). This
may lead to ovarian cysts developing, along with pain and swelling of the
abdomen. In severe cases, the ovaries swell and a large number of eggs may be
produced at once. Hospital admission to restore the balance of fluid is usually
only necessary in 1% of cases.