A clone is a genetically identical copy of a living organism. Human
clones are nothing new; they occur naturally in the recognizable form
of identical twins. Not until the successful cloning of a sheep called
Dolly, however, has the possibility of intentionally producing an
identical copy
of a human been considered seriously.
Production of a human clone would most likely utilize the same basic
methodology that resulted in Dolly. A human egg would be retrieved
from an individual, and its genetic material (DNA) would be removed
and replaced with DNA derived from any adult human cell type. This
would bypass the need for fertilization of the egg by the sperm in
order
to obtain a full complement of DNA. In a laboratory dish, the egg
would then undergo several cell divisions. Placed into a uterus, the
resulting embryo would grow and, with luck, develop until birth.
Although this cloning technique is conceptually and procedurally
simple, its success rate has been extremely low. The birth of one
Dolly, for instance, required the preparation of 277 re-nucleated
eggs, followed by the implantation of 29 resulting best embryos. The
low success rate can be attributed to the difference between the young
DNA of a normally fertilized egg and the genetic material of the
re-nucleated egg, which is mature and of defined destiny – it has
already committed itself to a particular physiological role. In order
for proper fetal development
to occur, mature DNA must be coaxed into reverting to its youthful
state, a complex process that will be difficult to achieve for the
human species.
Beyond the practical difficulties of intentional human cloning,
scientists, politicians, and others have raised serious ethical
concerns about this practice. For example, there is a chance that the
cloning procedure would adversely affect the developing embryo. There
also might be deleterious effects on the long-term health of the
clone. Proponents of human cloning counter that human sexual
reproduction is not a risk-free affair either. Even if human cloning
could be made safe, the motivations behind producing human clones do
not fall clearly on one side of the ethical divide. While proponents
stress potentially
appealing motivations – a man and a woman who are both carriers of a
genetic disease can use cloning to assure that their child will not be
afflicted with the disorder – critics argue that the practice could
and likely would be used for unethical ends, such as to select for
certain traits, such as hair/eye color or sexual orientation, for
example.
1. The primary purpose of the passage is to
a) dismiss a new scientific method as unethical
b) defend a medical procedure against unwarranted attack
c) explain a process and its ramifications
d) describe a hypothesis and its negative consequences
e) analyze the possible outcomes of a new medical approach
2. The author of the passage mentions Dolly most probably in order to
a) suggest that human cloning is feasible
b) show that the ethical concerns against cloning are misguided
c) argue that nonhuman cloning is less efficient than human cloning
d) establish a basis for an argument against human cloning
e) refute a counterargument in favor of human cloning.
3. According to the passage, which of the following is a potential
obstacle to human cloning?
a) Lack of adequately prepared human eggs
b) Predetermination of DNA function within the adult body
c) Shortage of funding for additional research
d) Inability to pinpoint specific biological relationships within an egg
e) Unpredictability of chemical reactions within the uterus
4. The passage suggests which of the following?
a) Human cloning is reachable within ten years.
b) The cloning of nonhuman animals has always been successful.
c) The eggs of nonhuman animals are easier to obtain than human
eggs.
d) DNA taken from an adult human cell contains DNA from both parents.
e) Human DNA is less predictable than nonhuman DNA.
5. Which of the following is NOT given in the passage as a reason not
to pursue human cloning?
a) The unknown effects of cloning on adult human clones.
b) The potential harm to cloned embryos.
c) The chance that cloning will be used to select for only certain
socially advantageous characteristics.
d) The technical difficulty of obtaining suitable DNA.
e) The exorbitant costs associated with the medical procedures used in cloning.
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