Cloning

Cloning, the process of “Manipulating a cell from an animal so that it
grows into an exact duplicate of that animal is the forbidden fruit of biology.”
(Begley 54). The word “clone”, derived from the Greek word “Klon”,
meaning twig or slip, refers to asexual reproduction. Also known as vegetative
reproduction. Cloning became known to the public about 30 years ago. This idea
of cloning about his time resulted in an experiment of the successful asexual
reproduction. This experiment took place in England, where a whole bunch of
tadpoles was cloned by the technique of nuclear transplantation. Nuclear
transplantation refers to the process of moving a nucleus from one cell to
another. (Mckinnel 28) The person responsible for this introduction of cloning
was Joshua Lederberg, a noble laureate geneticist. (Kass, Winters 9)

Scientists have known for a long time what it took to clone, and many had
found themselves believing that it was biologically impossible. One problem was
the way the embryo develops. Every cell in the body comes from the same
fertilized egg therefore, every cell in the body contains the same genes. But
animal and human cells are specialized and different, so that a heart cell acts
as a heart cell and a liver cell acts as a liver cell. This specialization
starts when the fetus is formed, and once a cell reaches its final state, it
never changes. A brain cell will always be a brain cell as long as a person is
living, it would never change into a liver cell although it contains the same
genes. (Kolata 24)

Frogs were the first multicellular animals to be cloned in the 1950’s. A
thorough cloning experiment produces a frog asexually. No gamete nucleus, sperm
or egg, participates in the development of a frog that is truly a clone. (Mckinnel
3) The cloning procedure in frogs, toads, and salamanders is very difficult. In
order to start this cloning process, the ability to obtain eggs and sperm from
frogs had to be introduced. Also the process of vitro fertilization, removal of
maternal chromosomes from eggs, and the splitting of embryos into individual
cells. (140) To obtain frog eggs, the eggs have to grow to their maximum size
and the frogs are ready for hibernation under the ice of lakes and streams.
Ovulation can be induced from September to or past the time of natural
ovulation. Eggs leave the ovary, move to the reproductive tubes, and become
available to the embryologist when the female frog is injected with pituitary
glands or a combination of pituitary glands and the hormone progesterone. The
eggs can be removed from the female after this treatment by gently squeezing the
abdomen. (41)

Frog sperm can be obtained by cutting the testes of the frog into small
pieces in a diluted salt solution. The testes are dissected from the male, which
usually requires sacrifice of the frog donor. Then, a commercially available
hormone present in pregnant humans, is injected into a mature male frog. Within
one hour, millions of sperm are released from the testes of the frog and found
in the frog’s urine. This sperm is then capable of fertilizing frog eggs.
(41-42)

Eggs and sperm can be combined in a glass dish at a precise time. By caring
for the fertilized eggs at a particular temperature and time, donor embryos of
predetermined stages can be obtained. Using glass dishes is a simple and
efficient way of producing the frogs since frog eggs are very large and contain
an immense amount of stored food. (42)

The next step to the cloning of frogs is to prepare the frog eggs to receive
a transplanted nucleus. Freshly ovulated eggs have the same amount of DNA as an
ordinary body cell. That amount of DNA is twice the amount found in a sperm; so
it is called diploid. A sperm contains the haploid amount of DNA. The fact that
the ovulated eggs are diploid, helps with the experiment greatly. If diploid
eggs could combine with diploid sperm, than the amount of DNA in the offspring
would become enormous in only a few generations, but this does not happen. What
happens is that the frog egg becomes haploid as the sperm already is, after it
is released from the ovary and at that time it is activated by the penetration
of the sperm. This results in an egg devoid of any genetic material in the form
of chromosomes. This egg only has to be removed from the jelly envelope that
surrounds it by cutting it with scissors, in order for it to be ready to be
transplanted in to a nucleus. (42-43.)

After