Several species of mammals have been
cloned by nuclear transplantation using an
adult cell as the source of the nucleus. Is
there any contribution to the genotype of
the cloned offspring from the oocyte into
which the nucleus is tranplanted? Briefly
explain.
This question delves in to two of the most fundamental questions of biology:
Are we what we are because of what we inherit or are we are because of what happens to us
during our development, this is often referred to as the Nature versus Nurture debate. It can be
extended here if we argue that what our genome is is decided at the point of conception and is
solely the fusion of the genetic material from the two gametes i.e.ovum and sperm. If we assume
that this gentotype is the fundamental content of each cell and that subsequent to this that
mitosis would give rise to identical daughter cells it does not explain the issue of why some cells
become blood cells others liver cells and others nerve cells. There must be overriding factors
that determine which genes are controlled and either switched on or off dependent on their
determined fate. In other words there has to be an influence that is external to the very genome.
Secondly identical twin studies would suggest that given an identical genotype and exposing
individuals to slightly varied environmental conditions would give rise to different individuals
phenotypically.
In the early days of scientific argument there was the argument of Lamarkism versus Darwinism
in that Lamarkism would maintain that the existence of the long necked giraffe was an
evolutionary product of the aquisiton through an animals life time of stretching and that this
facet could be passed on to the next generation hence over countless gfenerations would l;ead
to a long necked variety. This was quite at odds with Darwinism which would maitain that there
was an evolutionary pressure place on the selective advantage within a range of giraffes that
would mean that those with long necks would survive hence “ survival of the fittest” Survivors
breed and consequently ove r countless generations the long necked giraffe would survive.
Both of these issues are relevant to contemporary biology, is there influence on the genome
from the immediate environment in the case of the developing egg is there an influence on the
transplanted nucleus from the surrounding cytoplasm.
Scientists have been cloning animals for many years. In 1952, the first animal, a tadpole, was
cloned. Before the creation of Dolly, the first mammal cloned from the cell of an adult animal,
clones were created from embryonic cells. Since Dolly, researchers have cloned a number of
large and small animals including sheep, goats, cows, mice, pigs, cats, rabbits..
All these clones were created using nuclear transfer technology.
Hundreds of cloned animals exist today, but the number of different species is limited. Attempts
at cloning certain species such as monkeys, chickens, horses, and dogs, have been
unsuccessful. Some species may be more resistant to somatic cell nuclear transfer than others.
The process of stripping the nucleus from an egg cell and replacing it with the nucleus of a
donor cell is a traumatic one, and improvements in cloning technologies may be needed before
many species can be cloned successfully.
Reproductive cloning is a technology used to generate an animal that has the same nuclear DNA
as another currently or previously existing animal. Dolly was created by reproductive cloning
technology. In a process called "somatic cell nuclear transfer" (SCNT), scientists transfer
genetic material from the nucleus of a donor adult cell to an egg whose nucleus, and thus its
genetic material, has been removed. The reconstructed egg containing the DNA from a donor
cell must be treated with chemicals or electric current in order to stimulate cell division. Once
the cloned embryo reaches a suitable stage, it is transferred to the uterus of a female host where
it continues to develop until birth. See diagram that I have included below.
Dolly or any other animal created using nuclear transfer technology is not truly an identical
clone of the donor animal. Only the clone's chromosomal or nuclear DNA is the same as the
donor. Some of the clone's genetic materials come from the mitochondria in the cytoplasm of
the enucleated egg. Mitochondria, which are organelles that serve as power sources to the cell,
contain their own short segments of DNA. Acquired mutations in mitochondrial DNA are
believed to play an important role in the aging process.
Dolly's success is truly remarkable because it proved that the genetic material from a
specialized adult cell, such as an udder cell programmed to express only those genes needed by
udder cells, could be reprogrammed to generate an entire new organism. Before this
demonstration, scientists believed that once a cell became specialized as a liver, heart, udder,
bone, or any other type of cell, the change was permanent and other unneeded genes in the cell
would become inactive. Some scientists believe that errors or incompleteness in the
reprogramming process cause the high rates of death, deformity, and disability observed among
animal clones.
Other issues have arisen from this question Dolly has not told us much. The cloning of an adult
mammal from the transplanted nucleus of an adult mammalian cell is direct evidence for what
developmental biologists have long held to be true--that the nuclei of most cells in an individual
are genetically identical. The fact that the Scottish investigators do not know the developmental
state of the cell from which the nucleus came makes it even less impressive scientifically than
the amphibian experiments done 20 years ago. The experiments of Gurdon and colleagues
(1975) and Orr and colleagues (1986) used amphibian cells that were known to be fully
differentiated. Orr and her co-workers used frog erythrocytes, while Gurdon's laboratory used
cultured keratinocytes whose differentiation was demonstrated by skin-specific cytokeratins. We
do not know the differentiated state of the cell whose nucleus was used to generate Dolly. It
could be that the nucleus was from a stem cell population which, while committed to a particular
cell fate, is relatively undifferentiated.
There are some valid scientific questions that could be asked. For instance, did the nucleus
become "rejuvenated" by the egg cytoplasm. That is to say, will the lifespan of the cloned sheep
approximate that of a normal sheep or will it be shortened by the amount of time the nucleus has
already spent as an adult. It would be interesting to know the state of its telomeres. Society has
to answer its own questions, namely: (1) Is such scientific knowledge worth the risk of inventing
a technique that could clone humans? and (2) When, if ever, is the cloning of human nuclei
allowable?
The mechanism by which Wilmut and colleagues cloned Dolly is not very efficient. Out of the 277
mammary gland nuclei fused to enucleated unfertilized eggs, only one lave lamb was born.
However, the claim that our inability to clone other mammals is a technical-- rather than a
physiological-- problem suggests that more efficient cloning techniques can be developed.
There may be physiological barriers against cloning in mice and humans. Sheep, for instance,
activate their nuclei relatively late--at the 16 cell stage. This might give the egg cytoplasm ample
time to "reprogram" the chromatin. Mice, on the other hand, activate their nuclei at the late onecell stage. Humans activate some genes (such as SRY) during the one-cell stage, but the global
activation of the human genome does not occur until the 4-8 cell stage, shortly before
compaction (ocurring around the 10-cell stage in H. sapiens [Nikas et al., 1996]).
Dolly was the same as any other sheep of her chronological age, except that she had the DNA of
a six year old ewe. In 2002, however, Dolly was found to be suffering from arthritis in one of her
hind leg joints and this premature ageing was questioned. She then developed lung problems
and in July 2003 Dolly was euthanased.
Although in most ways she was the same as other sheep of her chronological age Dolly only
survived half her expected life span. Scientists reported that her premature death was triggered
by a virus caught from a sheep who had died two years earlier and it was not specifically related
to the process of cloning, but it raised the question of the wisdom of cloning. There has been no
further attempts to clone another Dolly.
Dolly
.

http://zygote.swarthmore.edu/gene4.html
http://science.howstuffworks.com/clonin
g3.htm
http://www.ornl.gov/sci/techresources/
Human_Genome/elsi/cloning.shtml
Name a technique that can be used to
simulataneously detect the transcripts of
thousands of genes in a single tissue
sample.
Genetic fingerprinting allows the detection of genes
Below is a genetic fingerprint, this technique has been widely used since it was
developed in the field of forensic science, cloning and gene therapy
I have listed below three excellent web sites that will explain genetic
fingerprinting and how it is used.
http://www.thenakedscientists.com/html/columnists/dalyacolumn8.html
http://genome.wellcome.ac.uk/doc_wtd020877.html
http://www.bbc.co.uk/cambridgeshire/content/articles/2005/11/29/naked_scientis
t_dna_feature.shtml