Cloning describes the processes used to create an exact genetic replica
of another cell, tissue or organism. The copied material, which has the
same genetic makeup as the original, is referred to as a clone. The
most famous clone was a Scottish sheep named Dolly.
Cloning in biology is the process of producing populations of
genetically-identical individuals that occurs in nature when organisms
such as bacteria, insects or plants reproduce asexually. Cloning in
biotechnology refers to processes used to create copies of DNA
fragments, cells, or organisms. More generally, the term refers to the
production of multiple copies of a product such as digital media or
software.
There are three different types of cloning:
* Gene cloning, which creates copies of genes or segments of DNA
* Reproductive cloning, which creates copies of whole animals
* Therapeutic cloning, which creates embryonic stem cells. Researchers
hope to use these cells to grow healthy tissue to replace injured or
diseased tissues in the human body.
Cloning and Stem Cells are two rapidly growing areas of biomedical
research with profound implications for human health and well-being.
Published articles cover all aspects of cloning along with the biology,
culture, and differentiation of stem cells from all stages of
development from germ cell to embryo and adult.
Cloning is the creation of an organism that is an exact genetic copy of
another. This means that every single bit of DNA is the same between
the two!
You might not believe it, but there are human clones among us right
now. They weren't made in a lab, though: they're identical twins,
created naturally. You may have first heard of cloning when Dolly the
Sheep showed up on the scene in 1997. Cloning technologies have been
around for much longer than Dolly, though.
How does one go about making an exact genetic copy of an organism?
There are a couple of ways to do this: artificial embryo twinning and
somatic cell nuclear transfer.
The term clone is used in horticulture to mean all descendants of a
single plant, produced by vegetative reproduction or apomixis. Many
horticultural plant cultivars are clones, having been derived from a
single individual, multiplied by some process other than sexual
reproduction. As an example, some European cultivars of grapes
represent clones that have been propagated for over two millennia.
Other examples are potato and banana. Grafting can be regarded as
cloning, since all the shoots and branches coming from the graft are
genetically a clone of a single individual, but this particular kind of
cloning has not come under ethical scrutiny and is generally treated as
an entirely different kind of operation.
Many trees, shrubs, vines, ferns and other herbaceous perennials form
clonal colonies. Parts of a large clonal colony often become detached
from the parent, termed fragmentation, to form separate individuals.
Some plants also form seeds asexually, termed apomixis, e.g. dandelion.
Cloning a cell means to derive a population of cells from a single
cell. In the case of unicellular organisms such as bacteria and yeast,
this process is remarkably simple and essentially only requires the
inoculation of the appropriate medium. However, in the case of cell
cultures from multi-cellular organisms, cell cloning is an arduous task
as these cells will not readily grow in standard media.
A useful tissue culture technique used to clone distinct lineages of
cell lines involves the use of cloning rings. According to this
technique, a single-cell suspension of cells which have been exposed to
a mutagenic agent or drug used to drive selection is plated at high
dilution to create isolated colonies; each arising from a single and
potentially clonally distinct cell. At an early growth stage when
colonies consist of only a few of cells, sterile polystyrene rings,
which have been dipped in grease are placed over an individual colony
and a small amount of trypsin is added. Cloned cells are collected from
inside the ring and transferred to a new vessel for further growth.
Somatic cell nuclear transfer can also be used to create a clonal
embryo. The most likely purpose for this is to produce embryos for use
in research, particularly stem cell research. This process is also
called "research cloning" or "therapeutic cloning." The goal is not to
create cloned human beings, but rather to harvest stem cells that can
be used to study human development and to potentially treat disease.
While a clonal human blastocyst has been created, stem cell lines are
yet to be isolated from a clonal source.
Organism cloning refers to the procedure of creating a new
multicellular organism, genetically identical to another. In essence
this form of cloning is an asexual method of reproduction, where
fertilization or inter-gamete contact does not take place. Asexual
reproduction is a naturally occurring phenomenon in many species,
including most plants.
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