n the year and a half since Scottish embryologist Ian
Wilmut presented Dolly, the cloned sheep, to an astonished
world, ethicists and policymakers have been struggling with
the unsettling implications of his research. Could scientists
use Wilmut's method to clone not just sheep but also
billionaires, basketball players and bodies grown for spare
parts? Should medical entrepreneurs be allowed to pursue
cloning wherever it leads? Or should the government step in
now and outlaw it before it starts?
For reproductive biologists, these issues pale in the face of
two more immediate and practical questions: Is Dolly really
a clone--and if so, can anybody make one? It's taken a while,
but the answers are finally in. The verdict, according to a
trio of reports in the current issue of Nature: yes and yes.
Not only have Dolly's pedigree and her immaculate
conception been established beyond all reasonable doubt,
but she has been joined by litter upon litter of perfectly
cloned mice. Cloning has, with a speed no one anticipated,
been transformed from an astonishing technical tour de
force into what seems almost a mundane laboratory
procedure.
CLONING
For decades, the cloning of adults — animals or humans —
has been largely the stuff of science fiction. Since the
successful cloning of a six-year-old sheep, many of the
assumptions and questions being raised have roots in the
fictional: Could parents one day clone their fatally ill children?
Could Hitler or the Incan Ice Mummy be brought back to life?
Would humans be cloned solely to cannibalize their organs?
TIME examines the most controversial topic in the field of
science.
TYPES OF CLONING
Human cloning can either be reproductive or
theraputic (2). In reproductive cloning, an embryo
that has been cloned is implanted into a woman's
womb. Thus, a living human being will be produced
(providing there are no complications) as a cloned
child (2). This is a form of asexual reproduction, as
shown below.
MOLECULAR CLONING
Molecular cloning—not to be confused with cell
cloning or whole animal cloning—is an important
tool in our endeavour to understand the structure,
function and regulation of individual genes and their
products. An important resource is the creation of a
DNA library, which is a complete collection of DNA
fragments, each located singly within a cloning
vector that is capable of replication when
transferred to an appropriate host cell. Two distinct
types of library can be formed, depending on
whether the cloned DNA was derived by
fragmentation of the genome (genomic library) or
was copied from cellular messenger RNA (cDNA
library). The following basic steps are involved in
the molecular cloning of genes
Embryo Cloning
Cloning embryos is similar to what happens naturally when
identical twins are created in the womb. We all start as a
one-celled organism. Normally, the cell divides and
differentiates to make one human. With identical twins, as
the cell divides it separates into two separate, individual
cells. The two separate, individual cells continue to divide
and differentiate independently, and develop into two
unique humans with identical genetic makeups, identical
genomes .
In contrast, embryo cloning is mechanically forcing a cell to
divide into two separate, individual cells. These grow and
develop separately, thereby creating identical twins.
Once an egg has been fertilized by sperm it soon starts
dividing. If it divides into an eight cell embryo and those
eight cells are separated, those cells can be implanted into
the uteri of eight separate mothers. Then eight clones will be
born of different mothers.
Uses of Cloning
All of the uses of cloning are still unknown, as
until (or if) the process is complete, there are endless
possibilities in the new technology. Through the links
mentioned within this site, many uses for cloning were
addressed, some more practical than others, ranging
from cloning of specific organs to end the need for
donors to creating the genetic replica of a recently
deceased love one. Any advancement in genetic
engineering will aid in continuing to develop
methods of gene therapy.
• The mass production of animals engineered to carry
human genes for the production of certain proteins that
could be used as drugs; the proteins would be extracted
from the animals' milk and used to treat human diseases.
• The mass production of animals with genetically modified organs
that could be safely transplanted into humans.
• The mass production of livestock that have been genetically
modified to possess certain desirable traits.
• The perpetuation of endangered species.
• The production of offspring by infertile couples.
• The production of offspring free of a potentially disease-causing
genetic flaw carried by one member of a couple; the individual
without the defect could be cloned.