| When complete animals are obtained from
somatic cells of an animal, it is termed as
animal cloning.
Cloning is routine in plants, but in case of animals only a
limited success had been achieved so far. earlier, nuclei from
tadpole were transplanted into the cytoplasm of an enucleated
fertilized frog egg, and normal frogs were obtained.
But early in 1997, British scientists announced successful
cloning of sheep by transferring the nucleus from the udder
cell of an adult sheep into the cytoplasm of an eunucleated
fertilized egg. The egg was then transplanted into the uterus
of a surrogate mother where it developed like a normal zygote
into a normal lamb, which grew into a normal adult sheep,
called 'Dolly' |
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| Cells from mammary gland of an adult sheep( 6yr old ewe) were
first cultured in vitro. The cultured cells were arrested ,
induced to enter the G0 phase (quiescent phase) by
reducing the concentration of serum in the medium from 10% to 0.5%
for 5 days. The G0 cells were then fused in vitro with the
ennucleated ova of appropriate stage. oocyte were recovered
between 28 to 33 hr after injection of gonadotropin
releasing hormone and enucleated as soon as possiblecell fusion
was induced by electrical pulse, which also activated the
oocytes.The fusion product were cultured invitro in ligated
oviducts of sheep upto morula or blastula stage befor their
transfer into the uteri of the surrogate. the rate of success in
obtaining normal embryo development was rather low: a total of 277
oocytes were fused with cultured mammary gland cells: of these 29
reached morula/blastula stage, and were transferred into surrogate
mothers leading to 13 pregnancies, but only one live birth. |
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Cloning in many situations, highly desirable sincethis allows
(1) indefinite multiplication of an elite desirable genotype
without the risk of segrgation and recombination during meiosis,
which must precede sexual reproduction. Obviously (2) the
technique holds a great promise in genetic research, and impact of
epigenetic changes, such as, imprinting and telomere shortening,
etc. In addition, (3) This technique should make it feasible to
target transgenes in livestock by nuclear transfer from transgenic
cell populations developedinvitro into enucleated oocytes to
recover nonchimaeric transgenic animals. Obviously this approach
would oviate the generations of breeding necessary for the recovey
of transgenic animals from the chimaeric ones that are generated
by embryonic stem cell transfer. |
It has been suggested that inducing the differentiated nucleus
of donor cells to enter G0 Phase causes such changes in chromatin
structure that facilitate reprogramming of gene expression.
Therefore, If nuclei from G0 cells were transferred into
enucleated oocytes, the resulting diploid cell may be expected to
develop like a normal animal. The technique needs to be refined &
expanded to other animals. however, in most countries, especially
in all developed countries, human cloning is illegal. Following
the above report American scientist announced successful cloning
of rhesus monkey using the embryo splitting technique: this is the
closest species to humas where embryo splitting has been
successful. however some groups have claimed success in human
cloning as well |
