The reproduction of living organisms through sexual cells is widely
spread in animal and plant kingdoms. Lately, widely discussed is the
problem about so-called cloning, i.e. obtaining viable progeny from single
vegetative (somatic) cells of definite cell lines obtained through genetic
methods and manipulations. It is outlined that cloning has not only scientific
and practical, but also social importance if it is applied to the man.
For the present, in animal organisms cloning is realized through
transplanting nuclei of somatic embryonic cells in enucleated unfertilized
eggs. The development of this problem begins after the 1950s, when the
role of nucleus for determining characteristic features of individual cell or
organism was proven. The difficulties in this direction met by the
investigators are connected mainly with the specificity of organism in
dependence of its position in evolutionary hierarchy and the development
stage of embryonic cells used as donor of nuclei. The earlier stage of
embryonic development is, the better the results are.
After the encouraging success of experiments with the unicellular
green alga Acetabularia and different amphibia (mainly frog tadpoles) the
investigators direct their attention to higher animal organisms — mice,
sheep, cows, etc. Willadsen (1986) obtained a lamb through cloning, by
using as donor cells nuclei of embryo in early morula stage (8 cells). Wilmut
and co-authors (1997) extended the age limits. They proved the possibility
to obtain a viable lamb not only from embryonic cells in early stage, but
also from adult animal cells (Fig. 4–4). The cloned lambs possesses the
same genotype as the donor-cells and differ from that of recipient.
According to the authors “the fact that a lamb was derived from an adult cell
confirms that differentiation of that cell did not involve the irreversible
modification of genetic material required for development”.
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Figure 4–4. Lamb number 6LL3 derived from the mammary gland of a Finn Dorset ewe with the Scottish Blackface ewe which was the recipient. The lamb possesses the donor-cell genotype differing from that of recipient (After Wilmut et al., 1997).