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A clone of cells is derived from a single cell through mitosis or binary fission, etc. and all
cells of a clone are genetically identical (except for the changes that may arise during and after
cloning). The process of obtaining clone of cells from a single cell is known as cloning. Cloning has

been successfully done in microbes, plants as well as in animals.

1.    Microbial Cloning: Microbial cloning has been most successfully and most extensively utilized for the welfare of human beings, e.g. culturing of clones of genetically unmodified Escherichia coli cells are used in recombinant DNA technology. Moreover, the recombinant DNA is also obtained in multiple copies after introducing it into a suitable bacterial cell and it is also known as gene cloning, e.g. cloning of E. coli cells containinghuman insulin gene.

2.    Plant Cloning: In plants, for cloning purpose cells from leaf or stem or root or flower parts are separated from the tissues and a single cell is cultured in artificial nutrient medium to obtain a clone of cells. Clonal plants can be obtained when each cell of this clone is allowed to regenerate into a complete plantlet by putting it in a nutrient medium containing correct proportion of hormones, like auxins (induces cell growth) and cytokinins (induces cell division). Plant cloning is utilized extensively in agriculture and forestry to get unlimited number of clonal plants in a short duration of time, particularly for rare and slow growing plants. (Details in the chapter Biotechnology in Agriculture and Forestry’)

3.     Animal Cloning: When a complete animal is obtained from a somatic cell of an animal the technique is called animal cloning. Only a limited success has been achieved in this field. Sometimes, animal cloning is highly desirable to get indefinite number of desirable similar type of animals by the cloning (which does not involve the genetic changes due to meiosis occurring at a particular stage in higher organisms at the time of gametes formation during sexual reproduction). Human cloning is illegal. In 1997, Ian Wilmut and and colleagues (British scientists) successfully developed a clonal sheep after transferring the nucleus from an udder cell of a female sheep into the protoplasm of a enucleated unfertilized egg. This egg was then transplanted in the uterus of another female sheep (surrogate 


Fig. 12.16 Development of a sheep clone, Dolly.

After Dolly, the Japanese scientists developed eight clonal calves in 1999 by embryo splitting technique, where, at the 8-celled stage of the sexually obtained embryo, the cells were separated and each cell was introduced into the uterus of a separate cow to get eight clonal calves identical to each other (Fig. 12.17).


American scientists reported the cloning of rhesus monkey, that is closest to human beings, in 2000 by embryo splitting technique. In this technique, the normal zygote produced after the sexual reproduction was allowed to divide mitotically and at 4-celled stage, the four cells of the embryo were separated. Each cell was then introduced into the uterus of a separate surrogate mother for the development of cell into a baby monkey.