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In this article we will discuss about plant and animal cloning.
In plants, agronomically important traits are governed by the genetic information stored in the nuclear and organellar (i.e., chloroplasts and mitochondria) genome and gene transfer can be done in all these genomes.
However, gene transfer in organelles specially in mitochondria is relatively difficult as compared to nuclear genetic transformation. The uptake of genes by cells in microbes and plants is termed as transformation.
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Steps in plant genetic engineering:
The important steps involved in plant genetic engineering are as follows:
1. The first step is the identification and isolation of agronomically important gene.
2. The second step is cloning the isolated gene in a plant transformation vector.
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3. The third important step is introduction of the gene into plant protoplasts, cells or tissues using gene transfer methods.
4. Now comes culture and regeneration of complete plants from genetically transformed cells on suitable selection medium.
5. The last important step is demonstration of the integration and expression of foreign gene in the transgenic plants by using molecular techniques.
Applications of Plant Genetic Engineering:
Till now, the plant genetic engineering has been successful in producing disease and pest resistant as well as herbicide tolerant transgenic plants. For example, in tomato the slow ripening process of the fruits is developed; in soybean, corn and cotton herbicide tolerance is developed; in potato, tomato, tobacco and rice viral resistance is developed.
Animal Cloning and Genetic Engineering:
Animal Cloning:
Animal cloning is more difficult than plant cloning because animal cells lose their totipotency on reaching the gastrula stage of animal development. However, animal tissue cultures from tumours and embryonic tissue cells have been successful. Standard techniques are available for isolating animal cells and tissues from different systems.
Some more important examples of animal cloning are tissue culture, somatic cell fusion, cell cloning and creating transgenics.
Gene Transfer in Animals:
Gene transfer in animals is mostly through direct methods such as electroporation or microinjection or using particle gun. In creating ‘Dolly’ the cloned sheep, fertilised egg of its mother was removed by micro-needle and nucleus from an udder cell of a donor sheep was microinjected in the egg after removing egg nucleus. The egg developed into ‘Dolly’ with genes identical to its mother.
Applications of Animal Cloning and Genetic Engineering:
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Examples of animal products (medicines) produced through genetic engineering are:
(i) Chick embryo fluid which produces vaccines for influenza, measles and mumps,
(ii) Duck embryo fluid which produces vaccines for rabies and rubella.
How Sheep ‘Dolly’ Cloned?
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Ian Wilmut and his associates at the Roslin Research Institute, Scotland, took cells from ewe (mother sheep’s udder). An udder cell is different from a skin cell or a muscle cell or a nerve cell.
They managed to store these udder cells in nutrient deprived culture. This checked the starved cells from dividing, and switched off their active genes.
Now, one udder cell complete with its nucleus was selected, as this nucleus carries the mother’s genetic information.
Meanwhile, unfertilized egg cell was taken from a different ewe (host mother sheep). Its nucleus was sucked out leaving an empty cell containing all the necessary components to produce an embryo. This cell was now ready to receive udder cell nucleus.
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They now fused udder cell nucleus with the empty egg cell by electrical stimulation. Then this egg cell had the mother’s nucleus.
When a normal or altered egg is implanted in a different female is termed ‘surrogate mother’. This means, substitute mother.
Then the altered egg was cultured for six days. Out of many resulting embryos, one was implanted in the uterus of the surrogate mother, where it grew into a lamb.
Thus, Dolly was born genetically identical to mother sheep as her first cell nucleus came from mother’s cell.
How Calves are Cloned in Japan?
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Scientists from Japan have cloned cattle in a different way.
They have got success in growing as many as eight identical calves from one fertilized cell of their mother.
The process is as follows:
When the mother cow has mated with the bull, she has a fertilized egg in her womb. Now this zygote divides in two and then in four and then in eight. This embryo is carefully removed from the womb, and the embryonic cells are separated using as enzyme.
Each isolated cell is kept in a nutrient medium and later implanted in the womb of a different ‘host mother’ cow.
The host mother’s womb must accept the cell and make it grow. Each cell may grow into a normal baby calf, if all goes well.
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First Human Clone:
The birth of the first human clone (December 26, 2002), a baby girl called Eve by scientists, was announced by Brigitte Boisselier, head of a company named Clonaid. According to Boisselier, the child is an exact genetic duplicate of her mother.
To clone, scientists slip the nucleus of an adult cell, like a skin cell, into an unfertilized egg from which its own genetic material has been removed.
Then, if stimulated to act like a fertilized egg, the newly altered genetic material can then direct the egg to divide and grow into an embryo, then a foetus, then a newborn, if all goes well. Yet, as scientists have discovered, only rarely does all go well.
In animal work so far only about 1 to 5 per cent of cloning attempts succeed, said Randall Prather, a cloning expert. That is, for every 100 eggs, one to five clones are born.
