The diagram below shows the process of cloning a useful gene.
Vegetative Propagation
Plant propagation is the science of establishing plant life and increasing the number of plants that are used in daily life. The methods of propagation involved fall into two categories: sexual and asexual.
Sexual Propagation
This makes for the possibility of endless combinations of genotypes; that is, in the process of fertilisation, the genes of the parent plants recombine randomly, creating new genetic entities similar to but differing from one another and from the parents as well. This diversity contributes to the development of new plant forms and species. In nature, such diversity enables plants (and animals) to respond to changes in the environment, such as diseases, insect epidemics, and changes in the climate or habitat.
Asexual Propagation
In order to continue a species of plant with desirable traits, the plant must be propagated by asexual, or vegetative, means. In this way, an apple was perpetuated and multiplied from the single branch where the mutation first appeared, to produce thousands of other apple trees by the process called grafting.
The most technical method of vegetative propagation involves cloning. Any plant tissue with cells that can divide can be used for tissue culture. A nutrient medium containing essential salts and amino acids is prepared in an agar solution, which is placed in a flask and sterilised. Sections of tissue are cut under aseptic conditions and placed on the surface of the medium. The flasks are covered with cotton wool and placed in a controlled environment. Within a short period of time the callus propagate; it is then cut into small pieces and transferred to a medium rich in auxin, a chemical that promotes root formation, or kinetin, which promotes shoot initiation.
Once roots and tops have developed, the plantlet is removed from aseptic conditions and planted under controlled conditions in a greenhouse. Tissue culture can be accomplished readily with such species as grapes, orchids, chrysanthemums, asparagus, and carrots. With other species, especially the long-lived perennials such as oak and chestnut, it is a very difficult procedure.
Other plant propagation techniques
Cuttings- remove branches of the plant and re-grow in a nutrient medium. The exact same plant grows.
Layering- natural process- the plants lower branches reach the ground and root themselves. Another identical plant grows.
Division- splitting up a large or bushy plant, similar to taking cuttings.
Cloning Animals
In 1997 scientists successfully created ‘Dolly’ the sheep produced from the udder cells of a donor sheep.
Is Human Cloning possible?
Scientists began cloning frogs in the 1950s. When a team from the Roslin Institute in Edinburgh successfully cloned an adult mammal for the first time in 1996, the possibility of human cloning came a step closer to reality. No one has managed to clone a human being yet, but several groups have announced that they plan to do so.
What is stem cell manipulation?
Stem cells are the master cells found in early stage embryos. They evolve into all the different tissues of the body, and doctors hope to treat many diseases by directing the cells to develop into needed implants, such as nerve tissues for paralysed individuals.
At present, scientists usually obtain them from human embryos discarded during fertility treatments. However, human cloning techniques could create a continuous supply of stem cells for such research.
What are the techniques used in cloning?
Roslin technique
The cloning of ‘Dolly’.
First, a cell (the donor cell) was selected from the udder cells of a Finn Dorset sheep to provide the genetic information for the clone. For this experiment, the researchers allowed the cell to divide by mitosis and form a culture in vitro. This produced multiple copies of the same nucleus.
A cell was taken from the culture and then starved in a mixture, which had only enough nutrients to keep the cell alive. This caused the cell to begin shutting down all active genes and enter the dormant stage. The egg cell of a Blackface ewe was then enucleated and placed next to the donor cell. One to eight hours after the removal of the egg cell, an electric pulse was used to fuse the two cells together and, at the same time, activate the development of an embryo.
If the embryo survives, it is allowed to grow for about six days, incubating in a sheep's oviduct. It has been found that cells placed in oviducts early in their development are much more likely to survive than those incubated in the lab. Finally, the embryo is placed into the uterus of a surrogate mother ewe. That ewe then carries the clone until it is ready to give birth. Assuming nothing goes wrong, an exact copy of the donor animal is born. This newborn sheep has all of the same characteristics of a normal newborn sheep.
Nuclear transfer
First explored by Hans Spemann in the 1920's, nuclear transfer is the technique currently used in the cloning of adult animals. Nuclear transfer requires two cells, a donor cell and an egg cell. The egg cell works best if it is unfertilised, because it is more likely to accept the donor nucleus as its own. The egg cell must have the genetic information eliminated (removed). The donor cell is then forced into a dormant phase. This dormant phase causes the cell to shut down but not die. In this state, the nucleus is ready to be accepted by the egg cell. The donor cell’s nucleus is then placed inside the egg cell, either through cell fusion or transplantation. The egg cell is then prompted to begin forming an embryo. When this happens, the embryo is then transplanted into a surrogate mother. If all is done correctly a perfect replica of the donor animal will be born.
Honolulu Technique
In July of 1998, a team of scientists at the University of Hawaii announced that they had produced three generations of genetically identical cloned mice.
Mice had long been held to be one of the most difficult mammals to clone due to the fact that almost immediately after a mouse egg is fertilized, it begins dividing.
Unfertilised mouse egg cells were used as the recipients of the donor nuclei. After being enucleated, the egg cells had donor nuclei inserted into them. The donor nuclei were taken from cells within minutes of the each cell’s extraction from a mouse. After one hour, the cells had accepted the new nucleus. After an additional five hours, the egg cell was then placed in a chemical culture to jumpstart the cell’s growth, just as fertilisation does in nature.
After being jumpstarted, the cells develop into embryos. These embryos can then be transplanted into surrogate mothers and carried to term.
In conclusion, the study of human cloning is still relatively new, it is illegal in many countries and there is an ongoing debate about the morals of cloning. There are however many ways in which cloning can be of practical use for, production of offspring by infertile couples, the continuance of endangered species and the mass production of animals with genetically modified organs which could be used in humans. Finally, no one can possibly predict the future of cloning. I believe that cloning should be researched further, before it can successfully be of practical use to humans.
