Cloning_what_is_it Essays - Cloning, Genetics,

Cloning_what_is_it? Cloning What is Cloning? Cloning is the production of one or more individual plants or animals that are genetically identical to another plant or animal. Nature itself is the greatest cloning agent. In about one of every 75 human conceptions, the fertilized ovum splits for some unknown reason and produces monozygotic (identical) twins. Each has a genetic makeup identical to the other. Two very different procedures have been referred to as cloning: ? Embryo cloning has been successfully carried out for years on many species of animals. Some limited experimentation has been done on human embryos. ? Adult DNA cloning has been used to clone a sheep, but was not tried on humans until December 1998. How is Embryo Cloning is Done? Human embryo cloning starts with a standard in vitro fertilisation procedure. Sperm and an egg cell are mixed together on a glass dish. After conception, the zygote (fertilised egg) is allowed to develop into a blastula (a hollow mass of cells). The zygote divides first into two cells, then four, then eight... A chemical is added to the dish to remove the zona pellucida covering. This material provides nutrients to the cells to promote cell division. With the covering removed, the blastula is divided into individual cells, which are deposited on individual dishes. They are then coated with an artificial zona pellucida and allowed to divide and develop. The experiment by Sillman showed that the best results could be obtained by interrupting the zygote at the two-cell stage. Many of these pairs of zygotes were able to develop to the 32-cell stage, but no further. They might well have had the potential to develop further and even mature into a viable foetus, except that the original ovu m was defective and would have died anyway. For ethical reasons, the researchers selected embryos which had no possibility of ever maturing into foetuses, and thus into newborn babies. How is Adult DNA Cloning Done? With the exception of the sperm and egg, every cell in the body contains all of the genetic material in its DNA to theoretically create an exact clone of the original body. But cells have been biochemically programmed to perform limited functions. The other functions are turned off. Most scientists had believed that such differentiated cells could not be reprogrammed to be capable of behaving as a fertilized egg. In the case of the sheep Dolly?, a cell was taken from mammary tissue of a mature 6 year old sheep while its DNA was in a dormant state. It was fused with a sheep ovum which had had its nucleus removed. The fertilised cell was then stimulated with an electric pulse. Out of 277 attempts at cell fusion, only 29 began to divide. These were all implanted in ewes. 13 became pregnant but only one lamb, Dolly, was born. History of Cloning Cloning has had a fairly long history: ? The first successful cloning experiment involved a leopard frog. It took place in, 1952 with group of scientist from the Institute for Cancer Research in Philadelphia. To clone the frog they used an embryonic frog cell nucleus ? In 1962, John Gurdon of Cambridge University cloned a toad that survive threw adulthood and was able to reproduce. He was also the first to take a nucleus from a fully contrast tadpole intestinal cell and cloned toads(Robertson) ? In 1981, Steen Willadsen was the first to clone an artificial chimera. He did this by mixing a sheep and a goat getting the result of a geep. It had the body shape and the head of a goat, and a dappled coat which had large patches of sheep's wool ? In 1984, Willadsen cloned the first verifiable mammal, using embryonic nuclei transplant into an unfertilised sheep egg ? In 1986, when Willadsen worked for Texas bioengineering company, he produced the first cloned calves from cattle by using the embryonic nuclei. The cloned cattle that were produced were super-elite, high production dairy cows and bulls who had a high breeding rate ? In 1987, James Robl of the University of Massachusetts was the first to clone rabbits also using embryonic nuclei Going by these past events, who can say when we will be able to clone human organs or complete biocopies of human beings