Genetic variation and its control is one of the topics studied in GCSE Science. This is the third of four quizzes on the topic and it looks at sexual and asexual reproduction and cloning.
There are two forms of reproduction: sexual and asexual. During asexual reproduction there is no fusion of gametes (sex cells) and only one individual is needed as the parent. Therefore, unlike sexual reproduction, in asexual reproduction there is no mixing of genetic information and so no genetic variation in the offspring. These genetically identical individuals are known as clones.
Humans have been cloning plants for thousands of years - taking cuttings produces new plants that are genetically identical to the original parent plant. Single celled organisms like bacteria and amoeba create clones of themselves as they reproduce by binary fission or budding.
Creating clones of animals is not an easy task. The first animal clone, a frog, was created in 1958. Fish were cloned in the 1960s and 1970s but it wasn't until the 1990s that mammals were cloned. The most famous is perhaps Dolly the sheep. The reason for that is that she was cloned from an adult cell, rather than the cells of an embryo.
There are two ways of cloning animals. Embryo transplants involve splitting apart cells from a developing animal embryo before they become specialised. The identical embryos are then implanted into host mothers to develop. The cells are fertilised naturally and no internal changes are made to the cells.
For adult cell cloning the nucleus is removed from an unfertilised egg cell. The nucleus from an adult body cell, e.g. a skin cell, is then inserted into the egg cell. An electric shock is given which causes the egg cell to begin to divide to form embryo cells. These embryo cells contain the same genetic information as the adult skin cell. When the embryo has developed sufficiently, it is inserted into the womb of an adult female host.
Science fiction writers have for many years explored the possibility of the cloning of people which could theoretically be done by either method. But this raises lots of moral and ethical issues - you should have discussed some of them in class.
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