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Unlock This CourseCloning means making new organisms that have exactly the same genes as the parent. Clones are genetically identical, so there is no variation between them. People use cloning to make many copies of a plant or animal that has useful features, such as a plant with a good flavour or an animal with high-quality wool.
In this lesson you will meet four different ways of cloning. Two are used on plants and two are used on animals.
Key terms:
Small groups of cells are taken from part of a plant. They are grown into new plants that are identical to the parent. This is important for preserving rare plant species, because many copies can be made from a tiny piece of one plant. It is also used commercially in nurseries to produce lots of identical plants quickly.
This is an older, but simple, method used by gardeners. A piece is cut from a parent plant and grown into a new plant. One parent plant can produce many identical new plants, and gardeners need very little equipment to do it.
Both methods use only one parent and no gametes. That is why every new plant has the same genes as the parent.
Animals can be cloned at the embryo stage. Cells are split apart from a developing animal embryo before they become specialised. Each of these cells can then grow into a new animal. The identical embryos are transplanted into host mothers, who carry them until they are born.
The young animals that are born have the same genes as each other, because they came from the same embryo. They are not copies of the host mothers who gave birth to them.
Splitting the embryo before the cells become specialised is the key point. Specialised cells can only do one job, so unspecialised cells are needed to grow into a whole new animal.
Adult cell cloning makes a new animal that is a copy of an adult. The steps are:
The egg cell's own nucleus is taken out, so the new animal gets its genes from the adult body cell and not from the egg.
Remove the egg nucleus, insert the adult nucleus, give an electric shock, let the embryo grow into a ball of cells, then place it in a womb.
You need to be able to explain the potential benefits and risks of cloning in agriculture and in medicine, and to say that some people have ethical objections.
Farmers can produce many copies of plants or animals with the best features, such as a good flavour or high-quality wool. Rare plant species can be preserved. In medicine, cloning gives copies of animals or plants with the same useful features, which means the same genes every time.
Clones are genetically identical, so they have the same weaknesses. One disease could wipe out a whole group of clones. Cloning also reduces the number of different alleles in a population.
Some people think it is wrong to clone animals, or that it is unnatural to interfere with life in this way. Some people also have ethical objections to the idea of cloning humans. Ethical objections are about what people believe is right or wrong, not about what science can do.
Students often say that the clone has the genes of the egg cell. In adult cell cloning the egg nucleus is removed, so the genes come from the adult body cell. Another mistake is saying that animals from an embryo transplant are copies of their host mother. They are copies of each other, not of the host mother.
(a) Describe how adult cell cloning is used to make a cloned sheep. [4 marks]
(b) Give one advantage and one risk of cloning farm animals. [2 marks]
(a) The nucleus is removed from an unfertilised egg cell (1). The nucleus from an adult body cell, such as a skin cell, is inserted into the egg cell (1). An electric shock makes the egg cell divide to form an embryo (1). The embryo, when it is a ball of cells, is inserted into the womb of a female sheep (1).
(b) Advantage: many animals with the best features, such as high-quality wool, can be produced (1). Risk: the clones are genetically identical, so one disease could kill them all (1).
For a description of adult cell cloning, give the steps in the right order and say which cell the nucleus comes from at each stage.