Biology
Understanding cloning
We are learning how to: • Define cloning and describe some natural cloning processes. • Explain how organisms may be artificially cloned. • Explore ethical issues around artificial cloning. • Compare and contrast asexual and sexual reproduction.
Many organisms can reproduce without a female sex cell fusing with a male sex cell to produce offspring. How do they do this? Why do they do this? Why do we need sexual reproduction? Natural clones
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A clone is an identical copy that has been created of an organism. Some organisms can produce new individuals without using sex cells – this is called asexual reproduction. This means that every cell in every organism has exactly the same set of genes. The new individual is called a natural clone. An example of cloning in plants is when a spider plant has small plants dangling from the end of ‘runners’ coming from the parent plant. All the small plants look the same. Strawberry plants also spread by using runners. The new plants rely on the parent plant until their own root system is fully formed. Plant clones are also formed by bulbs, corms, tubers and rhizomes.
FIGURE 3.1.12a: The dandelion can re-grow from small sections of root – each new plant is a replica of the original plant.
Asexual reproduction in animals happens less often. It occurs in sea anemone, hydra and starfish, for example. Identical twins are are natural clones because they are formed after one fertilised egg cell splits into two cells. As a result they are genetically identical. 1. What is a clone? 2. Why are clones identical?
Artificial clones
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Clones can also be made artificially. The simplest way to clone a plant artificially involves taking a cutting. A branch from the parent plant is cut off, its lower leaves removed and the stem planted in damp compost to allow roots to develop. Plant clones can also be produced by tissue culture.
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Did you know...? The first artificial cloning of an animal was done in the 1890s by Hans Driesch who cloned a sea urchin from a single sea urchin embryo cell.
KS3 Science Book 3: Variation for Survival
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24/04/2014 10:50