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Science

Cloning and stem cells

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Cloning occurs naturally in some plants and in human identical twins, and it is now possible to clone animals artificially. The subject of cloning raises a number of ethical issues that need to be considered.

Clones

Clones are genetically identical individuals. Bacteria, plants and some animals can reproduce asexually to form clones that are genetically identical to their parent. Identical human twins are also clones: any differences between them are due to environmental factors.

Asexual reproduction only requires one parent, unlike sexual reproduction, which needs two. Since there is only one parent, there is no fusion of gametes, and no mixing of genetic information. As a result, the offspring are genetically identical to the parent, and to each other - so they are clones.

Plants

Asexual reproduction in plants can take a number of forms. Many plants develop underground food-storage organs that later develop into the following year’s plants. Potato plants and daffodil plants do this.

the flower bud is at the centre of the bulb, and a lateral bud is at the side

Daffodil bulb at start of season

remains of leaves are now where the flower bud was, and a new plant has begun to grow from the lateral bud

Daffodil bulb at end of season

Strawberry plant with runners - stems growing sideways

Some plants produce side branches with plantlets on them. The Busy Lizzie plant does this. Others, such as strawberry plants, produce runners with plantlets on them.

Animals

Asexual reproduction in animals is less common than sexual reproduction but it does happen in sea anemones and starfish, for example.

Natural cloning

Twins are genetically identical because they are formed after one egg cell is fertilised but splits to form two embryos. They have the same genes. As the genes came from both parents they are not clones of either parent, but they are natural clones of each other.

Artificial cloning

It is possible to make clones artificially. The cloning of animals has many important commercial implications. It allows an individual animal that has desirable features, such as a cow that produces a lot of milk, to be duplicated several times.

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