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Cloning and stem cells

Stem cells

During the development of an embryoembryo: The developing human offspring inside the womb, most of the cells become specialised. They cannot later change to become a different type of cell.

But embryos contain a special type of cell called stem cells. These can grow into any type of cell found in the body. They are not specialised. Stem cells can be removed from human embryos that are a few days old, for example, from unused embryos left over from fertility treatment.


You may wish to view this BBC News item from 2007 about a British research team that grew human heart valves from stem cells for the first time.

Here are some of the things stem cells could be used for:

  • making new brain cells to treat people with Parkinson’s disease
  • rebuilding bones and cartilage
  • repairing damaged immune systems
  • making replacement heart valves

Therapeutic cloning

If you were to receive medical treatment with cells grown from stem cells, your body’s immune system would recognise the cells as foreign, and they would be rejected and die. But this would not happen if you received cells with the same genes as you.

This could be done by cloning one of your cells to produce an embryoembryo: The developing human offspring inside the womb, then taking stem cells from this. This is called therapeutic cloning. Here are the steps involved:

  1. nucleus [nucleus: Controls what happens inside the cell. Chromosomes are structures found in the nucleus of most cells. ] taken out of a human egg cell
  2. nucleus from a patient's cell put into the egg cell
  3. egg cell stimulated to develop into an embryo
  4. stem cells taken from the embryo
  5. stem cells grown in a container of warm nutrients
  6. stem cells treated to develop into required cell types

Ideas about science - weighing up arguments

The cloning of human embryos is a very contentious issue. You need to be able to use your Ideas about Science to:

  • Say clearly what the issues are. For example, some human embryos will be destroyed during the cloning process.
  • Summarise different views that might be held. For instance, some people think that this is murder. Others believe it is furthering our knowledge of science for the benefit of everyone.
  • Identify and develop arguments based on the idea that the right decision is the one that has the best outcome for the majority of people. For example, even though a few embryos will be destroyed, many people will be free from suffering and cured of diseases that are currently incurable.
  • Identify and develop arguments based on the idea that certain actions can never be justified because they are unnatural and wrong. For example, some people think that, no matter what the benefits are of curing a disease, we should not clone embryos because destroying human life is always wrong.

Remember that these types of decisions are values, and produce questions that cannot be answered by science.

Read on if you are taking the higher paper.

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