Edexcel IGCSE Biology 复习笔记 5.4.2 Cloning Mammals

Embryo cloning

• It is possible to clone animals using embryo transplants
• For example, if a farmer wants the best cattle, they must first create an offspring from the best bull and best cow, and then clone this offspring to create many genetically identical copies (clones)
• This process is known as embryo cloning and is achieved in the following way:
  • Egg cells from the best cow are artificially fertilised using sperm cells taken from the best bull
  • This forms an embryo
  • The developing animal embryo is then split apart many times before the cells of the embryo become specialised
  • This forms many separate embryos that are genetically identical
  • These cloned embryos are then transplanted into host mothers
  • The calves born from these host mothers are all genetically identical

   

Embryo cloning

Adult cell cloning

• Adult cell cloning is achieved in the following way:
  • The nucleus is removed from an unfertilised egg cell
  • The nucleus from an adult body cell, such as a skin cell, is inserted into the egg cell
  • A very small electric shock stimulates the egg cell to divide (by mitosis) to form an embryo
  • These embryo cells contain the same genetic information as the adult skin cell
  • When the embryo has developed into a ball of cells, it is inserted into the womb of an adult female (known as the surrogate mother) to continue its development until birth

   

• This process was used to create the first clone (exact genetic copy) of a mammal in 1996
• Scientists in Scotland successfully cloned an adult female sheep
• The clone was called Dolly

Adult cell cloning: the cloning technique used to produce the first cloned mammal, Dolly the sheep

Benefits & Risks of Cloning Table

• It took scientists 276 attempts to successfully clone a sheep
• Scientists created Dolly the sheep because they were exploring the possibility of producing medicines in the milk of mammals
• A transgenic animal that contains a gene within their genome that causes them to produce a useful compound within their milk is produced
• Once this has been done the animal can be cloned to produce a whole herd or flock, all of which produce the same special milk
• This process is known as pharming
• Pharming has been used to produce:
  • Antibodies for targeting cancer cells in humans
  • Blood clotting factor IX for haemophilia (blood clotting disorder)
  • Alpha-1-antitrypsin for cystic fibrosis sufferers

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