The Production of Cloned Mammals (Edexcel IGCSE Biology (Modular))

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

Cloning to Produce Human Proteins

• 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 is bred that contains a foreign gene within its genome

  • This foreign gene causes the animal to produce a useful compound which gets expressed within its milk

• 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