The Production of Cloned Mammals (Edexcel IGCSE Biology)

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

Benefits of cloning	Risks of cloning
Cloning can be used to help preserve endangered species or resurrect extinct animals	Cloning results in a lack of genetic diversity. This can make clones more vulnerable to disease or changes in the environment, leaving the population at risk
Cloning makes it possible to quickly and cheaply produce commercial quantities of consistently high-quality plants at any time of the year	There is some evidence that cloned animals may not be as healthy as normal ones
Cloning allows farmers to increase yields by using high-quality livestock and plants	There are ethical concerns about cloning, especially when it comes to humans. Many people believe it is unethical to clone humans. Additionally, cloning in humans has a high rate of failure, with some unsuccessful attempts resulting in stillborn children or children with severe disabilities

• 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