5 d) Cloning 5.17 describe the process of micropropagation (tissue culture) in which small pieces of plants (explants) are grown in vitro using nutrient media 5.18 understand how micropropagation can be used to produce commercial quantities of identical plants (clones) with desirable characteristics 5.19 describe the stages in the production of cloned mammals involving the introduction of a diploid nucleus from a mature cell into an enucleated egg cell, illustrated by Dolly the sheep 5.20 evaluate the potential for using cloned transgenic animals, for example to produce commercial quantities of human antibodies or organs for transplantation

You can clone plants in two ways: 5.17 describe the process of micropropagation (tissue culture) in which small pieces of plants (explants) are grown in vitro using nutrient media You can clone plants in two ways: 1. By taking cuttings – but there is a limit to how many plants you can make using this method. 2. Micropropagation – taking tiny amounts of tissue from a plant that are grown in special nutrient media.

Micropropagation This involves taking tiny amounts of tissue from a plant cell (called explants) that are grown in special nutrient media. The plant tissue is supplied with hormones and all the minerals it needs to produce huge numbers of tiny new shoots These are then transferred to a different medium with hormones that cause the growth of roots. The tiny new plants are then transferred to compost in a greenhouse until they become established plants.

This technique involves the following steps: 1. A small amount of parent tissue or a number of cells are taken and 2. transferred to plates containing sterile nutrient agar jelly, 3. Auxins are added to stimulate the cells to divide by mitosis 4. Cells grow rapidly into small masses of tissue (callus) 5. More growth hormones are added to stimulate the growth of roots and stems 6. The tiny plantlets are transferred into potting trays where they develop into plants

Advantages of micropropagation Produces large numbers of genetically identical plants very quickly. Produces species that are hard to grow in other ways. Genetic modifications can be made in a small number of plants which then give thousands of plants carrying the desired change. Tiny plants can be stored until needed. Plants can be produced at any time of the year.

Disadvantages of micropropagation Because all plants are genetically identical they could all be vulnerable to a new disease or a change in conditions.

Cloning of animals is now commonplace in laboratories. 5.19 describe the stages in the production of cloned mammals involving the introduction of a diploid nucleus from a mature cell into an enucleated egg cell, illustrated by Dolly the sheep Cloning of animals is now commonplace in laboratories. The most famous example of animal cloning is Dolly the Sheep, born in the UK in 1996 using a technique called embryo transplanting. Cloning animals is much more difficult than cloning plants, and cloning mammals is the most difficult of all.

Dolly the sheep Here's how it was done: 1. An egg cell was removed from the ovary of an adult female sheep (Sheep B), and the nucleus removed. 2. Using micro-surgical techniques, the empty egg cell was fused with DNA extracted from an udder cell of a donor sheep (Sheep A) 3. The fused cell now began to develop normally, using the donated DNA. 4. Before the dividing cells became specialised the embryo was implanted into the uterus of a foster-mother sheep (Sheep C). The result was Dolly, genetically identical to the donor sheep.

5.20 evaluate the potential for using cloned transgenic animals, for example to produce commercial quantities of human antibodies or organs for transplantation Read page 242…

Human Antibodies Antibodies are obtained from clones of white blood cells. Unfortunately, these cells will not grow in culture and this problem has to be got round by fusing them with cancerous cells. Cancer cells will continue to grow and divide indefinitely, though they do not produce antibodies. The fused cells produced from cancer cells combined with white blood cells will continue to grow and divide (given suitable and adequate nutrients) and they also secrete antibodies.

Why we do it? Once a monoclonal antibody is made, it can be used as a specific probe treat conditions caused by toxins, or poisonous substances, such as snake venom. The body does not make the antibodies quickly enough and so they can be injected to act as an anti venom if someone is bitten by a poisonous snake.

Transplants Patients die every year for lack of a replacement heart, liver, or kidney. For example, about 5,000 organs are needed each year in the United Kingdom alone. Transgenic pigs may provide the transplant organs needed to alleviate the shortfall. Currently, transplantation is difficult due to a pig protein that can cause donor rejection but research is underway to remove the pig protein and replace it with a human protein.