5. Use of Biological Resources
d. Cloning
Pearson Edexcel book – P221 - 224
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.
5.17 describe the process of micropropagation (tissue culture) in which small pieces of plants (explants) are grown in vitro using nutrient media
Cambridge book Ref:
Pg. 73 8.7 “Plants can be propagated asexually – Tissue Culture”
Edexcel Book Reference:
P. 221-222
Tissue culture or micro-propagation is a way of propagating plants very quickly by taking a small number of cells from a 'parent' plant and growing them in a medium rich in nutrients and plant growth hormones.
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
In this way, very large numbers of plants can be grown from a single plant.
5.18 understand how micropropagation can be used to produce commercial quantities of identical plants (clones) with desirable characteristics
Edexcel book reference:
P. 222 under table 20.1
Cloning of plants has many important commercial implications. Successful varieties of plants can be produced commercially on a massive scale in a relatively short space of time, enabling scientists to develop:
fast growing crops that give more than one harvest in a year, or
crops with better disease-resistant qualities.
But tissue culture has disadvantages as well as advantages.
Advantages of tissue culture / Disadvantages of tissue culture /A lot of new plants can be grown in a relatively short time / All plants have same genetic make-up - so will all be vulnerable to same diseases or pests
Little space is needed, and conditions can be precisely controlled / No chance of new beneficial characteristics arising by chance
All new plants inherit the same desirable characteristics / No variation means there is a danger of reducing the gene pool
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
Pearson Edexcel Page 223
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.
Here's how it was done:
1. An egg cell was removed from the ovary of an adult female sheep, 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
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. 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.
Animal cloning has potential uses in both farming and medicine (for protein synthesis, gene therapy and organ donation). But there are disadvantages too.
Advantages of embryo transplanting / Disadvantages of embryo transplanting /Allows screening for defects in gametes / Does not add variety - so no opportunity for natural selection
Makes it possible to choose sex and time of birth / Lack of hybrid vigour - animals potentially vulnerable to disease
Exact copies of the 'best' animal specimens, year after year / Danger of reducing the gene pool
Could be used for saving endangered species from extinction / Some animal welfare concerns - eg about the longevity of cloned animals
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.
Transplantation
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.