IGCSE Biology
Section 5: Use of Biological Resources
d. Cloning
1. Micropropagation
Describe the process of micropropagation (tissue culture) in which small pieces of plants
(explants) are grown in vitro using nutrient media.
Ref:
Pg. 73
8.7 “Plants can be propagated asexually – Tissue Culture”
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.
2.
3.
4.
5.
6.
A small amount of parent tissue or a number of cells are taken and
transferred to plates containing sterile nutrient agar jelly,
Auxins are added to stimulate the cells to divide by mitosis
Cells grow rapidly into small masses of tissue (callus)
More growth hormones are added to stimulate the growth of roots and stems
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.
2. Uses of Micropropagation
Understand how micropropagation can be used to produce commercial quantities of identical
plants (clones) with desirable characteristics.
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
3. Cloning Mammals
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.
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.
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
4. Potential Uses of Cloning
Evaluate the potential for using cloned transgenic animals, for example, to produce
commercial quantities of human antibodies or organs for transplantation.
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.