Download 6.2.1 cloning student version

6.2.1 Cloning
Learning Outcomes
• Describe the production of natural clones in
plants using the example of vegetative
propagation.
• Describe the production of artificial clones of
plants from tissue culture.
• Discuss the advantages and disadvantages of
plant cloning in agriculture.
Cloning
What?
Where?
Why?
When?
How?
Cloning
A clone is an individual that has the identical genetic makeup of
another individual. Nature has its own ability to produce clones, but
the term cloning is used for human intervention in order to produce
identical individuals with desired characteristics.
Identical twins are natural clones as they develop
from one fertilised egg cell
Potatoes are natural clones as they
develop from one parent plant
Cloning
The aim of cloning by human intervention will produce two
individuals with identical genetic information...
Original parent cell
Genetically identical daughter cells
Advantages and Disadvantages of
Cloning?
Natural Cloning in Plants
• Natural cloning is called vegetative propagation
• Occurs in many species of flowering plants
• Usually involve perennating organs, which enable
plants to survive severe conditions
eg runners in strawberries
bulbs in bluebells, crocus
rhizomes in marram grass
stem tubers in potatoes
root suckers (basal sprouts) in English Elms
Reproductive Cloning
Many plants such as the Buttercup can naturally
reproduce asexually which always produces
clones of the parent plant.
‘Parent’ plant
Roots
Stolon
(runner)
The Buttercup produces stolons (runners) which spread horizontally
over the soil.
Roots and shoots develop from buds on the stolon, and eventually
new independent plants are formed.
Reproductive Cloning
Produces more offspring
eg for agriculture or GM organisms
Vegetative propagation in potatoes
English Elm
• The English Elm only
reproduces by suckering
– The growth of new trees from
the roots or meristem tissue
in the trunks
• As all English Elms are
genetically identical they
are all susceptible to the
fungus, Dutch elm disease
Reproductive Cloning
For centuries, gardeners and horticulturalists have exploited this
ability of many plants to reproduce asexually.
New plants can be grown from older plants by taking cuttings.
The use of stem cuttings can be used as an easy method for
propagating plants such as Geraniums – this is a form of cloning.
1. Cut stem just below leaf joint
4. Water sparingly
2. Remove leaves from lower stem
3. Place cutting in moist compost
5. Cover with plastic bag
Reproductive Cloning
Eventually the cutting produces roots, shoots and new leaves.
It will be a clone as it is genetically identical to its parent.
parent
clone
By using this method a large number of identical plants can be
produced in a short space of time and for minimal cost.
Reproductive Cloning
Leaves can also be used to artificially propagate plants.
Begonia plants can be easily
grown from detached leaves.
1. Carefully remove
a healthy leaf
4. Place the cutting
inside a plastic bag
Begonia plant
2. Turn a leaf upside down and
then cut across the veins
3. Put the leaf right side up onto
moist compost and peg it in place
5. Small plants should
grow from the cuts
(3 months)
Reproductive Cloning
Hollyhocks and Phlox can be simply grown from
pieces of root placed in moist compost.
Hollyhock
Cover top of cutting with soil
Piece of root
Sloping cut at root base
Pot
Phlox
Questions
1. Explain the advantages and disadvantages of
propagating crop plants by cuttings rather
than planting seeds
(4 marks)
2. Suggest why it is important to describe
clones as genetically identical to their parent
rather than simply identical – and why this
may not always be true
(5 marks)
Have a go yourself!
•
•
•
•
•
•
•
Use a non flowering stem
Make a slanting cut in the stem
Dip in hormone rooting powder
Reduce leaves to 2 or 4
Plant in soil (ensure your vessel has sufficient drainage)
Keep cutting well watered
Cover with a plastic bag for a few days
Synoptic Q: rooting powder contains which type of
plant hormones?
Artificial Cloning in Plants
Artificial Vegetative propagation
• It is possible to artificially propagate valuable
plants
– Grafting – a shoot section of a woody stem is
joined to a root stock
– Tissue culture/micropropagation
Grafting
Q: in order for a new plant to be propagated
which cells will need to be isolated?
Modern Cloning Techniques
Plant Tissue Culture
Meristem tissue has the ability to differentiate into any cell type.
If meristem tissue is isolated it can develop into a whole new plant.
First of all a plant is selected with desirable features, e.g. heavy
cropping carrot plant with a good flavour.
Modern Cloning Techniques
Plant Tissue Culture
Then a carrot with the required characteristics is cut into hundreds of
tiny pieces which are sterilised in bleach.
The bleach kills any microbes that may infect the pieces of tissue, but
does not harm the carrot tissue itself.
carrot tissue
on nutrient agar
Each piece of tissue is placed onto nutrient agar jelly (suitable pH)
which has all the nutrients and plant growth hormones needed for
healthy growth. The tissue culture is then incubated at a suitable
temperature.
Modern Cloning Techniques
Plant Tissue Culture
Tissue culture can be used to propagate almost any plant.
The advantages to commercial growers of this method of plant
propagation, far outweigh the disadvantages.
Modern Cloning Techniques
Plant Tissue Culture - Summary
In the right growth conditions
(suitable temperature, pH, growth
substances)
undifferentiated
callus
few
days
carrot tissue
on nutrient agar
carrot tissue
develops into a callus
few
days
young plants
are potted up
magnified view of differentiated
callus with young shoots and
leaves
callus tissue has differentiated
into embryonic shoots, roots and
leaves
differentiated
callus
Micropropagation
Modern Cloning Techniques
Disadvantages of Plant Tissue Culture
Discuss the disadvantages
Cauliflower cloning practical!
Questions
1. Why is it essential that meristem cells are
present in the plant tissues used for any
artificial vegetative reproduction method?
(2 marks)
2. Suggest an advantage of placing a graft on a
tree that produces a particular desirable fruit
on to a rootstock of a different tree species
(2 marks)
Give an example of a natural clone in
animals
Artificial Cloning in Animals
Learning Outcomes
• Outline the differences between reproductive
and non-reproductive cloning.
Cloning in Animals
• Reproductive cloning
– Cloning to produce a
whole organism
– Examples
• Embryo transplantation
• Dolly the sheep
• Non-reproductive
cloning
– Using cloning to produce
cells
– Examples
• Stem cell research
• Production of cells,
tissues or organs
Reproductive cloning in animals
Two methods of artificially cloning animals
– Splitting embryos for embryo transplantation
• All offspring are identical to each other but not to the
surrogate mothers
– Nuclear transfer using enucleated eggs
• Nucleus is taken from a differentiated cell in an adult,
and placed into a enucleated egg cell
Embryo Transplants/Embryo Twinning
In the agricultural industry, yield and productivity in farm animals
is just as important an issue as it is for crop plants.
Animal farmers can increase their productivity by rearing more
animals and increasing their growth rate.
Most importantly, selective breeding allows farmers to rear
superior animals with characteristics such as increased
milk production and faster growth.
Cloning and subsequent embryo transplantation are techniques that
can allow farmers to have hardy, productive stock at a relatively low
cost and within one generation.
Embryo Transplants/Embryo Twinning
Sperm is collected from a superior bull, and a superior, genetically
valuable cow is brought into oestrus by injecting her with the hormone
prostaglandin.
Embryo Transplants/Embryo Twinning
The valuable cow (donor
cow) is now injected with
FSH and LH to stimulate
follicle and egg cell
development.
Egg cells are recovered from
the donor cow and fertilised
in the laboratory (in vitro).
After a few days any resulting
embryos can be screened for
their sex
and any genetic defects.
Some of the recovered embryos may be frozen for future use.
Embryo Transplants/Embryo Twinning
The fertilised egg cells each divide into a ball of cells. At such an
early stage in their development these cells have not yet become
specialised.
This means that each cell within the ball of cells has the potential to
develop into a new fully formed healthy cow.
From one screened embryo (with the desired characteristics) the
cells are separated and each one grows into a new embryo.
Recipient, less valuable cows
are brought into oestrus and
the embryos are transferred –
two embryos are usually
transferred into the uterus of
each cow for twinning.
Embryo Transplants /Embryo Twinning
The embryos will complete their development within the less
valuable cows for the full term of pregnancy and eventual calving.
This procedure protects the valuable cows from the risks of
pregnancy and increases the number of calves born.
This way many superior calves can be
born within one generation –
improving the farmers productivity,
competitiveness and profit figure.
All superior calves born this way are
cloned individuals.
Embryo Transplants /Embryo Twinning - summary
Fusion Cell Cloning /Somatic Cell Transfer
The cloning of animals is generally viewed by gene technologists
as a means to improve a particular breed or variety.
In 1996, scientists at the Roslin
Institute in Scotland created the
much-publicised
‘Dolly’ the sheep.
Ewe A
Ewe B
nucleus
Dolly was created by removing a
nucleus from a mammary gland in
a ewe (ewe A).
enucleated
cell
An unfertilised egg cell from another ewe (ewe B) was taken and its
nucleus was removed. This cell is then described as ‘enucleated’.
Fusion Cell Cloning (SCNT)
The mammary gland nucleus was then introduced into the enucleated
egg cell, and the new cell was given a small electric shock to fuse the
parts together and start the process of cell division (mitosis).
Ewe A
Ewe B
nucleus
enucleated
cell
fusion of nucleus & cell to form zygote
small electric shock to stimulate cell division
zygote starts cell division
Within a few days of keeping the cell in optimum environmental
conditions, the cell started to divide into a ball of cells.
Fusion Cell Cloning(SCNT)
The ball of cells was then
implanted into the uterus of
another female sheep (ewe C).
Ewe A
nucleus
Following the normal gestation
period of 148 days, Dolly was
born.
enucleated
cell
fusion of
nucleus & cell to
form zygote
Dolly was therefore a genetic
clone of the sheep from which the
nucleus was taken (ewe A).
When a clone is produced by
joining a nucleus from one cell
with an enucleated cell from
another, it is called fusion
cloning or adult cell cloning.
Ewe B
zygote divides
and embryo
develops
embryo
implanted into
uterus of black
faced sheep
Ewe C
dolly grew to be
a fully developed
adult
after 148 days
dolly was born
Fusion Cell Cloning(SCNT) - summary
Dolly the Sheep
• Dolly the sheep is
believed to have
suffered from a serious
health problem which
developed at a
relatively early age
Artificial Cloning in animals
• Advantages
• Disadvantages
Moral and ethical Arguments


Non-reproductive cloning in animals
Non-reproductive cloning involves the production of
genetically identical cells which has advantages:
•
•
•
•
Possibilities of non-reproductive cloning
• Potential future uses include
– Regeneration of heart tissue following a heart attack
– Repair of nervous tissue eg in cases of MS
– Repairing the spinal cord
• Stem cells taken from the patient to produce the
tissues mean that tissue rejection by the immune
system is less likely
• Sometimes known as therapeutic cloning
• As always there are ethical issues!