Download Selective breeding

Environmental Biology &
Genetics
Applied Genetics
Selective Breeding (Animals)
Selective breeding is the selection of
individuals, by man, with desirable
characteristics and allowing them to
breed.
Individuals with undesirable
characteristics are not allowed to
breed.
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Selective Breeding (Animals)
Over a number of generations a
significant improvement in the
characteristics can be seen.
 e.g. the milk yield of dairy cattle has
increased about three-fold in the last
century.
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Selective Breeding (Animals)
Many environmental factors which
influenced how a species evolved were
removed when man domesticated or
cultivated them.
 e.g. animals were provided with food.
 Animals were protected from predators.
This allowed them to grow bigger and
faster.
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Selective Breeding (Animals)
Animal
Characteristic Selected
Sheep
Wool quality
Dogs
Appearance, speed, ability
Cattle
Beef, milk yield
Horses
Strength, speed
Pigs
Growth rate
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Selective Breeding (Plants)
Man has also been selectively breeding
plants.
Superior varieties have been selected
for breeding purposes.
This has been achieved in maize plants
(sweet corn).
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Selective Breeding (Plants)
Selected varieties are crossed in a
process called hybridisation.
The offspring, called hybrids, are
fertile and these can then be further
subjected to selective breeding.
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Limitations of Selective Breeding
Selective breeding relies on sexual
reproduction which can cause problems
for plant breeders such as:
 The desired characteristics may not be
present.
 It is a long slow process.
 Fertilisation is not always guaranteed.
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Genetic Engineering
Genetic engineering is the transfer of
DNA from one type of organism to
another.
The first organisms to have this done
successfully were bacteria.
Bacteria have one large chromosome in a
ring and more smaller rings called
plasmids.
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Genetic Engineering
The genes on the chromosomes code for
certain proteins.
A useful gene can be removed from one
organism and inserted into a plasmid,
and the bacterium will now be able to
produce the protein in a different
organism, e.g. human insulin.
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Genetic Engineering
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Advantages of Genetic Engineering
over Selective Breeding
Genetic Engineering
Selective Breeding
Completely different species
can be combined
Only the same or very closely
related species can be bred together
Only desired characteristics
are produced
Some undesirable characteristics can
show up
Only takes one generation to
get desired results
Can take many generations to get
desired results
Large quantities of protein
produced
Limited quantities of protein
produced
Easier to purify
Harder to purify
Less contamination
High risk of contamination
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Disadvantages of Genetic
Engineering
Inserting genes into animals and plants
has proved to be very difficult.
Some complex proteins can only be
made by plants or animals.
Only a few plants have been found that
will accept the plasmids carrying the
foreign gene.
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Disadvantages of Genetic
Engineering
Viruses have been used to insert genes
but viruses can often cause harm to the
cells.
Syringes and projectiles have been used
to insert the genes, but they often
damage the cells, and often the
inserted genes either only work for a
short time or don’t work at all.
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Disadvantages of Genetic
Engineering
Sometimes an inserted gene can alter
the biochemistry of the animal it is
inserted into, and the result is harmful
by-products being released.
These side effects can be very difficult
to detect and may even be longer term.
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Insulin Production
The transferring of genes from one
organism to another has lead to some
very useful products being made.
One excellent example of this is the
production of human insulin.
Insulin is a protein made in the pancreas
which is a chemical messenger called a
hormone.
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Insulin Production
It acts on cells in the liver to convert
excess sugar in the blood to glycogen
which is then stored in the liver.
Glycogen is a large insoluble molecule
which can later be broken down to
release the glucose when the body
needs it.
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Insulin Production
If a person cannot make insulin they
suffer from diabetes and need to inject
insulin.
Before genetic engineering, insulin was
extracted from pigs and cattle, and this
was used in the treatment of diabetes.
Nowadays the insulin is made by
bacteria which have the gene for human
insulin.
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Insulin Production
It is extracted and purified before
being used.
Insulin made in this way is identical to
human insulin and can be produced in
vast quantities.
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Insulin Production
Plasmid extracted
from bacterial cell.
Gene identified
and cut out of
chromosome using
an enzyme.
Gene spliced
into plasmid by
an enzyme.
Plasmid cut
open by an
enzyme.
Altered plasmid inserted
into host bacterium.
Insulin
mass-produced
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Plasmids
duplicate.
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Blood
Many people donate blood.
This blood can be used either as it is, or
split up into its components, and used in
operations.
Blood can, however carry disease.
There is a risk that the HIV virus can
be transmitted.
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Blood
Haemophilia is a blood disorder in which
the blood fails to clot properly.
This is caused by a lack of a blood
clotting protein called factor VIII.
This factor can be produced by genetic
engineering.
Unfortunately this process is extremely
expensive.
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Fighting Disease
The body protects itself from invading
organisms by producing proteins called
antibodies.
The antibodies recognise the foreign
organism and destroy it.
The body can be stimulated to produce
antibodies for particular diseases by
vaccination.
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Fighting Disease
Genetic engineering can produce
proteins which act as vaccines, or even
the antibodies themselves.
These proteins can then be adapted so
that they can be taken orally, resist the
human digestive system and then be
absorbed into the bloodstream.
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Gene Therapy
Gene therapy is the replacement of a
defective gene with a fully functional
gene.
Cystic fibrosis is one of the most
common genetic disorders.
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Gene Therapy
A defective gene is unable to produce a
protein required for normal cell function
and so the linings of the airways and
pancreas become blocked with a very
thick mucus.
This defective gene has been identified
and isolated.
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Gene Therapy
Scientists are currently investigating
ways of inserting the correct gene into
the body cells.
If this can be achieved, cystic fibrosis
could be cured by gene therapy.
Gene therapy is also being investigated
for cancer.
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Gene Therapy
Special genes called ‘suicide genes’ are
placed into the cancer cells.
These genes are only active in cancer
cells – not normal cells.
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Gene Therapy
They code for enzymes that can change
harmless chemicals into toxins, which will then
destroy the cancer cells.
This type of gene therapy is fraught with
difficulties such as:
 It is difficult getting the genes into the cancer
cells.
 Using modified viruses to do this can result in
diseases being inserted.
 In trials there have been some unexplained
deaths.
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Genetically Modified Organisms
These are organisms which have had
genes inserted from another organism.
These organisms are said to be
genetically modified and are important
in the development of new varieties of
animals and plants.
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Genetically Modified Organisms
These organisms are very beneficial in
the search for new cures for diseases.
Genetically modified organisms are also
useful in improving the quality and
quantity of food produced.
It is easier to genetically modify plants
than animals.
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Genetically Modified Organisms
GM Crop
Modification
Benefit
Soya bean
Resistance to
weedkiller
Increased yield
Tomato
Prevent
softening
Stays ripe longer
Oilseed rape
Produce oils
Used in plastics
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Genetically Modified Organisms
Other improvements made to plants
include:





Drought tolerance
Disease resistance
Pest resistance
Easier harvesting
Richer in vitamins
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Future Developments
The rapid expansion and developments
in genetic modification have lead to
public concern about a number of issues:
 The effect on the environment.
 Safety issues.
 Moral and ethical issues of whether this
sort of practice is acceptable.
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Future Developments
There are many other possible
developments using genetic modification
including:
 Developing crop plants and farm animals to
make medicines.
 Developing organisms with organs which
are not rejected on transplantation.
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