Transcript Selective breedingx

Selective Breeding
Explain using an appropriate example from agriculture
why selective breeding has been practiced
Selective breeding improves quality and yield of production from
farm animals and crops. It involves crossing varieties to:
Combine favorable characteristics and allow better productivity,
called hybrid vigour.
Can produce better nutritional value
Gain resistance to disease
Show tolerance to drought and cold
For example, Hereford cattle selectively bred with Brahman cattle
to produce Brahfords that have heat and tick resistance and good
growth rates and foraging skills.
Analyse and present information from secondary sources to trace
the history of the selective breeding of one species for agricultural
purposes and use available evidence to describe the series of changes
thathave occurred in the species as a result of this selective breeding
Wheat - 1788
wheat farmed in Australia but can only be grown in
areas with abundant rainfall and favourable soil
Australia’s poor soil and uncertain rainfall – insufficient
crop yield
diseases such as stem rust would further destroy the
crops
Wheat - 1889
Farrer began a wheat breeding program using varieties from all
over the world
characteristics he sought to breed were rust resistance, early
ripening and good bread-making properties(high gluten levels)
wheat strains from India gave best early ripening characteristics
and also had short stems and more grainsper wheat stalk
Farrer released his ‘Federation Wheat’ in 1902 which matured
early and escaped rust - damage and had high yield
soon, most wheat grown in Australia was Federation Wheat
and it was able to withstand dry climate andharsh heat of
Australia
Fine wool merinos
Over the past 300 years, farmers have selectively bred fine wool
merinos. In doing so, they selected merino rams with favourable
characteristics to sire offspring that will inherit these favourable
characteristics. The aim of selectively breeding merinos is to
produce tougher animals that produce wool of a higher quality
and quantity.
Over the past 300 years:
fibre strength increased
fibre diameter and length decreased
coat density increased
animal hardiness increased
Describe what is meant by ‘gene cloning’ and give
examples of the uses of gene cloning
Gene cloning: The process of selecting a particular gene, cutting it out of the
DNA and inserting it into anotherorganism where copies are made.
1.
A gene is cut out of the chromosome using restriction enzymes. ‘Sticky ends’
are formed where cuts are made.
2.
Circular DNA (plasmid) from a bacteria and cut using the same restriction
enzyme3
3.
The gene is mixed with the bacteria plasmid and DNA ligase is used as a ‘glue’
to allow the gene and plasmid to recombine at matching sticky ends4
4.
Plasmids are reinserted back into bacteria by adding calcium chloride to
increase permeability of bacteria membrane
5.
Bacteria reproduces and plasmids are cloned, cloning the recombinant genes
6.
The bacteria will also express the protein now introduced into its genome
Applications of recombinant genes
production of human insulin to treat diabetics
(e.g. putting gene for insulin into E.coli)
production of human growth hormone to treat
stunted growth
production of proteins that dissolve blood clots
to treat heart attacks and other heart problems
production of bacteria that can break down
toxic wastes from oil spills
Describe the processes used in the cloning of an animal and analyse
the methodology to identify ways inwhich scientists could verify
that the animal produced was a clone
The process by which animals are cloned is called Somatic Cell
Nuclear Transfer (SCNT)
Nucleus from a body cell (somatic cell) of an organism to be
cloned is taken and starved of nutrients soit does not divide.
An egg cell is taken from another animal of the same species and
the nucleus is removed.
The somatic cell is inserted into the egg cell and an electrical
stimulus is used to fuse them and stimulate cell division.
At a certain stage in cell division, the embryo is implanted into a
female surrogate mother.
Techniques to identify a clone:
DNA hybridisation can be used to tell whether two
organisms are genetically identical with strands of each
organisms DNA separated by heat and then one strand
from each put together. Single strands matching up
indicated a clone.
Fingerprinting and profiling looking at bands can be
used to match DNA of two organisms
The original and the clone organism can be determined
using mitochondrial and chloroplast DNA which will
not be the same in each organism, despite cloning.
Discuss a use of cloning in animals or
plants that has possible benefits to humans
Uses:
Cloning plants for agriculture using tissue cultures
Tissue cultures are a way of cloning plants where a
tissue sample (from the meristematic tissue) is taken
and grown in a suitable environment such as soil or an
agar plate.
Benefits include:
Preserving biodiversity for future generations by cloning
endangered species
Cloning newly discovered or genetically engineered species
to better propagate and spread superiorcrops, e.g. BT
cotton
Increasing natural resources, e.g. cloning trees for furniture
Genetically identical plants will produce a uniform product
which is more desirable for consumers, e.g.same colour on
oranges
Less costly and time consuming then continually selective
breeding
Disadvantages lie in the fact that genetic
diversity is decreased.
If there is a selective pressure such as a diseaseor
pest there may be no plants with resistance and
so the whole population could be easily wiped
out.