Plant and animal breeding
A. Artificial Selection and Breeding for Selected Traits
B. Cloning of (Transgenic) Plants and Animals
A.
Artificial Selection
1. A and Breeding (Ref:http://www.pbs.org/wgbh/evolution/library/glossary/glossary.html)
Artificial selection is the selection of plants (crops) or animals for the specific desirable traits by human through
carefully plannedrbreeding to ensure that future generations have those specific desirable traits.
t
It leads to a change
i of gene frequency within a population and give rise to new breed, strains and variants.
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Aims of plant or
i animal breeding
- to produce new
c breeds /varieties
-- via --- artificially induction of polyploidy
i
--- artificial induction of mutants
a
--- controlled
crossing (outbreeding / hybridization)

-
wild plants
l and animals can be modified to have desirable characters (to fit the need of people) and as
domesticated or agricultural species
S
to preserve desirable species (inbreeding)
e
as the experimental
technique for studying evolution
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Importance of artificial
selection
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(a) Increasing food production by developing new varieties of food crops (e.g. wheat, barley, maize, and rice)
c
which are of high yield, greater resistance to disease, greater tolerance to adverse weather conditions etc.)
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(b) Desired characteristics
of animals can be developed for particular purposes e.g. viability, milk composition
and yield, fertility,
resistance to disease, meat production etc.
i
o
General steps of Artificial selection (to select desirable traits) in breeding program:
n
Ref: http://www.chicagobotanic.org/research/breeding/traditional.html
Parental selection: choice of suitable parents from natural wild individuals / natural or induced mutants /
natural or induced
polyploidy with even-numbered set of chromosome (or even GM organisms)
a
nexamples of desirable characteristics
- a higher yield (e.g. better flowers and fruits) in a given environment
d
-
be better adapted to a particular type of soil or climate
be resistant to a disease / pest
B- greater ability to withstand moisture variations
r
controlled crossing
e Transfer of gametes manually
[self-pollination or cross-pollination manually (to avoid selfing) / artificial insemination]
e
- inbreeding
d
- outbreeding
i
screening (Artificial
Selection Stress) for desirable varieties for further breeding and evaluation
n e.g unsuitable plants discarded
g
controlled breeding again and again
- cross between progeny of the same parents
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- backcrossing
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change in gene
r frenquency in the domesticated population
S
stable genetically distinct line of pure breeding with the desirable trait
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e.g. - upright growth architecture
- ability to maintain quality though bad weather
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- yield stability over time is evaluated over a multi-year period.
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c
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- desired size, shape, colour, height of the plant
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1. Artificial Selection in Plant breeding
- controlled hand pollination of flowers from selected plants, via
a. Inbreeding
- mating between genetically closely related individuals
- The genetic effect of inbreeding
-- Increase in the number of homozygous genotype (i.e. reduce variability)
-- decrease in heterozygosity.
Other advantages of inbreeding
• Preserves well-adapted genotypes
• Insures seed set in the absence of pollinators
• Single colonizing individual possible
• Successful short-term — "complete inbreeding
means certain extinction"
Drawback of inbreeding
1. Decreases (or maintains) genetic variability
2. Fertility will be reduced on prolonged intensive
inbreeding
3. The vigour of the population is gradually reduced
because there is greater risk of a double harmful
recessive alleles individual arising.
When will inbreeding be used ?
• It is only used for establishing and selecting genetically distinct lines of pure breeding individuals with
particularly desirable characteristics
• E.g. high yield of eggs in poultry
high yield of milk in cattle
high yield of wool in sheep
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b. Outbreeding (hybrid breeding)
- mating between two genetically unrelated individuals
- Outbreeding is particularly useful in plant breeding, also used in commercial
production of meat, eggs and wool.
-
The genetic effect of outbreeding:
-- increase in heterozygosity in successive generation (i.e.
Increased genetic variability because of meiosis and genetic
recombination
--
The hybrids have phenotypes showing characteristics which
are superior to either of the parental stocks (i.e. hybrid
vigour)
e.g. more robust, more fertile, larger in fruit size / no. increased resistance to disease and earlier
maturity)
very often the performance of crossbred animals above the mid-parent mean of the two parent breeds
Hybrid vigour
is the phenomenon often seen in crosses between two pure-bred lines of plants, that the hybrid is more
vigorous that either of its parents, presumably owing to increased heterozygosity.
[ 91-II-1a (iii)]
Hybrid vigour is the unusual performance (e.g. growth, strength, and health) of hybrids from two less
vigorous parents.
This depends on such alleles for vigour are dominant, and distributed between the 2 parents
Increased vigor results from the increased heterozygosity, which arises from gene mixing of the two parents:
As shown above, the heterozygote produced will carry all the dominant alleles.
Other advantages of out breeding
• May have potential adaptation to changing
conditions and thus greater chance of survival
• May allow plant to live under a wider range of
conditions or to grow faster because of greater
tolerance
• Strong evolutionary potential
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Disadvantages of outbreeding
• may destroy well-adapted genotypes because the
offspring (genotypes) from sexual reproduction are
not guaranteed to be viable, as is the case with selfing
• Relies on effective cross-pollination, seed dispersal,
and establishment
• Sometimes the offspring will be sterile (esp. in
animals)
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c. Polyploidy breeding
- treat plant with chemical to induce polyploidy e.g. colchicines
- polyploidy is a condition where an organism with more than two sets of chromosomes or genomes.
[The word "set" is defined as one haploid set of chromosomes.]
- Advantage
: It is common in plant species and they often have some advantage e.g. forming more
robust and larger fruits than diploid ones.
Disadvantage : often sterile
-
Many modern crops have varieties which are polyploids:
Autopolyploidy
- Banana (triploid)
 seedless but infertile
- Potato (tetraploid)
Allopolyploidy
- Common bread wheat (allohexaploids)
 fertile
 bigger, larger and still fertile
A possible way to produce a tetraploid plant
To produce a tetraploid plant, the alkaloid colchicine is applied to the terminal bud of a branch.
- the original mother cell is diploid (2n).
- during anaphase the chromatids separate and
move to opposite ends of the cell.
- Colchicine causes the dissolution
(depolymerization) of protein microtubules
which make up the mitotic spindle in dividing
cells.
- This leaves the cell with twice as many single
chromosomes (four sets rather than two).
- When this cell divides, each of the two daughter cells will have fours sets of chromosomes
All the cells in the developing branch will be tetraploid (4n) with four sets of chromosomes. This includes cells of
the stem, leaves, flowers and fruit.
Gametes (ovum and male nuclei) produced by a flower on this tetraploid branch will be diploid (2n) with two sets
of chromosomes.
[ C.F.: A flower on the normal diploid (2n) branch will produce haploid (n) gametes containing one set of
chromosomes.]
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2. Animal breeding
Aim of animal breeding: - based on the maintenance and improvement of various breeds which have features
particularly suited to the environment, management conditions and end-product requirement of a farm e.g. high
milk production and meat production
Domestication
Method used in animal breeding
(e.g. sheep, goat, cattle, pig, domestic hen)
• (1) selection of parent (male and female)
• (2) make use of artificial insemination
• (3) make use of natural cycle of animal
Artificial insemination
• Used in animals
• A technique to maximize the use of proven (existing) genetic material
• General steps: 1. Collection of semen, dilution
2. Storage for long periods at very low temp.
3. Injection of semen into female animals to cause pregnancy when required. (i.e. in vivo
fertilization)
(P.S. implantation embryo into uterus after in vitro fertilization inside test tube is also possible)
Artificial insemination is most widely used with cattle and cow (for milk production), and pig breeding and any
mammals.
Advantages of artificial insemination
- a male can fertilize many more females
- semen can be stored or even after the animal has died
- semen can be sent over long distance so that genetic materials can be used as widely as possible.
Advantage of pig artificial insemination
• maximum use of high quality pedigree breeding stock to improve the meat quality
• to lower production costs
• to increase the conception rate
• to prevent the spread of disease
• to overcome the problem arising from the difference in size of the boar (male) and the sow (female)
Artificial breeding and animal selection, coupled with
advances in management, have provided us with
year-after-year increases in productivity.
Ref:
http://132.236.38.49/cpdmp/weblets/fundamentals/Production/
MilkPerCow.htm
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B. Cloning
1. Animal cloning
2. Plant cloning
• Cloning is the process in which identical offspring are formed from a single cells
or tissue.
• A clone is a group of genetically identical cells or an individual derived from a
single ancestral cell, tissue or individual by repeated asexual divisions.
Ref: http://robby.nstemp.com/photo2.html
http://www.time.com/time/daily/special/genetics/cloning.html
http://www.countdown.org/end/cloning_02.htm (cloning and genetics)
http://www.stanford.edu/~eclipse9/sts129/cloning/policy.html (human cloning)
http://whyfiles.org/148clone_clash/
http://www.christiananswers.net/q-aig/cloning.html (cloning – right or wrong?)
1. Animal cloning
Purposes of cloning
• For asexual reproduction: creating a new organism from a single cell of an adult. The genes (but not the far
less-important mitochondrial DNA) of the offspring are identical to the parent.
• Embryonic stem cells production (e.g. for therapeutic purpose): creating embryos to supply embryonic stem
cells as a source of spare parts to treat disease.
• For products or tissues / organs from recombinant DNA: changing genes in cells that will be transmitted to
all offspring, was recently used to make pigs that may supply compatible transplant organs for people
•
Why cloning is used in plant and animal breeding ?
To maintain desirable traits in selected plants and animals.
a. asexual reproduction
This can be achieved using cells derived from a microscopic embryo, a fetus, or from an adult
animal. There have now been hundreds of clones produced from skin cells taken from adult sheep,
cattle, goats, pigs and mice.
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The real key to cloning an adult animal is the ability to reprogram the skin cell nucleus and cause it to
begin developing as if it was a newly fertilized egg.
Method for cloning sheep
Cloning requires specialized microsurgery tools and involves five basic steps
1. Enucleation of the recipient egg
2. Transfer of the donor cell into the recipient egg
3. Fusion of the donor cell to the recipient egg (the oocyte and donor cell are normally fused and the
'reconstructed embryo' activated by a short electrical pulse.)
4. Culturing the resulting cloned embryo in the incubator
5. Transferring the developing embryo into the reproductive tract of a surrogate mother
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Information:
DOLLY-the first successfully cloned mammal:
Dolly was shown to be genetically
identical to the Finn Dorsett mammary
cells and not to the blackface ewe,
which clearly demonstrated that she was a
successful clone (it took 276 attempts
before the experiment was successful).
Dolly has since grown and reproduced
several offspring of her own through
normal sexual means. Therefore, Dolly is a
viable, healthy clone
b. Application of embryonic stem cells cloning
clone human embryos to obtain human tissues for curing diseases
Ref : http://cmgm.stanford.edu/biochem118/Stem%20Cell.html
-- Therapeutic cloning might, after all supply islet cells to treat diabetes or dopamine-producing cells to
treat Parkinson's disease
Theoretically, it's possible to sidestep the
problematic cloning by growing embryonic stem
cells from the adult cells, but that's never been done.
Nuclear transfer, or cloning, may
provide a source of stem cells.
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--. The process of human therapeutic cloning is also a theoretic method for making spare body parts.
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c. For products or tissues / organs from recombinant DNA:
changing genes in cells that will be transmitted to all offspring, was recently used to make pigs that may
supply compatible transplant organs for people
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Views on Cloning
--In the debate over cloning there are those that feel that advances gained from cloning outweigh any social
dilemmas.
--There are those that feel that cloning is wrong on a fundamental moral level and would produce scientific and
social problems.
Pros on Cloning
--Cloning will improve the overall quality of science
and life.
--Cloning might produce a greater understanding of the
causes of miscarriages.
--Cloning experience may add to the increased
understanding of genetics.
--Cloning could be used for parents who risk passing a
genetic defect to a child.
--Damage to the nervous system could be treated
through cloning.
--Cloning will allow a woman to have one set of
identical twins.
Cons on Cloning
--Those that do not agree with cloning feel that is an
effort to religious societies.
--Cloning may reduce genetic variability.
--Cloning may cause people to settle for the best
existing animals.
--Cloning is currently an expensive process.
--Any research into human cloning would eventually
need to be tested on humans.
--Cloning might be used to create “prefect human”.
--Cloning might have a detrimental effect on family
relationships.
Voiced objections to cloning as a method of reproduction
1)
2)
3)
4)
5)
6)
The safety of the procedure is unknown.
It will cause harm to humankind.
Everyone has a “right” to a unique identity.
The child will be abused.
Even if no abuse is intended, the child will be harmed psychologically.
It is unnatural. It is meddling in God `s domain.
7) Dolly the Sheep is dead - possibly the world's most famous animal was put to sleep on 14th February 2003 after
developing progressive lung disease. Dolly was cloned from a dead adult sheep using frozen cells and born on 5th July 1996. There
have been many reports that Dolly may have been getting old before her time, developing arthritis and possibly other problems.
Scientists are waiting for the results of a post mortem to try to understand whether Dolly's latest problems were linked to the cloning
technique, which commonly causes severe abnormalities. The big worry is whether teams trying to clone human babies will
accidentally create very sick children. Ref: http://www.globalchange.com/clonenews.htm
8)
9)
10)
11)
How would a parent react to a genetic twin that happened to be an infant?
What would be the legal status of a child with no clear mother?
Who, if anybody, would be the father?
Life begins at conception, therapeutic cloning is not appropriate.
Impacts of cloning on society
--Since the world was introduced to cloning , it has triggered Hollywood movies like Multiplicity.
--Currently the President of the USA declared they are prohibiting Federal funds for cloning research.
--Animal cloning has the ability to create “low fat” cows and pigs.
--Animal cloning will also allow animal breeders to produce cloned herds of “meat”.
From http://www.globalchange.com/clone_index.htm
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2. Plant Cloning
a. Traditional plant cloning
b. Plant biotechnology
Advantages of plant cloning
1. To maintain desirable traits in selected plants
2. A rapid way of propagating plants in a short period of time compared with traditional breeding methods
3. In tissue culture, the propagates are growing in a sterile medium free of bacteria and fungi so that the
propagates are disease-free
4. Produce genetically identical plants from a stock plant and large number of offspring with desirable traits
5. Require relatively little space for culturing the plants compared with growing plants in the field.
a. Traditional plant cloning
Plant part of choice in micropropagation.
--Exhibit the desirable characteristics of mother plant.
--somatic cells from leaves, flowers, internodes; or primordials cells from terminal or axillary buds; or stem
cells from embryos can be used
Micropropagation
--Involves the mass production of plants from small parts in sterile,
controlled environments.
--Also referred to as vitro propagation
Advantages of micropropagation
--The main advantage is small piece of plant can produce hundreds
of new plants that can be identical to the “mother plant”
- Disease free: produced in a sterile culture environment free of contamination from
bacteria and fungi.
--Gives plants a healthier start and a better chance of defense
Procedures of Tissue culture
• Plant tissue culture is a technique for the propagation of plants under controlled laboratory conditions.
• Plant parts are cleaned of all bacteria, fungi and insects and then placed into sterilized test tubes or other
containers with the nutrients necessary for growth of the plant.
• By manipulating plant hormones included in the nutrients, it is possible to encourage shoot growth and
subsequently root growth.
•
Steps:
- Take pieces of specialized roots, breaking them up into
root cells and growing the root cells in a nutrient-rich
culture.
- In culture, the specialized cells become unspecialized
(dedifferentiated) into calluses.
- The calluses can then be stimulated with the appropriate
plant hormones to grow into new
plants that are identical to the original plant from which
the root pieces were taken.
This procedure, called tissue culture propagation, has
been widely used by horticulturists to grow prized
orchids and other rare flowers.
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Example of Cloning by Tissue Culture in plant: African Violet Plant
Major steps:
- leaf is take from plant
- leaf is cleaned
- cut into pieces or explants
- explants are mixed with chemicals that provide nutrients
- ( explant viewed under scanning electron microscope )
- new shoots develop after 6 – 8 weeks
- shoots cut free from explant placed in new chemical mixtures that help root development
- rooted plant transferred to soil. Humidity is kept high until plant can adjust to new environments (i.e.
acclimatization)
- new leaves are developed that can survive in less humid air
- cover of plant and chemical is removed over a 2 week period in order for plant to adapt to everyday
environment.
Plant cloning for:
Horticultural, Agricultural, and Silvacultural Uses
--To ensure an abundant supply of product
--The guarantee of flourishing, healthy results
--Time management
--Money saver
--More attractive appearance
--Stronger plant structures
--Create the “PERFECT PLANT”
Horticultural, Agricultural, and Silva cultural Benefits
--Quality control- the quality of plant that will be produced
--Being aware of the type and quality is beneficial to grower because it saves time, money, and labor
Ref: http://www.saskschools.ca/~stmarypa/grassroots/bio30/plant_cloning/sld016.htm
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b. Plant Biotechnology
--Involves transfer of only one or few desirable genes
--Allows creation of plants with specific beneficial traits and without undesirable traits.
Overview of the GM plant cloning process:
1. Identify a gene of interest
2. Isolate the DNA with interested gene(s)
3. Clone it (copy and amplify it by PCR)
4. Modify it by DNA recombination technology.
5. Insert it into a vector and transfer the gene into crops of interest.
6. Evaluate performance and further plant breeding
7. EPA/FDA approval
8. Consumer Approval!!
Cloning of interested DNA for GM plant in
bacteria:
To clone a piece of DNA:
DNA is cut into fragments using restriction
enzymes that recognize specific sequences of
bases in DNA.
The fragments are pasted into vectors that have
been cut by the same restriction enzyme.
Vectors (e.g., plasmids or viruses) are needed to
transfer and maintain DNA in a host cell.
Collections of clones are called libraries.
GM plant cloning process:
7) EPA/FDA
approval
8) Consumer
Approval!
!
2) DNA with interested
gene is isolated
Beneficial traits being developed:
--Provides abundant healthy food supply
--Provides tastier fruits and vegetables
--Good nutritional value, and lower saturated fats
--Fights insects, disease and weeds
--Protects environment for our future generations
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Supplement to plant and animal breeding
Glossary:
1. Biotechnology : the use of living organisms for human purposes, including a collection of techniques utilizing
cells and biological molecules to make or modify a product or to improve plants and animals.
2. Genetic engineering: changing genetic make-up of an organism using molecular techniques, which includes
introducing genes from unrelated organisms.
Comparison between classical breeding and plant biotechnology or genetic engineering (e.g. rice and soybean)
Classical breeding
It involves crossing different parental (male
and female) plants and screening their
progenies to identify plants with desirable
traits from each parent.
Only related plants can be crossed to
exchange genetic information, not between
rice and soybean.
People have been using such approach for
selecting crops with higher yield and better
quality over hundreds of years.
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Plant biotechnology or genetic
engineering
Using model methods of biotechnology, a
gene that define specific trait can be freely
moved from one cell into another cell in the
laboratory, an entire transgenic plant can
then be regenerated from the cell.
Genes of any living organism can be used in
transformation. Thus a gene from either
soybean or human can be moved into rice.
This is a relatively new technology
developed in the past twenty years aiming to
speed up the crop improvement at the more
precise approach.
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