Genetic linkage maps


Dec 14, 2012 (3 years and 10 months ago)



Plant Science

Problem Area

Cellular Biology and



Student Learning Objectives

1. Describe biotechnology and genetic

2. Explain the differences between genetic
engineering and traditional plant breed

3. Explain the steps in engineering a plant.

4. Explain how desirable genes are located.

5. Explain how selected genes are introduced
into a target organism.

6. Explain how genetically engineered crops are

7. Discuss the benefits and risks of


Agronomic trial



DNA probes

DNA sequence map


Field trials

Genetic engineering

Genetic linkage map

Growth chamber



Physical marker map


Terms cont.


Reporter gene

Safety trial

Transgenic organism

Varietal trial


Viral encoding

What are biotechnology and genetic


is simply the use of living organisms
to create or improve something. Today biotechnology is
centered on the modification of living organisms as a
result of our new understanding of genes and DNA. It
includes techniques such as:

1. Genetic engineering

2. DNA analysis

3. Genetic mapping

4. Gene transfer

5. Plant tissue culture

6. Biofermentation

B. Biotechnology is being used with microbes,
plants, and animals to produce beneficial
products and improve species. It is being
applied to many agricultural processes including:

1. Bread making

2. Beer brewing

3. Wine, cheese, and yogurt fermentation

4. Silage fermentation

5. Classical plant breeding

Genetic engineering

is the manipulation of
genes. It is also referred to as recombinant DNA
technology. This involves moving genetic
information from one organism into a different
organism or replacing it in the original organism
in a new combination. These changed
organisms are called transgenic.

transgenic organism

is one that has either
new genetic information incorporated into itself
or a unique recombination of its original DNA.

How is genetic engineering different from
traditional plant breeding?

Genetic engineering (GE) is different from
traditional plant breeding (TPB) in many ways:

A. With TPB, crosses can be made only within
the same species or closely related species.
This limits the genetic material breeders can
work with. With GE, there are fewer limits to the
genetic material a breeder can work with. Genes
can be taken from any living organism including
bacteria or animals and inserted into a plant.

B. When plants are crossed using TPB, nearly 100,000
genes are combined from each plant. This requires
breeders to employ the technique of backcrossing,
rebreeding back to one of the original parents, many
times to get rid of unwanted genes and restore desired
traits. With GE, a single desired gene can be inserted
into a plant.

C. When a cross is made using TPB, the seeds are
collected and the new generation of plants must be
germinated and grown before the results of the cross
can be verified. Using GE, modified plants are grown in
tissue culture and the change is verified.

D. TPB requires up to 14 generations to produce a new
plant. GE will create a new plant in as few as five

What steps are involved in engineering a

The creation of a transgenic organism begins with a
selected gene from a donor organism and the insertion
of that gene into a host organism. Eight major steps are
required to complete this process.

A. A donor which contains the gene that codes for the
desired trait is identified.

B. DNA is removed from this organism’s cells and cut
into fragments.

C. Fragments of DNA are sorted by size using gel
electrophoresis and grouped. The fragment containing
the desired gene is then isolated.

D. The targeted fragment is joined with new
DNA, making it possible to move the desired
gene into the host organism.

E. The altered DNA is moved into the host cells.

F. These transformed cells are grown into a
complete transgenic organism.

G. This transgenic organism is grown and

H. The transgenic organism is reproduced to
assure that the new gene is transferred to the

What methods are used to find a specific
gene within an organism?

Creating a transgenic organism begins with locating
the specific gene that codes for the desired trait.
Genes are specific sequences of DNA contained
among all of the DNA inside an organism’s nucleus.

In most plants and animals, less than ten percent of
the DNA code for genes. A scientist will use a
variety of mapping techniques to find a specific
gene. There are three kinds of gene maps: genetic
linkage maps, physical marker maps, and DNA
sequence maps.

Genetic linkage maps

show where on the
chromosome a target gene may be. It will provide
the general proximity. These linkages are
determined by examining the frequency that
different traits are inherited together.

Physical marker maps

identify the distance
between a marker and the desired gene along the
strand of DNA. Markers are specific molecular
characteristics of the DNA molecule which can be

DNA sequence maps

describe the order of the
bases (ATGC) around and including the target gene
on the DNA strand within the chromosome.

How are selected genes introduced into a
target organism?

A. The desired gene must be cut out of the
donor organism and combined with other DNA
before it can be inserted into the target
organism. This combination is necessary for the
gene to function, replicate, and be inheritable.

This recombined DNA is usually a
, a
replicating closed loop that comes from a
bacterium. Once inside the host cell, the plasmid
can replicate and be passed on to the next

B. The target cell must remain intact after the
transfer or it will not function. These cells must
not be ruptured or they will die. The tough
cellulose cell wall must be penetrated and the
new DNA gently moved through the cell

1. Enzymes can be used to digest the cell wall,
creating an exposed membrane. Temporary holes are
opened in this membrane to allow gene transfer.
Plant cells with no cell wall are called

and are very susceptible to gene transfer.

2. A microorganism that naturally penetrates plant
cells can be used to transfer DNA into the target cell.
This technique leaves the cell wall intact.

C. There are four methods commonly used to transfer genes and
create genetically modified organisms. A technique called viral
encoding does not create a genetically transformed organism but
does result in an organism that produces a foreign protein.

: DNA is physically injected into a cell. A small
glass needle is moved through the cell membrane. After the
needle has penetrated the membrane, the new DNA is simply
injected into the cytoplasm. Transformed cells are grown into
whole plants that exhibit the desired trait, reproduced so the
offspring contains the new gene.

2. Electroporation: Placing a protoplast into an electrically
charged environment can cause the cell membrane to become
permeable to DNA. The technique of

uses an
electric charge to open holes in the cell membrane, allowing
foreign DNA to enter the cell. The transformed cells are grown
and propagated, with the subsequent generations exhibiting the
new trait.

: In this process, DNA is shot into a cell attached to
microscopic metal particles. These particles are fired from a
specially modified .22 caliber gun. The particles move so fast that
they can penetrate the cell membrane without doing permanent
damage to it. Cells that survive this process are transformed and
can be grown and propagated.

4. Vectors: A living organism, such as a virus or bacterium, or a
plasmid which carries new genetic information into a target cell is
. The desirable gene is spliced into the DNA of the vector.
The vector than penetrates the target cell as part of its natural life
cycle and transforms the target cell through this infection.

Viral encoding
: In this process, a virus is used to carry a new
gene into a cell. This gene does not become part of the cell’s
genetic make up and so is not transferred to future generations.
While the cell is alive and infected with this virus, it will produce
the protein the new gene codes for. This technique is useful in
culturing single cell organisms to produce things such as insulin,
antibiotics, and many vaccines.

D. Many techniques have been developed to identify
genetically transformed plants. These include the use of
reporter genes or marker genes, DNA probes, and
immunoassays. These methods can be used to identify
a genetically modified plant at any stage of
development, from seed to mature plant.

1. Reporter genes: These genes are also referred to
as markers or marker genes.
Reporter genes

for an observable trait and are attached to the
desired gene before transfer into the target organism.
If the reporter gene is functioning, then the desired
gene will also function. These markers are selected
for traits that can be verified early in the plant’s

DNA probes
: This is a short piece of single
stranded DNA with
the complimentary code for the desired gene. It is labeled with
radioactivity. If the gene is present, the probe will stick and the
radioactivity will be detected in the transformed cell. If the gene is
not present, the probe will not stick so there will be no radioactivity

: These are capable of detecting the presence of
the actual desired gene without the use of markers or radioactivity.
They accomplish this by identifying the gene product, or protein, that
the desired gene produces. Immunoassays utilize techniques
working with animal immune systems involving antigens and anti

An animal is injected with the target protein. This is registered as an
antigen by the animal’s immune system. The animal produces an
antibody in response to that specific antigen. These antibodies are
used to detect the presence of the desired gene. These antibodies
can be linked to chemicals that change color, so a simple color
change can proclaim the presence of the desired gene product.

Where are transgenic plants tested?

A. Transgenic plants are tested in growth chambers and field

1. The
growth chamber

is a closed environment designed to
control and optimize factors that affect plant growth. This
controlled environment allows researchers to test the new
plants for traits that may harm the environment, speed the
growth rate of the plants, and evaluate the expression of
desired traits.

Field trials

are conducted outside in a controlled, natural
environment using normal production techniques. Evaluation
of these trials involves much data because of the natural
variability of a field. Analysis of collected data must account
for the effects of weather, soil, pests, and any other naturally
occurring variable.

B. Transgenic plants are evaluated in early
stage testing to determine the answers to a
variety of important questions, including:

1. What traits do they express?

2. Can they pollinate other plants, producing
fertile offspring which might spread the new
trait into wild populations?

3. Can the transgenic plants escape to
become weeds?

4. Are they effective for their intended use?

5. Will they produce unintended
consequences to the environment?

C. Field trials are used to test varietal differences,
farming practices, and the safety of transgenic

Varietal trials

compare transformed varieties to
their normal counterpart to determine the
characteristics of the new varieties. These
characteristics may include yield, pesticide
tolerance, and pest resistance.

Agronomic trials

identify the farming practices
that will give the new varieties their best growing
conditions. These can include population, row
spacing, tillage practices, or fertility programs.

Safety trials

are used to assess any possible
risk the transgenic plant may pose. These are
the same risks assessed in growth chamber
trials (pollinating wild relatives, becoming a
weed). But safety trials also include looking at
the potential health effects on animals, including
humans, that will consume these crops, and the
potential for the development of pest resistance
in the case of insecticidal transgenic plants.

What are the theoretical benefits and risks of

A. Environmental benefits include:

1. The reduction of pesticide use

2. Greater survival of beneficial insects

3. Reduced exposure of farm workers to pesticides

4. Increased use of environmentally friendly
herbicides such as glyphosate

5. Reduction of soil erosion

6. Reduced use of nitrogen fertilizer and the
subsequent pollution from nitrates

7. Early detection of disease

B. Global economic benefits include:

1. More predictable yields

2. Greater yields

3. Reduced cost of production due to the use
of fewer inputs

4. New markets for crops with unique traits
such as pharmaceutical properties

5. Improvements to the world food supply
(increased protein content, new tolerance to
environmental extremes, improved nitrogen

6. Increased efficiency in plant breeding

C. Genetically modified foods may offer
the benefits of:

1. Improved protein content

2. Improved flavor

3. Improved shelf life

4. More vitamins

5. Reduction of allergens or natural toxins

6. Improved fat levels

7. Reduced pesticide residue

D. Genetically altered crops raise a number of
environmental concerns including:

1. The development of insect populations resistant to this control

2. Reduced interest in sustainable agricultural practices because of
the existence of more resistant crops

3. Difficulties in controlling weeds due to transgenic herbicide
resistant crops

4. The creation of new cultivars with unknown consequences as a
result of modified crops breeding with wild plants

5. Increased use of certain herbicides with associated
environmental risks inherent to pesticide use

6. The development of disease
resistant plants resulting in more
virulent strains of the targeted pathogen

7. Poisoned wildlife

8. Reduced genetic diversity as producers become more
dependant on a select group of varieties

9. Inaccurate predictions of environmental safety from field trials

E. Economic/global concerns of biotechnology include:

1. Increased shift to more capital
intensive farming and
large farms

2. Increased seed costs

3. Corporate mergers resulting in less competition among
agricultural suppliers

4. Loss of ability among producers to save seed for
subsequent crops

F. The concerns about biotech foods and human health

1. Antibiotic resistance from marker genes

2. Hidden allergens from marker genes

3. Production of new or increased levels of toxins in food

4. Unknown substances occurring in foods


What are biotechnology and genetic engineering?

How is genetic engineering different from traditional
plant breeding?

What steps are involved in engineering a plant?

What methods are used to find a specific gene
within an organism?

How are selected genes introduced into a target

Where are transgenic plants tested?

What are the theoretical benefits and risks of