Download Chapter 15 Genetic Engeneering

Genetic Engineering
Biology
Ch.15
Selective Breeding
• Selective breeding allows only those
organisms with desired characteristics to
produce the next generation.
• Nearly all domestic animals and most crop
plants have been produced by selective
breeding.
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Selective Breeding
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http://www.wisdompanelpro.com/view/bin/images/dog_history_tree.jpg
• Humans use selective breeding to pass
desired traits on to the next generation of
organisms.
Selective Breeding
• Hybridization
– the crossing of dissimilar individuals to bring
together the best of both organisms.
– Hybrids, the individuals produced by such
crosses, are often hardier than either of the
parents.
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Selective Breeding
• Inbreeding
– the continued breeding
of individuals with similar
characteristics.
– Inbreeding helps to
ensure that the
characteristics that make
each breed unique will
be preserved.
– Serious genetic
problems can result from
excessive inbreeding.
http://www.geneticstimes.com/Images/German_shepherd.JPG
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Increasing Variation
• Breeders increase the genetic variation in
a population by inducing mutations.
• Mutations occur spontaneously, but
breeders can increase the mutation rate
by using radiation and chemicals.
• Breeders can often produce a few mutants
with desirable characteristics that are not
found in the original population.
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Increasing Variation
• Producing New Kinds of Bacteria
– Introducing mutations has allowed scientists
to develop hundreds of useful bacterial
strains, including bacteria that can clean up oil
spills.
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Increasing Variation
• Producing New Kinds of Plants
– Mutations in some plant cells produce cells
that have double or triple the normal number
of chromosomes.
– This condition, known as polyploidy, produces
new species of plants that are often larger
and stronger than their diploid relatives.
– Polyploidy in animals is usually fatal.
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The Tools of Molecular Biology
• Scientists use their knowledge of the
structure of DNA and its chemical
properties to study and change DNA
molecules.
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The Tools of Molecular Biology
• Scientists use different techniques to:
– extract DNA from cells
– cut DNA into smaller pieces
– identify the sequence of bases in a DNA
molecule
– make unlimited copies of DNA
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The Tools of Molecular Biology
• In genetic engineering, biologists make
changes in the DNA code of a living
organism.
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The Tools of Molecular Biology
• DNA Extraction
– DNA can be extracted from most cells by a
simple chemical procedure.
– The cells are opened and the DNA is
separated from the other cell parts.
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The Tools of Molecular Biology
• Cutting DNA
– Most DNA molecules are too large to be
analyzed, so biologists cut them into smaller
fragments using restriction enzymes.
• Enzymes found in bacteria used to destroy phage
DNA
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The Tools of Molecular Biology
• Each restriction enzyme cuts DNA at a specific
sequence of nucleotides.
The Tools of Molecular Biology
• Separating DNA
– In gel electrophoresis, DNA fragments are placed at one
end of a porous gel, and an electric voltage is applied to
the gel.
– When the power is turned on, the negatively-charged DNA
molecules move toward the positive end of the gel.
BIOLOGY: CONCEPTS AND CONNECTIONS 4th Edition, by Campbell, Reece,
Mitchell, and Taylor, ©2003.
The Tools of Molecular Biology
• DNA Fingerprinting
Dr. Alec Jeffreys
– A method of
developing a
person’s DNA
“profile,” similar to a
fingerprint.
– Pioneered in England
in 1984 by Dr. Alec
Jeffreys
How does it work?
• 99.9% of your DNA is the same as
everyone else’s.
• The 0.1% that differs are a combination of:
– Gene differences (Differences in the genes
themselves)
– Differences in “polymorphic regions” between
the genes on the DNA.
How does it work?
• Certain points between the genes on the
DNA have repeating base sequences.
– For example:
ATTACGCGCGCGCGCGCGCTAGC
– These are called variable number tandem
repeats (VNTRs for short)
How does it work?
• Everyone has VNTRs at the same place in
their DNA, but they are different lengths
for different people.
– For example:
Person 1: ATTACGCGCGCGCGCGCGTAGC
(7 repeats)
Person 2: ATTACGCGCGCGCGTAGC
(5 repeats)
Using the DNA Sequence
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BIOLOGY: CONCEPTS AND CONNECTIONS 4th
Edition, by Campbell, Reece, Mitchell, and Taylor,
©2003.
• These enzymes also make it possible to take a
gene from one organism and attach it to the
DNA of another organism.
• Such DNA molecules are sometimes called
recombinant DNA.
Using the DNA Sequence
• Making Copies
– Polymerase chain reaction (PCR) is a
technique that allows biologists to make
copies of genes.
– A biologist adds short pieces of DNA that are
complementary to portions of the sequence.
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Using the DNA Sequence
5
• DNA is heated to
separate its two
strands, then cooled
to allow the primers to
bind to singlestranded DNA.
• DNA polymerase
starts making copies
of the region between
the primers.
3
Target
sequence
Genomic DNA
Denaturation:
Heat briefly
to separate DNA
strands
Cycle 1
yields
2
molecules
Annealing:
Cool to allow
primers to form
hydrogen bonds
with ends of
target sequence
Extension:
DNA polymerase
adds nucleotides to
the 3 end of each
primer
Cycle 2
yields
4
molecules
Cycle 3
yields 8
molecules;
2 molecules
(in white boxes)
match target
sequence
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3
5
5
3
3
5
Primers
New
nucleotides
• During
transformation, a cell
takes in DNA from
outside the cell. The
external DNA
becomes a
component of the
cell's DNA.
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http://biology200.gsu.edu/houghton/4564%20%2704/figures/lecture%203/transformati
on.jpg
Transforming Bacteria
Transforming Bacteria
• Foreign DNA is first joined to a small,
circular DNA molecule known as a
plasmid.
• Plasmids are found naturally in some
bacteria and have been very useful for
DNA transfer.
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Plasmids
• Short, circular DNA
molecules outside the
chromosome
• Carry genes that are
beneficial but not
essential
• Replicate
independently of
chromosome
en.wikipedia.org/?title=Plasmid
Transforming Bacteria
• The plasmid has a genetic marker—a
gene that makes it possible to distinguish
bacteria that carry the plasmid (and the
foreign DNA) from those that don't.
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Transforming Bacteria
How do you know which cells
have been transformed?
Transforming Plant Cells
• How can you tell if a transformation
experiment has been successful?
• If transformation is successful, the
recombinant DNA is integrated into one of
the chromosomes of the cell.
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Transforming Plant Cells
• In nature, a bacterium
exists that produces
tumors in plant cells.
• Researchers can
inactivate the tumorproducing gene found in
this bacterium and insert
a piece of foreign DNA
into the plasmid.
• The recombinant plasmid
can then be used to infect
plant cells.
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Transforming Plant Cells
• When their cell walls are
removed, plant cells in
culture will sometimes
take up DNA on their
own.
• DNA can also be injected
directly into some cells.
• Cells transformed by
either procedure can be
cultured to produce adult
plants.
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Transforming Animal Cells
• Many egg cells are large enough that DNA can
be directly injected into the nucleus.
• Enzymes may help to insert the foreign DNA into
the chromosomes of the injected cell.
• DNA molecules used for transformation of
animal and plant cells contain marker genes.
http://www.rikenresearch.riken.jp/images/figures/hi_3609.jpg
Transforming Animal Cells
• Gene Therapy
http://library.thinkquest.org/28000/media/genetherapy/l_gene.therapy-ms.gif
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– DNA molecules can
be constructed with
two ends that will
sometimes recombine
with specific
sequences in the host
chromosome.
– The host gene
normally found
between those two
sequences may be
lost or replaced with a
new gene.
Applications of Genetic
Engineering
Transgenic Organisms
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http://www.bio.miami.edu/~cmallery/150/handouts/D.zebra.htm
http://
http://www.bio.miami.edu/~cmallery/150/handouts/c17
x5transgenic-tobacco.jpg
• An organism
described as
transgenic,
contains genes
from other species.
Transgenic Organisms
• Genetic engineering has spurred the
growth of biotechnology.
– Transgenic animals and plants
– The Human Genome Project
– The production of vaccines, cancer drugs, and
pesticides
– Engineered bacteria that can clean up toxic wastes
– Cloning
• Organ replacement
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• Transgenic bacteria
produce important
substances useful for
health and industry.
Transgenic bacteria
have been used to
produce:
– insulin
– growth hormone
– clotting factor
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BIOLOGY: CONCEPTS AND CONNECTIONS 4th Edition, by Campbell, Reece,
Mitchell, and Taylor, ©2003.
Transgenic Organisms
• Transgenic animals have
been used to study genes
and to improve the food
supply.
• Mice have been produced
with human genes that
make their immune
systems act similarly to
those of humans. This
allows scientists to study
the effects of diseases on
the human immune
system.
http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=cmed&part=A9538
Transgenic Organisms
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Transgenic Animals
• Nils Lonberg, director at
Medarex, bred two
genetically modified mice,
creating a mouse with a
humanized immune
system.
• In response to diseasecausing agents, these
mice make human
antibodies in their cells,
some of which might be
developed into drugs.
http://images.businessweek.com/ss/06/01/critters/source/4.htm
Transgenic Organisms
• Researchers are trying to produce
transgenic chickens that will be resistant to
the bacterial infections that can cause food
poisoning.
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http://www.cals.ncsu.edu/agcomm/magazine/spring03/images/transgenic1.jpg
Transgenic Organisms
• Transgenic plants are now an important
part of our food supply.
• Many of these plants contain a gene that
produces a natural insecticide, so plants
don’t have to be sprayed with pesticides.
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• Bt Corn
– Engineering resistant
corn. Following the
insertion of a gene
from the bacteria
Bacillus thuringiensis,
corn becomes
resistant to corn borer
infection. This allows
farmers to use fewer
insecticides
http://www.bio.davidson.edu/people/kabernd/semin
ar/2004/GMevents/LH/cornear.jpg
Transgenic Plants
http://www.scq.ubc.ca/bt-corn-is-it-worth-the-risk/
• “Golden rice” has been genetically modified
to contain beta-carotene
– This rice could help prevent vitamin A
deficiency
Figure 12.18B
Cloning
Dolly and Bonnie
• A clone is a member
of a population of
genetically identical
cells produced from a
single cell.
• In 1997, Ian Wilmut
cloned a sheep called
Dolly.
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Cloning
Cloning
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http://resources.edb.gov.hk/biology/english/images/genetics/panda.gif
• Researchers hope cloning will enable
them to make copies of transgenic animals
and help save endangered species.
Cloning
• Studies suggest that cloned animals may
suffer from a number of genetic defects
and health problems.
– Abnormal gene expression
– “old” DNA
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DNA technology raises important
ethical questions
• Our new genetic knowledge
will affect our lives in
many ways
• The deciphering of the
human genome, in particular,
raises
profound ethical issues
– Many scientists have
counseled that we
must use the
information wisely
Figure 12.21A-C
Could transgenics harm human
health or the environment?
• Genetic engineering involves
some risks
– Possible ecological damage
from pollen transfer between
GM and wild crops
– Pollen from a transgenic variety
of corn that contains a pesticide
may stunt or kill monarch
caterpillars
Figure 12.20A, B