Download Section 13-2

Interest Grabber
Section 13-1
A New Breed
The tomatoes in your salad and the dog in your backyard are a result of
selective breeding. Over thousands of years, humans have developed
breeds of animals and plants that have desirable characteristics. How do
breeders predict the results of crossing individuals with different traits?
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Interest Grabber continued
Section 13-1
1. Think of two very different breeds of dogs that are familiar to you. On a
sheet of paper, construct a table that has the following three heads: the
name of each of the two dog breeds, and “Cross-Breed.”
2. The rows of the table should be labeled with characteristics found in both
breeds of dogs. Examples might include size, color, type of coat,
intelligence, aggression, and so on.
3. Fill in the column for each of the two dog breeds. In the column labeled
“Cross-Breed,” write in the characteristic you would expect to see in a
cross between the two breeds you have selected.
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Interest Grabber
A New Breed
1. Students should refer only to breeds with which they are familiar.
2. Additional traits might include shape of ears, shape of muzzle (pointed or
square), or length of legs with respect to body.
3. Students will likely assume that traits of the cross-breed are intermediate
between those of the two parent breeds.
Section Outline
Section 13-1
13–1
Changing the Living World
A. Selective Breeding
1. Hybridization
2. Inbreeding
B. Increasing Variation
1. Producing New Kinds of Bacteria
2. Producing New Kinds of Plants
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Selective breeding – method of improving a species by
allowing only those individual organisms with desired
characteristics to produce the next generation (applies to
nearly all domestic animals and most crop plants)
•Hybridization – breeding technique that involves
crossing dissimilar individuals to bring together the best
of both organisms
•Inbreeding – continued breeding of individuals with
similar characteristics
Concept Map
Section 13-1
Selective
Breeding
consists of
Inbreeding
Hybridization
which crosses
which crosses
Similar
organisms
Dissimilar
organisms
Organism
breed A
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for
example
for
example
Organism
breed B
Organism
breed A
which
which
Retains desired
characteristics
Combines desired
characteristics
Increasing Variation
•Mutation – inheritable changes in DNA; breeders can
increase the mutation rate by using radiation and
chemicals (oil-eating bacteria)
•Polyploid – condition of having many sets of
chromosomes; usually fatal in animals; plant breeders
use drugs that prevent chromosomal separation during
meiosis (bananas, citrus fruits, day lilies)
Interest Grabber
Section 13-2
The Smallest Scissors in the World
Have you ever used your word processor’s Search function? You can
specify a sequence of letters, whether it is a sentence, a word, or
nonsense, and the program scrolls rapidly through your document,
finding every occurrence of that sequence. How might such a function
be helpful to a molecular biologist who needs to “search” DNA for the
right place to divide it into pieces?
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Interest Grabber continued
Section 13-2
1. Copy the following series of DNA nucleotides onto a sheet of paper.
GTACTAGGTTAACTGTACTATCGTTAACGTAAGCTACGTTAACCTA
2. Look carefully at the series, and find this sequence of letters:
GTTAAC. It may appear more than once.
3. When you find it, divide the sequence in half with a mark of your
pencil. You will divide it between the T and the A. This produces short
segments of DNA. How many occurrences of the sequence GTTAAC
can you find?
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The Smallest Scissors in the World
1–2. Remind students to check their copies for accuracy before they begin the
next step.
3. Students should find three occurrences of the sequence:
GTACTAGGTTAACTGTACTATCGTTAACGTAAGCTACGTTAACCTA
Section Outline
Section 13-2
13–2
Manipulating DNA
A. The Tools of Molecular Biology
1. DNA Extraction
2. Cutting DNA
3. Separating DNA
B. Using the DNA Sequence
1. Reading the Sequence
2. Cutting and Pasting
3. Making Copies
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Words to Know
Genetic engineering – making changes in the DNA code
of a living organism
1. DNA Extraction – cells are opened and the DNA is
separated from the other cell parts
2. Cutting DNA – restriction enzyme cuts a DNA
sequence
3. Separating DNA – DNA fragments are separated and
analyzed (gel electrophoresis)
Restriction Enzymes
•DNA molecules from most organisms are much too
large to be analyzed, so biologists cut them precisely
into smaller segments using restriction enzymes
•Hundreds are known
•Each one cuts DNA at a specific sequence of
nucleotides
•Example: EcoRI finds the sequence CTTAAG on DNA
Restriction Enzymes
Section 13-2
Recognition sequences
DNA sequence
Restriction enzyme
EcoRI cuts the DNA
into fragments.
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Sticky end
Restriction Enzymes
Section 13-2
Recognition sequences
DNA sequence
Restriction enzyme
EcoRI cuts the DNA
into fragments.
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Sticky end
Gel Electrophoresis
•DNA is separated and analyzed
•Used to compare genomes of different organisms or
different individuals
•Used to identify one particular gene out of millions of
genes in an individual’s genome
Gel Electrophoresis
DNA is separated and analyzed
1. A mixture of DNA fragments is placed at one end of a
porous gel
2. An electric voltage is applied to the gel
3. When the power is turned on, DNA molecules, which
are negatively charged, move toward the positive end
of the gel
4. The smaller the DNA fragment, the faster it moves
(It will be located at the end of gel.)
Figure 13-6 Gel Electrophoresis
Section 13-2
Power
source
DNA plus restriction
enzyme
Longer
fragments
Shorter
fragments
Mixture of DNA
fragments
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Gel
DNA Sequencing
•A complementary DNA strand is made using a small
proportion of fluorescently labeled nucleotides
•Each time a labeled nucleotide is added, it stops the
process of replication
•This produces a short color-coded DNA fragment
•When the mixture of fragments is separated on a gel,
the DNA sequence can be read directly from the gel
•The pattern of colored bands tells the exact sequence
of bases in the DNA
Figure 13-7 DNA Sequencing
Section 13-2
Fluorescent
dye
Single strand
of DNA
Strand broken
after A
Power
source
Strand broken
after C
Strand broken
after G
Strand broken
after T
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Gel
Recombinant DNA
•Lab machines known as DNA synthesizers can
assemble short sequences of DNA
•“Synthetic” sequences can then be joined to “natural”
ones using enzymes that splice DNA together
•The same enzymes make it possible to take a gene
from one organism and attach it to the DNA of another
organism
•Such DNA molecules are called recombinant DNA
because they are produced by combining DNA from
different sources
Polymerase Chain Reaction (PCR)
Making copies of a particular gene
1. At one end of the piece of DNA, the biologist adds a
short piece of DNA that is complementary to a portion
of the sequence
2. At the other end, the biologist adds another short
piece of complementary DNA
These short pieces are known as “primers” because
they provide a place for the DNA polymerase to start
working.
PCR (cont’d.)
3. The DNA is heated to separate its two strands, then
cooled to allow the primers to bind to the singlestranded DNA
4. DNA polymerase starts making copies of the region
between the two primers
5. The copies serve as templates, so a few dozen
cycles of replication can produce millions of copies
6. Invented by American, Kary Mulllis
7. The polymerase enzyme was found in bacteria living
in the hot springs of Yellowstone National Park
Figure 13-8 PCR
Section 13-2
DNA polymerase adds
complementary strand
DNA heated to
separate strands
DNA fragment
to be copied
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PCR
cycles 1
2
3
4
5 etc.
DNA
copies 1
2
4
8
16 etc.
Interest Grabber
Section 13-3
Sneaking In
You probably have heard of computer viruses. Once inside a
computer, these programs follow their original instructions and
override instructions already in the host computer. Scientists use
small “packages” of DNA to sneak a new gene into a cell, much as a
computer virus sneaks into a computer.
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Interest Grabber continued
Section 13-3
1. Computer viruses enter a computer attached to some other file.
What are some ways that a file can be added to a computer’s
memory?
2. Why would a person download a virus program?
3. If scientists want to get some DNA into a cell, such as a bacterial
cell, to what sort of molecule might they attach the DNA?
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Sneaking In
1. A file can be downloaded from a diskette, a CD, or
the Internet.
2. The computer user would not willingly download a
virus but would download a program that was useful.
3. Possible answers: a useful protein or a strand of DNA
that the cell would recognize and accept
Section Outline
Section 13-3
13–3 Cell Transformation
A. Transforming Bacteria
B. Transforming Plant Cells
C. Transforming Animal Cells
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Words to Know
Transformation - a cell incorporates DNA from outside
the cell into its own DNA
Bacteria can be transformed simply by placing them
in a solution containing DNA molecules (Recall Griffith’s
experiments.)
Plasmid – small circular DNA molecule
One way to make recombinant DNA is to insert a
human gene into bacterial DNA. The new combination
of genes is then returned to the bacterial cell, and the
bacteria can produce the human protein.
Genetic Marker
•A gene that makes it possible to distinguish bacteria
that carry the plasmid and foreign DNA
•Genes for resistance to antibiotics are commonly used
as genetic markers
•Genetic markers are related to transformation because
the DNA of the marker is integrated into one of the cell’s
chromosomes
•Plasmids have genetic markers (They also serve as
bacterial origins of replication.)
Knockout Genes
Section 13-3
Recombinant DNA
Flanking sequences
match host
Host Cell DNA
Target gene
Recombinant DNA replaces
target gene
Modified Host Cell DNA
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Figure 13-9 Making Recombinant DNA
Section 13-3
Recombinant
DNA
Gene for human
growth hormone
Gene for human
growth hormone
Human Cell
Sticky
ends
DNA
recombination
DNA
insertion
Bacterial Cell
Bacterial
chromosome
Plasmid
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Bacterial cell for
containing gene for
human growth hormone
Figure 13-10 Plant Cell
Transformation
Section 13-3
Agrobacterium
tumefaciens
Gene to be
transferred
Cellular
DNA
Recombinant
plasmid
Inside plant cell,
Agrobacterium inserts part of
its DNA into host cell
chromosome
Plant cell colonies
Transformed bacteria introduce
plasmids into plant cells
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Complete plant is
generated from
transformed cell
Interest Grabber
Section 13-4
The Good With the Bad
The manipulation of DNA allows scientists to do
some interesting things. Scientists have developed
many transgenic organisms, which are organisms
that contain genes from other organisms. Recently,
scientists have removed a gene for green fluorescent
protein from a jellyfish and tried to insert it into a
monkey.
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Interest Grabber continued
Section 13-4
1. Transgenic animals are often used in research.
What might be the benefit to medical research of a
mouse whose immune system is genetically
altered to mimic some aspect of the human
immune system?
2. Transgenic plants and animals may have
increased value as food sources. What might
happen to native species if transgenic animals or
plants were released into the wild?
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The Good With the Bad
1. Students may say that a mouse with a humanlike
immune system would be a good laboratory model
for immune research.
2. Transgenic organisms might disrupt normal balances
in ecosystems and could breed with natural
populations, changing them.
Section Outline
Section 13-4
13–4 Applications of Genetic Engineering
A.Transgenic Organisms
1. Transgenic Microorganisms
2. Transgenic Animals
3. Transgenic Plants
B.Cloning
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Transgenic Microorganisms
1. Bacteria reproduce rapidly and are easy to grow
2. Human forms of proteins such as insulin, growth
hormone, and clotting factor are now produced by
transgenic bacteria
3. In the future, transgenic microorganisms may be
used to fight cancer and develop the raw materials
for plastics and synthetic fibers
Flowchart
Section 13-4
Cloning
A body cell is taken from a donor animal.
An egg cell is taken from a donor animal.
The nucleus is removed from the egg.
The body cell and egg are fused by electric shock.
The fused cell begins dividing, becoming an embryo.
The embryo is implanted into the uterus of a foster mother.
The embryo develops into a cloned animal.
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Figure 13-13 Cloning of the First
Mammal
Section 13-4
A donor cell is taken from
a sheep’s udder.
Donor
Nucleus
These two cells are fused
using an electric shock.
Fused Cell
Egg Cell
The nucleus of the
egg cell is removed.
An egg cell is taken
from an adult
female sheep.
Embryo
Cloned Lamb
The embryo
develops normally
into a lamb—Dolly
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The fused cell
begins dividing
normally.
Foster
Mother
The embryo is placed
in the uterus of a foster
mother.