Genetic Engineering Selective Breeding

Genetic Engineering

Selective Breeding

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Choosing animals/organisms with
desired characteristics to breed and
produce offspring

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Goal: to pass desired traits to next
generation of organisms

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Examples: Dogs, Cats, Farm animals
and Crop plants

Selective Breeding

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Hybridization
-

Crossing dissimilar
individuals to bring together the BEST
traits of BOTH organisms

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HOPEFULLY, offspring of cross are
HARDIER than either parent

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Example: in Crop plants combine
disease resistant of one with food
-
producing capacity of another

Selective Breeding

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Inbreeding
-

Continued breeding of
individuals with similar characteristics

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Seeking to maintain desired characteristics of
organism are maintained over many
generations

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Risk
-

Since members of breed genetically
similar; may increase chances of recessive
disease being expressed

•
First Cousins NOT ALLOWED to marry!

Selective Breeding

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Increasing variation
-

breeders do so by
DELIBERATELY inducing mutations
(ultimate source of genetic variability)

•
Using mutagens to increase variability!

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Examples: new bacterial strains (clean
up oil
-
WOW) or new kinds of flowers

•
Polyploidy
-

accepted in plants; more
than two chromosomal sets

DNA Manipulation

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Until very recently, plant and animal
breeders were unable to modify the
genetic code of organisms

•
Forced to work with inherent variation
in nature

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Even with addition of variation via
mutations, changes in DNA produced
were random and unpredictable

DNA Manipulation

•
TODAY, scientists can use their
knowledge of DNA structure and its
chemical properties to alter the
sequence of DNA

•
Techniques include: DNA extraction, cut
DNA into smaller pieces, identify DNA
sequence one base at a time as well as
make unlimited copies of DNA

Genetic Engineering

•
Genetic Engineering
-

making changes in the
DNA code of a living organism

–
1.
DNA extraction
-

cells are opened and DNA
is separated from other cell parts

–
2.
Restriction enzymes
-

proteins that
preferentially cut DNA at a specific nucleotide
sequence

–
3.
Gel electrophoresis
-

Load DNA onto an end
of a porous gel and apply an electric charge,
separating DNA fragments based on size

Recombinant DNA

•
Combining DNA from different
organisms/different sources

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Using SAME restriction enzyme (cut and
paste), take a gene from one organism
and attach it to the DNA of another
organism

Cell Transformation

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Transformation
-

A cell takes in DNA
from outside the cell. This external DNA
becomes part of the cell’s DNA

•
Plasmid
-

Foreign/transforming DNA
added to a small, circular DNA molecule

Cell Transformation

•
2 essential features:

–
1. Plasmid has DNA sequence serving as
an
origin of replication
; if plasmid gets
inside bacterial cell, sequence ensures
plasmid that it will be replicated

–
2. Contains
genetic marker
-

allows one
to distinguish bacteria
containing/transformed by plasmid vs.
those that have not
-
Antibiotic
resistence gene

Transforming Plant cells

Gel electrophoresis

•
After restriction digestion, a mixture of
DNA fragments (different sizes) is
loaded onto one end of a gelatin
material

•
An electric voltage is applied to the gel

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DNA molecules (negatively charged
-
WHY?) move toward the positive end of
gel

Gel electrophoresis

•
The smaller the DNA fragment, the
faster (and further on the gel) it moves

•
Gel electrophoresis used to:

–
compare DNA sequences of different
organisms or different individuals within
species

–
Locate and identify one particular gene out
of millions of genes in individual’s genome

Using DNA sequence

•
Knowing organism’s DNA sequence, one
can do the following:

–
1. Study specific genes

–
2. Compare genes to other organisms
genes

–
3. Identify functions of different genes and
gene combinations

Reading DNA sequence

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Small, single stranded DNA pieces placed
in test tube with DNA polymerase

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A supply of all four “free” nucleotide bases
is then added, along with one “labeled”
base (label with fluorescent dye)

•
When DNA polymerase adds labeled base,
replication is terminated

Reading DNA sequence

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When using all 4 “labeled” bases
-
each
with different fluorescent color
-
a series
of tiny DNA fragments is created

•
Separate fragments via gel
electrophoresis

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Pattern of colored bands tells exact
sequence of bases in the DNA

Polymerase Chain Reaction

•
PCR
-

Making multiple copies of a
specific gene of interest; a photocopy
machine stuck on “print.”

–
1. At each end of DNA “gene of interest” is
placed a COMPLEMENTARY DNA sequence
(known as a “primer” priming DNA
replication; Start point of DNA polymerase!

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2. DNA heated to high temperature to
separate two template strands

Polymerase Chain Reaction

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3. Next, DNA solution is cooled, allowing
primers to ANNEAL to template strands
(single stranded DNA)

–
4. DNA polymerase starts making copies of
region between primers

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5. NOW, primers themselves can then
serve as templates to AMPLIFY “gene of
interest” that lies between primer
sequences