Genetic Engineering
Ch 15
“Real World Biology”
Selective Breeding
Selective Breeding
People select organisms with desired
characteristics to produce next generation
Takes advantage of naturally occurring
variation
Selective breeding of teosinte grass by
native Americans 6000 years ago led to
corn as we now know it
Selective Breeding
Hybridization
Cross dissimilar organisms
to bring together best of
both organisms
Ex: disease resistance +
increased yield
Benefits include hardier
plants
American botanist Luther
Burbank developed more
than 800 varieties of plants
using selective breeding
methods.
Selective Breeding
Inbreeding
Breeding a line of organisms with similar
characteristics
Ex: dog breeds
Risks- decreased genetic variation and
increased susceptibility for certain
diseases/disorders
Ex: hip dysplasia
Increasing Variation
Process used to
increase the variation
normally present in
nature
But why?
 Biotechnology is the
application of a technological
process, invention, or method
to living organisms.
Increasing variation
Can be accomplished through mutations
Mutations are usually random, but can be
induced via radiation and chemical
exposure
Potential to yield few beneficial mutants
with desirable characteristics not found in
original population
Increasing Variation
Bacteria- can treat millions at a time
increasing chances of producing useful
mutants
Ex: oil-digesting bacteria
Increasing Variation
Plants-arresting chromosome separation
during meiosis to produce polyploids
Known to be more vigorous than diploid
relatives
13-2 Manipulating DNA
Mutations are random
Having a way to alter DNA in a very
specific way to achieve a particular result
has huge advantages
Scientists can now use the knowledge of
DNA structure and its chemical properties
to study and change DNA molecules
Tools of Molecular Biologists
Genetic engineering allows biologists to
rewrite the DNA code of an organism
Modern techniques employed can
Extracting DNA from cells
Cutting it into smaller pieces
Identifying sequences of bases in DNA (genes)
Making unlimited copies
Finding Genes
Started with Douglas Prasher (1987)
Prasher wanted to find a specific gene in a jellyfish
that codes for a molecule called green fluorescent
protein, or GFP
• GFP is a natural protein that absorbs energy from light
and makes parts of the jellyfish glow
Prasher thought that GFP from the jellyfish could be
linked to a protein when it was being made in a cell
• bit like attaching a light bulb to that molecule
Finding Genes (GFP specifically)
Prasher compared part of the amino acid sequence of
the GFP protein to a genetic code table
 was able to predict a probable mRNA base sequence that
would code for this sequence of amino acids
Then used a complementary base sequence to “attract”
an mRNA that matched his prediction and would bind to
that sequence by base pairing.
 After screening a genetic “library” with thousands of different
mRNA sequences from the jellyfish, he found one that
bound perfectly
Finding Genes
To find the actual gene that produced GFP,
Prasher took a gel in which restriction
fragments from the jellyfish genome had been
separated and found that one of the fragments
bound tightly to the mRNA
That fragment contained the actual gene for GFP
This method is called Southern blotting, after its
inventor, Edwin Southern.
Finding Genes- Southern Blot
Analysis
Finding Genes
Today it is often quicker and less expensive for
scientists to search for genes in computer
databases where the complete genomes of
many organisms are available.
Copying DNA (specific genes)
 First step is a polymerase chain reaction (PCR)
 Heat a piece of DNA
• separates its two strands
 DNA cools and added primers bind to the single strands
 DNA polymerase starts copying the region between the
primers
• These copies can serve as templates to make still more
copies.
Polymerase Chain Reaction
Once biologists find
a gene, a technique
known as
polymerase chain
reaction (PCR)
allows them to make
many copies of it.
1. A piece of DNA is
heated, which
separates its two
strands.
Polymerase Chain Reaction
2. At each end of the
original piece of DNA, a
biologist adds a short
piece of DNA that
complements a portion
of the sequence.
 These short pieces are
known as primers
because they prepare, or
prime, a place for DNA
polymerase to start
working.
Polymerase Chain Reaction
3. DNA polymerase
copies the region
between the primers.
These copies then serve
as templates to make
more copies.
4. In this way, just a few
dozen cycles of
replication can produce
billions of copies of the
DNA between the
primers.
Copying DNA
It is relatively easy to extract DNA from cells
and tissues.
 The extracted DNA can be cut into fragments
of manageable size using restriction enzymes.
 These restriction fragments can then be
separated according to size, using gel
electrophoresis or another similar technique
Gel Electrophoresis
Recombinant DNA Technology
It is a form of genetic engineering that cleaves
DNA into small fragments and inserts those
fragments into a host organism
Host may be the same or a different species
Transgenic Organisms
Organisms who have incorporated foreign
DNA in their chromosomes and use this
new DNA as their own
How to Produce a Transgenic Organism
Step 1: Isolate the gene in the foreign
DNA that you want to insert
Ex: isolate the gene for beta carotene in a
daffodil so you can then add it to rice
Step 2: Cut it out of the chromosome (in
daffodil) using restriction enzymes.
Restrictions enzymes are bacterial
proteins that have the ability to cut both
strands of the DNA molecule at a specific
nucleotide sequence
Resulting fragments can have blunt ends
or sticky ends
Some Commonly used REs
EcoRI (eco r one)
HindIII (hindi three)
BamHI (bam h one)
TaqI (tack one)
Step 3: Cut host’s DNA with the same RE
so cut ends will match up
When DNA from two different organisms
joins up- recombinant DNA is formed
Vectors
Getting DNA from one organism into
another requires a vector
The vector introduces the new DNA into the
host cell
Bacterial DNA is often used as a vector
Bacterial DNA
Bacteria contains plasmids- small rings of
DNA separate from the bacterium’s larger
circular chromosome
The foreign DNA is inserted into the
plasmid by cleaving both using the same
restriction enzyme
Sticky ends match up and foreign DNA
becomes part of plasmid
Gene Cloning
Plasmid with foreign DNA (Now
considered recombined DNA) is inserted
into a bacterial cell
Plasmids can replicate within the cell and
can produce up to 500 copies in the cell
Soon Tons of Copies!
Bacteria clones the recombinant DNA
Clones-genetically identical copies
How?
Bacterial cells themselves will reproduce
quickly, each with hundreds of copies of
the recombinant DNA inside (plasmid +
foreign DNA)
Introduction into Host Cell
Plasmid is then inserted into a host’s
chromosome where it will be replicated
each time the cell replicates along with the
organism’s other chromosomes
The host cell can transcribe/translate that
recombinant DNA into protein just like all
other proteins coded in its DNA