Genetic Engineering Selective Breeding


14 déc. 2012 (il y a 9 années et 2 mois)

854 vue(s)

Genetic Engineering

Selective Breeding

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

Goal: to pass desired traits to next
generation of organisms

Examples: Dogs, Cats, Farm animals
and Crop plants

Selective Breeding


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

HOPEFULLY, offspring of cross are
HARDIER than either parent

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

Selective Breeding


Continued breeding of
individuals with similar characteristics

Seeking to maintain desired characteristics of
organism are maintained over many


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

First Cousins NOT ALLOWED to marry!

Selective Breeding

Increasing variation

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

Using mutagens to increase variability!

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


accepted in plants; more
than two chromosomal sets

DNA Manipulation

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

Forced to work with inherent variation
in nature

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

DNA extraction

cells are opened and DNA
is separated from other cell parts

Restriction enzymes

proteins that
preferentially cut DNA at a specific nucleotide

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

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

Cell Transformation


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


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

Cell Transformation

2 essential features:

1. Plasmid has DNA sequence serving as
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
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

An electric voltage is applied to the gel

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

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

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

3. Identify functions of different genes and
gene combinations

Reading DNA sequence

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

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

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

Separate fragments via gel

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

Polymerase Chain Reaction


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!

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

Polymerase Chain Reaction

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

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