Genetic Engineering

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10 Δεκ 2012 (πριν από 4 χρόνια και 6 μήνες)

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Genetic Engineering
Chapter 13
Selective Breeding

refers to the process of allowing only those
animals with the desired characteristics to
reproduce.

Nearly all domestic animals are the products of
selective breeding

Ex. Dogs (all the same species)

Do humans use selective breeding?
Hybridization

is the process of crossing two dissimilar
individuals to bring together the best of both
organisms

Typically the more genetically different the
parents the healthier the offspring.
Inbreeding

the process of breeding individuals with like
characteristics to maintain a pedigree

has the disadvantage of making genetic
defects more likely.

Used a lot in dogs
Mutations

We can increase the genetic variation in a
population by causing mutations, which
are the ultimate source of all genetic
variation.
Mutations

mutations can be increased by exposure to
chemicals and radiation

remember most mutations are harmful,
chances are that a few will cause desirable
characteristics that are not found in the
general population.

Oil
-
eating bacteria
Genetic Engineering

refers to making changes in the DNA code of
a living organism

Examples:

SCID mice

Insulin producing bacteria

pGlO
Isolating DNA

Restriction Enzymes
-
cuts DNA

Polymerase Chain Reaction
-
copies fragments

Gel Electrophoresis
-
separates fragments
Restriction Enzymes
Steps of PCR
Steps of PCR

1) Denature DNA
-
heat to 95
°
C

2) Anneal Primers
-
cool to 55
°
C

3) Polymerization
-
72
°
C using
Taq
Polymerase
PCR continued
PCR in Medicine
Since 1987, PCR has had a major impact on pre
-
natal diagnosis of single gene disorders

also very important in carrier testing

improved speed, accuracy and technical flexibility
over previous methods

now possible by PCR in 4
-
7 days vs. 2
-
4 weeks by
Southern blotting
PCR and pre
-
natal
diagnosis
For pre
-
natal diagnosis, PCR used to amplify
DNA from fetal cells obtained from amniotic
fluid
Other conditions which can be detected with
same approach include:
Tay
-
Sachs disease, phenylketonurea, cystic
fibrosis, hemophilia, Huntingdon's disease,
Duchenne muscular dystrophy (DMD)
PCR to detect HIV

PCR detection of HIV genomes may occur before the
appearance of anti
-
HIV antibodies in patient blood

viral DNA/RNA only represents minute proportion of total
cell DNA

Only a small fraction of blood cells are infected (1/10,000)

also require high degree of
specificity
while also targeting
conserved regions of
DNA to guard against high level of
genetic variability characteristic of retroviruses

High risk of cross
-
contaminating sample with small
amounts of amplified DNA from previous sample requires
extra precautions to prevent false
-
positives

PCR can detect 10
-
20 copies of viral DNA from 150,000
human cells
PCR can be more rapid and
accurate than other tests

Diagnosis of the middle ear infection known as otitis
media. The technique has detected bacterial DNA in
children's middle ear fluid, signaling an active infection
even when culture methods failed to detect it.

Lyme disease, the painful joint inflammation caused by
bacteria transmitted through tick bites, can be diagnosed
by detecting the disease organism's DNA contained in
joint fluid.

PCR is the most sensitive and specific test for
Helicobacter pylori
, the disease organism now known to
cause almost all stomach ulcers.

PCR can detect three different sexually transmitted
disease organisms on a single swab (herpes,
papillomaviruses, and chlamydia).
OJ Simpson Murder Trial
The case against
Mr. Simpson was
built in part on
evidence from
polymerase chain
reaction (PCR)
analysis of blood
evidence.
PCR and Forensics
In the OJ Simpson
criminal trial, PCR
analysis of DNA blood
evidence was used to
attempt to prove his
guilt or innocence.
Images from CNN web site: www.cnn.com
PCR and Forensics
In the OJ
Simpson trial, a
statistical
analysis of PCR
markers was
used to argue
that the number
of persons other
than Mr. Simpson
who had these
same markers
was unbelievably
small. This
strategy failed.
PCR in Forensics
Crucial forensic evidence may be present in very small
quantities.

often too little material for direct DNA analysis

but PCR can generate sufficient DNA from a single cell

PCR also possible on extensively degraded DNA

examples include DNA from single dried blood spot, saliva (on
cigarette butt), semen, tissue
from under fingernails, hair root
Other advantages of PCR in forensic science are:

relatively simple to perform and simple to standardize

results obtainable within 24 hours
The major legal problem with PCR is that identification is made
from copied DNA rather than from the original material.
Another potential problem: cross
-
contamination between
samples.
PCR excludes but does not
include
DNA typing is only one of many pieces of evidence that
can lead to a conviction, but it has proved invaluable in
demonstrating innocence.
Dozens of such cases have involved people who have
spent years in jail for crimes they did not commit.
One example is Kirk Bloodsworth. The Maryland
waterman was wrongly imprisoned for almost nine years
for the rape and murder of a 9
-
year
-
old girl, but was freed
in 1993 with the aid of PCR. Even when evidence such as
semen and blood stains is years old, PCR can make
unlimited copies of the tiny amounts of DNA remaining in
the stains for typing, as it did in Bloodsworth's case.
Gel Electrophoresis
Transgenic Organisms

organisms that contain DNA from other
organisms

Insulin
-
producing bacteria

Transgenic animals

mice with human immune genes
Steps in Making Transgenic
Organisms

Use Restriction Enzymes

Produce Recombinant DNA

Insert Recombinant DNA into Organism

Select for Transformed Organism
Cloning

the process of producing an identical
organism from a single cell.

Most commonly used with bacteria

Some use in eukaryotes