Genetic Engineering
Polymerase Chain Reaction (PCR) Fig.
16.3 in text
• a technique for quickly cloning a
particular piece of DNA in the test tube
(rather than in living cells like E. coli).
• Very useful if only have small quantities
such as blood or semen.
• Use temperature changes to separate the
DNA strand, add primers, polymerase
and ta-dah... new strand is made.
Gel Electrophoresis and DNA Profiling. Fig
16.2 in text
• Method using electricity to separate fragments of
DNA
– fragments are made by using restriction enzymes
• Large segments of DNA (negatively charged) can’t
move through gel very far while small ones can.
• In agarose gels, fragments of DNA from about 200
to 50,000 bp can be separated
• The results from electrophoresis can be used for
DNA profiling/fingerprinting – using the patterns of
bands of DNA to identify and compare individuals.
– Useful for identifying rapists, criminals,
determine paternity, determine relatives...
Genetic Screening
• The testing of an individual for the
presence or absence of a gene
• Advantages
– fewer children with genetic diseases are born
(a couple doesn’t reproduce or only selects
“good” embryos for implantation)
– confirmation of animal pedigrees
– if genetic diseases can be found early
enough, treatments can be given to prevent
all or some of the symptoms of the disease
• Disadvantages
– frequency of abortion may increase
– harmful psychological effects
– creation of a genetic underclass (refused
jobs, insurance, spouse...)
Genetically Modified Organisms
• organisms that have had genes from a different
organism transferred to them
• examples
– crops resistant to herbicides (but the weeds
are not)
– insulin gene from humans is put in the
plasmid of E. coli which then makes insulin
– a bacterium gene that codes for a protein
called Bt toxin that kills moths that bore
through corn is transferred to the DNA of
corn
• Benefits
– less pest damage
– less land needed for crops
– less use of insecticides
• Harmful effects
– humans/animals my be harmed by toxin
– other non-corn eating insects could be killed
by pollen from the corn
– cross-pollination could spread the toxic gene
to some wild corn that would then have an
advantage over other natural species
Gene Therapy
• the treatment of diseases by
altering the defective genotype of
the organism
• example: SCID (severe
combined immune deficiency)
– screening before birth can
show SCID
– the enzyme ADA that is
necessary to make healthy
lymphocytes is not made
• lymphocytes, a type of white blood cell,
are made from blood forming
precursors, or "stem," cells in the
bone marrow
– the allele that codes for ADA is obtained and
the gene is inserted into a retrovirus
– the retroviruses insert the gene into the stem
cells’ chromosomes
– new stem cells containing working ADA gene
are injected into the person
Clones
• a group of genetically identical organisms or cells
artificially derived from a single parent cell
• ex) Dolly
– cells were taken from a donor sheep and the
nucleus removed
– eggs from another sheep were taken and the
nuclei were removed
– donor cells and nuclei were fused together using
electricity and then developed into embryos
that were implanted into a surrogate mother
– a lamb was born (Dolly) that was genetically
identical to the donor sheep
• ethical issues in humans
– Pros
• happens naturally with twins
• infertile couples might have better chance
of success with cloning of embryos
– Cons
• psychological/identity problems for groups
of genetically identical people
• cells used in cloning have already begun to
age and therefore cloned humans may age
faster
• lead to selection of a super-race of those fit
to be cloned