Sequencing of the human genome was completed by 2007
DNA sequencing has depended on advances in technology, starting with making
, nucleotide sequences from two different sources, often two
species, are combined
into the same DNA molecule
DNA technology has launched a revolution in
, the manipulation of
organisms or their components to make useful products.
icrobes to make wine and cheese and the selective breeding of livestock,
are examples of biotechnology.
Now biotechnology based on manipulations of DNA enables scientists to
modify genes and move them between organisms like, bacteria, plants, and
DNA technology is now applied in areas ranging from agriculture to criminal law, but
its most important achievements are in basic research.
disease and insect resistance
salt resistant gene put in rice
rice with beta
carotene for vitamin A (prevents blindness)
a staple in the diets of many
in SE Asia
Cleaning up toxic wastes
take genes from bacteria that can clean toxic wastes and put
in another organism
Production of medications
insulin, growth hormone, vaccines
Concept 20.1 DNA
To study a particular gene, scientists needed to develop methods to isolate only the
defined, portion of a chromosome containing the gene.
s to prepare multiple identical copies
sized pieces of DNA.
Most methods for cloning pieces of DNA share certain general features.
For example, a foreign gene is inserted into a bacterial plasmid (cloning
vector) and this recombinant DNA molecule
is returned to a bacterial cell.
Every time this cell reproduces, the recombinant plasmid is replicated as well
and passed on to its descendents.
Under suitable conditions, the bacterial clone will make the protei n encoded by
the foreign gene.
c cloning technique begins with the insertion of a foreign gene into a
The potential uses of cloned genes fall into two general categories.
First, the goal may be to produce a protein product.
For example, bacteria carrying the gene for human growth hormone can
produce large quantities of the hormone for treating stunted growth.
Alternatively, the goal may be to prepare many copies of the gene itself.
This may enable scientists to determine the
gene’s nucleotide sequence or
provide an organism with a new metabolic capability by transferring a gene
from another organism.
DNA cloni ng is the best method for preparing large quantities of a particular gene or
other DNA sequence.
When the source
of DNA is scanty or impure, the
polymerase chain reaction
) is quicker and more selective.
This technique can quickly amplify any piece of DNA without using cells.
The DNA is incubated in a
test tube with special DNA polym
erase, a supply of
des, and short pieces of
stranded DNA as a primer.
PCR can make billions of copies of a targeted DNA segment in a few hours.
This is faster than cloning via recombinant bacteria.
In PCR, a three
step cycle: heating, cooling, and replication, brings
about a chain
reaction that produces an exponentially growing population of DNA molecules.
The key to easy PCR automation was the discovery of an unusual DNA
polymerase, isolated from bacteria living in hot springs, which can withstand
the heat needed to
separate the DNA strands at the start of each cycle.
Devised in 1985, PCR has had a major impact on biological research and
PCR has amplified DNA from a variety of sources:
fragments of ancient DNA from a 40,000
old frozen wooly mammoth,
DNA from ti ny amount of blood or semen found at the scenes of violent crimes,
DNA from single embryonic cells for rapid prenatal diagnosis of genetic
DNA of viral genes from cells infected with difficult
detect viruses such as
Concept 20.2 DNA Technology Applied to Studying Genes
DNA cloning allows researchers to
Compare genes and alleles between individuals
Locate gene expression in a body
Determine the role of a gene in an organism
Several techniques are used to analyze the D
NA of genes
One indirect method of rapidly analyzing and comparing genomes is
This technique uses a gel as a molecular sieve to separate nucleic acids or proteins
A current is applied that causes charged molecules to move
through the gel
Molecules are sorted into “bands” by their size
Concept 20.3 Cloning
Organismal cloning produces one or more organisms genetically identical to the
“parent” that donated the single cell
In nuclear transplantation, the nucleus of an unfe
rtilized egg cell or zygote is
replaced with the nucleus of a differentiated cell
Experiments with frog embryos have shown that a transplanted nucleus can often
support normal development of the egg
However, the older the donor nucleus, the lower the perce
ntage of normally
In 1997, Scottish researchers announced the birth of Dolly, a lamb cloned from an
adult sheep by nuclear transplantation from a differentiated mammary cell
Dolly’s premature death in 2003, as well as her arthritis,
led to speculation that her
cells were not as healthy as those of a normal sheep, possibly reflecti ng incomplete
reprogramming of the original transplanted nucleus
Since 1997, cloning has been demonstrated in many mammals, including mice,
cats, cows, hor
ses, mules, pigs, and dogs
CC (for Carbon Copy) was the first cat cloned; however, CC differed somewhat from
her female “parent
: repairing damaged or diseased organs
Stem cells: unspecialized cell that can reproduce and can, under
differentiate into specialized cells
Embryonic: can become anything
Adult: can generate some cells; ex. Bone marrow
Totipotent cell: can give rise to all the specialized cell types of the organism
Must be able to obtain a stem
cell and get it to differentiate
Concept 20.4 DNA Tech Applications
Techniques for gene manipulation hold great potential for treating disease by
This alters an afflicted individual’s genes.
A normal allele is inserted into somatic cells of
a tissue affected by a genetic
For gene therapy of somatic cells to be permanent, the cells that receive the
normal allele must be ones that multiply throughout the patient’s life.
Gene therapy raises some difficult ethical and social quest
Some critics suggest that tampering with human genes, even for those with
threatening diseases, is wrong.
They argue that this will lead to the practice of eugenics, a deliberate effort to
control the genetic makeup of human populations.
most difficult ethical question is whether we should treat human embryo cells to
correct the defects of future generations.
In laboratory mice, transferring foreign genes into egg cells is now a routine
Once technical problems relati ng to simila
r genetic engi neering in humans are
solved, we will have to face the question of whether it is advisable, under any
circumstances, to alter the genomes of human embryos.
Should we interfere with evolution in this way?
From a biological perspective, the e
limination of unwanted alleles from the gene
pool could backfire.
Genetic variation is a necessary ingredient for the survival of a species as
environmental conditions change with time.
Genes that are damaging under some conditions could be advantageous
der other conditions, for example the sickle
As with all new technologies, developments in DNA technology have ethical
Who should have the right to examine someone else’s genes?
How should that information be used?
Should a person’s genome be a factor i n suitability for a job or eligibility for life
Some jobs check your credit, why not your genes?
The power of DNA technology and genetic engineering demands that we proceed
with humility, caution, and respe