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c)
To clone a gene, a vector is first prepared. To genetically
engineer a plasmid or virus, restriction enzymes are
used to cleave plasmid DNA and foreign DNA. The "sticky
ends" produced facilitate the insertion of foreign DNA
into vector DNA. The foreign gene is sealed into the vector DNA by DNA ligase. When the plasmid replicates or
the virus reproduces, the foreign gene is cloned.
The polymerase chain reaction (PCR) uses the
enzyme DNA polymerase to make multiple copies of target DNA. Then the base sequence of this DNA can be
determined, or it can be subjected to DNA fingerprinting.
During DNA fingerprinting, restriction enzymes are
used to fragment DNA. Gel electrophoresis separates the
fragments according to size and charge. Analysis of the
resulting pattern identifies the DNA as belonging to a
particular human or other organism.
Biotechnology products include bacteria, plants,
and animals that have been genetically modified. These
become commercial products of interest to humans, such
as hormones and vaccines. Transgenic bacteria also per-
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form oil spill cleanup and produce chemicals. Transgenic agricultural plants have been engineered to resist
herbicides and pests. Transgenic animals have been
given bovine growth hormone. Cloning of animals is
now possible.
Genomics is the study of the genome. Genomics
should allow a counselor to properly interpret the genetic profile. Genetic profiles can be easily obtained by
the use of a DNA chip that contains all our genes. Genetic
profiles have three benefits: preventive therapy, appropriate drug therapy, and better gene therapy.
Gene therapy is used to correct an individual's genotype and to cure various human ills. Ex vivo gene therapy involves withdrawing cells from the patient; inserting
a functioning gene, usually via a retrovirus; and then returning the treated cells to the patient. Many investigators are trying to develop in vivo gene therapy, in which
viruses, laboratory-grown cells, or synthetic chemicals
can be used to carry healthy genes into the patient.
Study the text section by section as you answer the questions that follow.
• Using recombinant DNA technology, bacteria and viruses can be genetically engineered to clone a gene.
• The polymerase chain reaction (PCR) makes multiple copies of DNA segments. Analysis of the DNA usually
follows.
133
In the following diagram, write the numbers of the appropriate descriptions in the blanks.
1. Cloning occurs.
2. Host cell takes up recombined plasmid.
3. DNA ligase seals human gene and plasmid.
4. Restriction enzyme cleaves DNA.
2. What is meant by the expression that restriction enzymes produce "sticky ends"?
3. Change the following false statements to true statements:
a. Plasmids are used as vectors in genetic engineering experiments involving humans. Rewrite:
b. Recombinant DNA contains two types of bacterial DNA recombined together. Rewrite:
c. Gene cloning occurs when an organism, such as a bacterium, produces many copies of various genes.
Rewrite:
134
In questions 4-6, fill in the blanks.
4. For human gene expression to take place in bacteria, the genes must be accompanied by a.
regions, necessary for the expression of mammalian genes. If genes have been made using reverse
but not the introns.
transcriptase, then the cDNA contains the b.
and what chain
5. Explain the polymerase chain reaction by telling what polymerase refers to: a.
;
reaction means: b.
.
At the beginning of the reaction, very little DNA may be available, but at
the end of the reaction, C.
copies of a segment of DNA are available.
enzymes digest the two samples to be compared. b
6. In DNA fingerprinting, a.
separates the fragments, and their different lengths are compared. If the pattern is identical, the samples are
from C.
'
13:7111119M-1995,1111".....
morrlivirriemmommwrimperprier-,• Bacteria, agricultural plants, and farm animals have been genetically engineered to produce commercially
available products.
• Agricultural plants and farm animals have been genetically engineered to improve their yield.
• It is now possible to clone animals, and cloning is used to produce multiple copies of farm animals that have
been genetically engineered.
7. Complete the following table on transgenic organisms:
Type of Organism
Engineered for What Purpose
8. a. The advantage of using bacteria to make a product is that
b. The advantage of using plants to make a product is that
c. The advantage of using farm animals to make a product is that
9. Put these statements in the proper sequence (1-5) to describe the making of a transgenic female goat that will
produce a medicine needed by humans in its milk.
a.
Zygote develops within a host animal
b.
Remove egg from donor animal
c.
Isolate a human gene
Microinject the human gene into the egg of the donor animal
d.
e.
Transgenic goat is born
10. Put these statements in the proper sequence (1-6) to describe the cloning of the transgenic goat produced in
question 9.
a.
Birth of cloned transgenic goats
Remove nuclei from adult cells of transgenic goat
b.
c.
Collect the milk that contains the medicine of interest
Zygotes develop within host goats
d.
e.
Microinject 2n nuclei into the donor eggs
Remove eggs from donor animal
f.
135
• Genomics is the study of the genome.
• Genetic profiles have many health benefits.
11. Place a check beside those statements that are true.
a.
We now know the sequence of base pairs in the human genome.
b.
We now know the sequence of all the genes on all the human chromosomes.
Humans have hundreds of thousands more genes than do the other animals.
c.
The sequence of the bases in human DNA differs greatly from that of bacteria.
d.
12. The a.
catalogs common sequence differences that occur in human beings. These differences
are called b
Linking these differences may lead to new methods of preventing, diagnosing,
and treating disease.
will soon be
determine how genes work together to control the phenotype. b
13. a.
'
'
available that identify the complete genotype. This knowledge is a step to good health.
• Gene therapy is now being used to replace defective genes with healthy genes and to help cure various human
ills.
14. Change these false statements to true statements.
a. Ex vivo methods of gene therapy require that the therapeutic gene be placed in the body either directly or
by using a viral vector. Rewrite:
h. A common ex vivo method is to microinject normal genes into bone marrow stem cells removed from the
patient. Then the stem cells are returned to the patient. Rewrite:
c. Gene therapy is currently restricted to curing genetic diseases, such as cystic fibrosis, and is not used to treat illnesses,
such as cardiovascular diseases. Rewrite:
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Review key terms by completing this matching exercise, selecting from the following alphabetized list of terms:
clone
DNA ligase
plasmid
polymerase chain
reaction
recombinant DNA
restriction enzyme
transgenic organisms
vector
a.
b.
c.
d.
e.
f.
136
Bacterial enzyme that stops viral reproduction by cleaving
viral DNA; used to cut DNA at specific points during production of recombinant DNA.
Free-living organisms in the environment that have had a
foreign gene inserted into them.
Production of identical copies; in genetic engineering, the
production of many identical copies of a gene.
Self-duplicating ring of accessory DNA in the cytoplasm of
bacteria.
Technique that uses the enzyme DNA polymerase to produce
copies of a particular piece of DNA within a test tube.
DNA that contains genes from more than one source.