Answers to Mastering Concepts Questions
11.1
1. What is DNA technology?
DNA technology is the manipulation of genes for a practical purpose.
2. In what fields is DNA technology useful?
DNA technology is useful in studies of evolutionary biology, agriculture, criminal justice,
medicine, and many other fields.
11.2
1. What are some uses for transgenic organisms?
Transgenic organisms can be used for the production of drugs like insulin; degradation of
petroleum and other toxic wastes; the production of herbicide-resistant crop plants; and
the production of human proteins in livestock milk.
2. What are the steps in creating a transgenic organism?
To create a transgenic bacterium, the target DNA must first be identified. A plasmid
must be obtained and restriction enzymes used to open the plasmid. The target DNA is
then spliced into the plasmid. The recombinant plasmid is inserted into a bacterium,
which is then grown in pure culture. The bacterium produces the product encoded by the
gene that was inserted. Methods vary for producing transgenic plants and animals.
3. How do researchers determine a sequence of DNA?
The DNA sample is divided among four test tubes, each containing the unknown
sequence, primers, normal nucleotides (A, C, T, and G), replication enzymes, and a small
amount of one type of terminator nucleotide. Replication results in different-sized
fragments of complimentary copies of the unknown DNA. The fragments are sorted by
size, using electrophoresis; the original sequence is deduced by reading the bands on the
gel. A computer program can also determine gene sequence when fluorescent labels are
used.
4. What is the function of the 98.5% of the human genome that does not encode protein?
Some of it encodes tRNA and rRNA, and some contains regions that regulate gene
expression. Some of it encodes pseudogenes. Much of it, however, has no known
function.
5. How does PCR work and why is it useful?
PCR creates many copies of a tiny sample of DNA. Afterwards, sufficient DNA is
available for sequencing and other forms of analysis. PCR is useful in forensics, disease
diagnosis, and many other fields.
6. How are short tandem repeats used in DNA profiling?
Short tandem repeats are a series of just a few repeating nucleotides that occur in
noncoding portions of DNA. Each individual varies in the number of repeats they
possess on each chromosome, so by combining analysis of several STR sites between
individuals, a DNA profile can be produced.
7. Why does mitochondrial DNA provide different information from nuclear DNA?
Mitochondrial DNA is much shorter than nuclear DNA and exists in many copies (since
each cell contains many mitochondria). It is inherited only from the female parent, so it
cannot be used to distinguish between siblings, but it is useful for tracking inheritance
over two or more generations.
11.3
1. Describe the differences between embryonic, adult, and induced pluripotent stem cells.
Embryonic stem cells are totipotent and give rise to any cell in the body. Adult stem cells
are pluripotent, with the ability to become many (but not all) cell types. Induced
pluripotent stem cells are adult cells that have been manipulated in such a way that they
behave like embryonic stem cells.
2. What are the potential medical benefits of stem cells?
Stem cells help researchers understand how animals develop and grow; they may be
useful in treating diseases that involve tissue loss or damage; and they are useful in
observing the development of a disease from its start. Finally, stem cells may also be
useful in testing for side effects of pharmaceutical drugs.
3. Summarize the steps scientists use to clone an adult mammal.
Cells from the animal to be cloned are grown in culture, and then the nucleus of one of
those cells is removed. That nucleus is then fused with a denucleated cell from an egg
donor. The fused cell is allowed to divide into an embryo and is then implanted into the
surrogate, where it is allowed to develop to birth.
4. Why is the cloning technique called somatic cell nuclear transfer?
The nucleus of a somatic cell is transferred into an egg that has had its own nucleus
removed.
11.4
1. Explain how and why a researcher might use a DNA probe.
DNA probes are used to find a particular DNA sequence. The complimentary strand of
the allele of interest is created and marked with a radioactive isotope or fluorescent tag.
The marked strand will bond with the allele sequence, if it is present, and the tag will
reveal its location.
2. Compare and contrast preimplantation genetic diagnosis and genetic testing.
Preimplantation genetic diagnosis uses a DNA probe to determine whether a cell
removed from an embryo has a particular allele of interest. If the cell contains the allele,
the embryo is not implanted into the uterus; otherwise, the embryo is implanted. Genetic
testing also uses a DNA probe to detect a specific allele, but the test is conducted on cells
taken from a child or adult. Genetic testing allows for a definitive diagnosis, which helps
patients and physicians develop a treatment plan.
3. What is gene therapy?
In gene therapy, a healthy gene can be inserted into cells to compensate for the missing
function of a faulty gene.
4. What are some examples of ethical questions raised by the medical use of DNA
technology?
The methods are expensive and would be cost prohibitive for lower-income individuals.
It could lead to an increase in pregnancy terminations if it is known that the fetus will
have a particular disorder. There are issues with health insurance coverage if it is known
that an individual has a gene for a particular deadly disorder.
11.5
1. What information can researchers gain by comparing the human and chimpanzee
genome sequences?
It can provide scientists with the information about what genes make us human.
Differences in gene expression can also be examined, since so much of the DNA is the
same between humans and chimps yet our appearances are so different. Finally, much
can be learned about diseases that affect humans but not chimps.
2. How do the genome sequences of orangutans and gorillas help scientists further
resolve the evolutionary history of humans?
Orangutans and gorillas are also related to chimps and humans. Studying the gene
variants in the genomes of these other primates can reveal which variants are common to
all primates and which occurred uniquely in the lineages of humans or chimps.
Write It Out
1. What techniques might researchers use to create transgenic bacteria that produce
human growth hormone (a drug used to treat extremely short stature)?
They would begin by identifying the gene that encodes human growth hormone. They
would then use restriction enzymes to cut the gene out of human DNA; they would use
the same restriction enzyme to cut a plasmid. After splicing the gene into the plasmid,
they would induce bacterial cells to take up the plasmid. The bacterial cells would then
produce the protein.
2. Transgenic crops often require fewer herbicides and insecticides than conventional
crops. In that respect, they could be considered environmentally friendly. Use the Internet
to research the question of why some environmental groups oppose transgenic
technology.
Environmental groups may oppose transgenic technology because they believe that
interfering with another species is unethical; that the repercussions on the natural
environment are unknown; that transgenic organisms may escape into the natural
ecosystem; and that transgenic crops are too expensive for ordinary farmers to afford.
(Other arguments are possible as well.)
3. Explain how the ingredients in a PCR reaction tube replicate DNA.
In a PCR reaction tube, heat separates the two strands of target DNA. The temperature is
lowered, then short laboratory-made primers attach to the separated target strands by
complementary base pairing. DNA polymerase adds nucleotides to the primers and
builds sequences complementary to the target sequence. The newly synthesized strands
then act as templates in the next round of replication, which can be initiated immediately
by raising the temperature to separate the strands once more.
4. Compare and contrast the use of the DNA polymerase enzyme in DNA sequencing and
PCR.
Both enzymes produce complementary copies of a DNA sequence of interest. In DNA
sequencing, the enzyme’s progress is intentionally interrupted with terminator
nucleotides. In PCR, the DNA polymerase is heat-tolerant so that it does not become
denatured when the temperature in the reaction tube is periodically raised.
5. Why does DNA profiling require an understanding of probability?
Allele frequencies vary within the population for each STR locus. An understanding of
probability is necessary to calculate the likelihood that two people share the exact same
DNA profile, simply by chance.
6. Make a chart that lists the advantages and disadvantages of embryonic stem cells, adult
stem cells, and induced pluripotent stem cells.
Embryonic stem cells must be harvested from embryos, but they have the most potential
to develop into every cell type in the body. Adult stem cells do not require embryos, but
they are less versatile than embryonic stem cells. Induced pluripotent stem cells also
come from adults, and they may one day be as versatile as embryonic stem cells, but we
cannot yet manipulate them to develop into any cell type.
7. Unneeded genes in an adult animal cell are permanently inactivated, making it
impossible for most specialized cells to turn into any other cell type. How does this
arrangement save energy inside a cell? Why does the ability to clone an adult mammal
depend on techniques for reactivating these “dormant” genes?
Permanently inactivating unneeded genes reduces the chance that they will be expressed;
protein production costs energy, so preventing unneeded gene expression saves energy.
These genes must be reactivated in cloning because many are required for the proper
development of an embryo.
8. Search the Internet for examples of mammals that have been cloned (other than sheep).
What ethical issues should people consider in deciding whether to clone plants,
nonhuman animals, and humans?
[Answers will vary.]
9. This chapter’s Apply It Now box describes some potential applications of gene doping.
What are some examples of ethical issues that gene doping presents? What might the
prospect of gene doping mean for the future of sports?
Gene doping may give athletes with money and/or a high risk tolerance an unfair
advantage over those who choose not to use the technique. Because gene doping is hard
to detect, it may lead to an “arms race” in which elite athletes must “enhance” themselves
in more and more ways, simply to remain competitive.
10. Describe gene therapy and explain the ethical issues that gene therapy presents.
In gene therapy, a healthy gene is placed into a cell to make up for the function of a faulty
gene. Ethical issues include high cost and the prospect of fixing genes in germ cells,
which would mean that gene “repairs” could be passed on to the next generation. The
potential consequences of germline gene therapy are unknown.
11. If a cell’s genome is analogous to a cookbook and a gene is analogous to a recipe,
what is an analogy for preimplantation genetic diagnosis? For gene testing? For gene
therapy?
Preimplantation genetic diagnosis would be like peeking into a cookbook before it is
published to see if it contains a particular recipe. Gene testing would be the same, only
the cookbook would already be published. Gene therapy would be like adding a new
recipe that corrects errors in an existing recipe.
Answers to Pull It Together Questions
1. What is recombinant DNA?
Recombinant DNA contains DNA from two or more different species.
2. Add the terms restriction enzyme, plasmid, virus, DNA polymerase, and short tandem
repeat to this concept map.
“Restriction enzyme” leads with the word “cuts” to “DNA.” “Plasmid” connects with the
phrase “may carry DNA into” to “Transgenic organism.” “Virus” connects with the
phrase “may carry DNA in” to “Gene therapy.” “DNA polymerase” connects with the
phrase “copies DNA in” to “PCR” and to “DNA sequencing.” “Short tandem repeat”
connects with the phrase “is used in” to “DNA profiling.”
3. How is a patient who receives gene therapy similar to and different from a transgenic
organism?
A patient who receives gene therapy receives human DNA; a transgenic organism
receives DNA from another species.