320 MHR • Unit 3 Molecular Genetics
21.You are given three different substances that
are known mutagens. Using a variety of
techniques, you analyze the results of exposure
to these substances. Your findings are shown in
the table at right. Using this information, link
each of the three substances with one of the
following molecular properties:
(a)a molecule that can insert itself between a
purine and a pyrimidine in an intact DNA
strand;
(b)a molecule similar in structure to thymine
but capable of forming a hydrogen bond
with guanine;
(c)a molecule that converts cytosine to a form
that can base-pair with adenine.22.You are given two plasmids, one from each of
two bacterial species. One contains gene A and
the other contains gene B. You wish to create a
single plasmid containing both genes.
(a)Draw a diagram to illustrate the steps you
would take to produce this recombinant
plasmid.Substance in
medium Result of exposure
AB
C
increase in the number of mutant colonies that
synthesize mRNA in which the codon AAA is
replaced by AGA
significantly fewer viable colonies
increase in the number of mutant colonies that
produce modified proteins in which arginine is
replaced by a “stop” codon6.Pseudogenes are slightly altered duplicates of
genes that exist within an organism’s genome.
One organism may have hundreds of
pseudogenes that correspond to a single active
gene. What mechanisms could give rise to such
pseudogenes over the course of time?
7.A research team conducts an Ames test on two
different chemicals. The plate of bacterial cells
exposed to chemical A is found to have 53
viable colonies. The plate of cells exposed to
chemical B is found to have 22 viable colonies.
(a)Which of the two chemicals is the stronger
mutagen?
(b)The control plate is found to have 12 viable
colonies. Is this the result you would
expect? Explain.
8.Describe the process of excision repair. In what
ways is this process similar to DNA
replication? In what ways does it differ?
9.Describe the contributions of the following
researchers to the field of genetic engineering:
(a)Frederick Sanger
(b)Stanley Cohen and Herbert Boyer
(c)John Sanford
(d)Kary Mullis
10.What key features make a restriction
endonuclease a useful tool in genetic
engineering?
11.Describe how a bacterial vector can be used to
amplify a sample of DNA. When would you
choose to use this method rather than the
polymerase chain reaction?12.A PCR chamber in your lab develops a slight
malfunction such that it is unable to heat the
reaction mixture at the start of the reaction
cycle. What would be the effect of this on
the amplification process? Explain.
13.Explain how restriction enzymes, DNA
amplification, and gel electrophoresis can
be used to generate a DNA fingerprint.
14.The reaction medium used in the chain
termination reaction normally contains only a
very low concentration of dideoxynucleotides.
What would be the effect of increasing the
concentration of these molecules? Explain.
15.Describe how plasmids containing genes for
antibiotic resistance can be used to screen
bacterial colonies for recombinant DNA.
16.What problem did Mary Dell Chilton address
with her research using Ti plasmids?
17.An electric current is sometimes used as part
of the process to insert new DNA into a
eukaryotic genome. Explain what the current
does and why this is necessary.
18.Explain why the dissimilar processes of cellular
differentiation in plant and animal cells make
it more difficult to clone animals than plants.
19.Three different adult sheep were involved in
the cloning process that led to the birth of the
lamb Dolly. What were their roles? Which one
was Dolly’s clone?
20.What role can viruses play in gene therapy?
Which characteristics of viruses make them
good candidates for this role?INQUIRY