Question 1
Three major types of RNAs were discussed in some detail: mRNA, rRNA, and tRNA. For
each of the conditions below predict the consequences in terms of the population of
proteins being synthesized in a particular cell. What qualitative and quantitative changes,
if any, are expected in the individual protein involved (if one is involved) and in the
population of proteins produced in that cell?
(a) An acridine dye-induced mutation in mRNA. The condition is heterozygous in the
involved cell.
(b) A deletion (homozygous) that removes approximately half of the rRNA genes.
Separate and clearly label your answers for parts a-b in the box below.
CORRECT ANSWER
(a) Population of proteins: Half of the protein products of that gene will be defective, and
the other half will be normal. Individual protein: The protein should show multiple amino
acid substitutions "downstream" from the point of the mutation. If a nonsense triplet is
introduced, the protein would be shortened in the substituted region.
(b) Population of proteins: There would be an overall reduction in protein synthesis.
Individual protein: All of the proteins would be made in their normal form, but at reduced
levels.
Question 2
1
@THE STUDY VAULT
,Describe what is meant by the term forward genetics.
CORRECT ANSWER
Forward genetics involves the isolation of mutants that show differences in a particular
phenotype of interest. Mutant isolation is usually followed by an analysis of gene pathways
through epistasis and/or complementation analyses. Then the gene is usually mapped and
cloned and studied by a variety of molecular and developmental approaches.
Question 3
Complementation analysis can be used to determine whether two mutations are in the
same gene. Explain how to test for complementation and how one would interpret the
results.
CORRECT ANSWER
A cross is made between the two homozygous strains. If the F1 progeny are wild type,
complementation has occurred and the two mutations must lie in two separate genes.
Question 4
What are the basic regulatory elements in a strand of DNA that allow for genes to be
regulated? Are these different in eukaryotes and prokaryotes? If so, how?
CORRECT ANSWER
Promoters, operators in prokaryotes.
Promoters, proximal promoter elements, enhancers, and silencers in eukaryotes.
Eukaryotic transcription is different in a few ways, most notably in that prokaryotic genes are
transcribed as operons, while eukaryotic genes are not. In addition, the role of the
nucleosome is different in eukaryotic transcription.
2
@THE STUDY VAULT
,Question 5
Explain why mutations in the lacI gene are trans in their effects, but mutations in the lacO
gene are cis in their effects.
CORRECT ANSWER
The lacI gene encodes the lac repressor protein, which can diffuse within the cell and attach
to any operator. It can therefore affect the expression of genes on the same or different
molecules of DNA. The lacO gene encodes the operator. It affects the binding of DNA
polymerase (OR the lacI repressor) to the DNA, and therefore affects only the expression of
genes on the same molecule of DNA.
Question 6
The _________________, which binds to a core promoter, consists of general transcription
factors and RNA polymerase
CORRECT ANSWER
basal transcription apparatus
Question 7
What symbols are used to describe constitutive mutations in the lac operon
CORRECT ANSWER
I-, O^c
Question 8
High-throughput technologies such as DNA and protein expression _________ are often
used to provide a global picture of gene expression
CORRECT ANSWER
microarrays
3
@THE STUDY VAULT
, Question 9
Approximately 5% of the cytosine residues are methylated in the genome of any given
eukaryote. In what way is DNA methylation related to genetic regulation?
CORRECT ANSWER
There is an inverse relationship between the degree of methylation of eukaryotic DNA and
the degree of gene expression
Question 10
Constitutive mutations may occur in various components of the lac operon. Name two
genes of the lac operon in which constitutive mutations could occur.
CORRECT ANSWER
lacI and lacO
Question 11
What are the approximate positions (in bp) of each type of consensus sequence (modular
element) found at the 5' end of eukaryotic genes?
CORRECT ANSWER
TATA is -30 bp relative to transcription start site
GC box -110 bp
CAAT box -70bp
4
@THE STUDY VAULT
Three major types of RNAs were discussed in some detail: mRNA, rRNA, and tRNA. For
each of the conditions below predict the consequences in terms of the population of
proteins being synthesized in a particular cell. What qualitative and quantitative changes,
if any, are expected in the individual protein involved (if one is involved) and in the
population of proteins produced in that cell?
(a) An acridine dye-induced mutation in mRNA. The condition is heterozygous in the
involved cell.
(b) A deletion (homozygous) that removes approximately half of the rRNA genes.
Separate and clearly label your answers for parts a-b in the box below.
CORRECT ANSWER
(a) Population of proteins: Half of the protein products of that gene will be defective, and
the other half will be normal. Individual protein: The protein should show multiple amino
acid substitutions "downstream" from the point of the mutation. If a nonsense triplet is
introduced, the protein would be shortened in the substituted region.
(b) Population of proteins: There would be an overall reduction in protein synthesis.
Individual protein: All of the proteins would be made in their normal form, but at reduced
levels.
Question 2
1
@THE STUDY VAULT
,Describe what is meant by the term forward genetics.
CORRECT ANSWER
Forward genetics involves the isolation of mutants that show differences in a particular
phenotype of interest. Mutant isolation is usually followed by an analysis of gene pathways
through epistasis and/or complementation analyses. Then the gene is usually mapped and
cloned and studied by a variety of molecular and developmental approaches.
Question 3
Complementation analysis can be used to determine whether two mutations are in the
same gene. Explain how to test for complementation and how one would interpret the
results.
CORRECT ANSWER
A cross is made between the two homozygous strains. If the F1 progeny are wild type,
complementation has occurred and the two mutations must lie in two separate genes.
Question 4
What are the basic regulatory elements in a strand of DNA that allow for genes to be
regulated? Are these different in eukaryotes and prokaryotes? If so, how?
CORRECT ANSWER
Promoters, operators in prokaryotes.
Promoters, proximal promoter elements, enhancers, and silencers in eukaryotes.
Eukaryotic transcription is different in a few ways, most notably in that prokaryotic genes are
transcribed as operons, while eukaryotic genes are not. In addition, the role of the
nucleosome is different in eukaryotic transcription.
2
@THE STUDY VAULT
,Question 5
Explain why mutations in the lacI gene are trans in their effects, but mutations in the lacO
gene are cis in their effects.
CORRECT ANSWER
The lacI gene encodes the lac repressor protein, which can diffuse within the cell and attach
to any operator. It can therefore affect the expression of genes on the same or different
molecules of DNA. The lacO gene encodes the operator. It affects the binding of DNA
polymerase (OR the lacI repressor) to the DNA, and therefore affects only the expression of
genes on the same molecule of DNA.
Question 6
The _________________, which binds to a core promoter, consists of general transcription
factors and RNA polymerase
CORRECT ANSWER
basal transcription apparatus
Question 7
What symbols are used to describe constitutive mutations in the lac operon
CORRECT ANSWER
I-, O^c
Question 8
High-throughput technologies such as DNA and protein expression _________ are often
used to provide a global picture of gene expression
CORRECT ANSWER
microarrays
3
@THE STUDY VAULT
, Question 9
Approximately 5% of the cytosine residues are methylated in the genome of any given
eukaryote. In what way is DNA methylation related to genetic regulation?
CORRECT ANSWER
There is an inverse relationship between the degree of methylation of eukaryotic DNA and
the degree of gene expression
Question 10
Constitutive mutations may occur in various components of the lac operon. Name two
genes of the lac operon in which constitutive mutations could occur.
CORRECT ANSWER
lacI and lacO
Question 11
What are the approximate positions (in bp) of each type of consensus sequence (modular
element) found at the 5' end of eukaryotic genes?
CORRECT ANSWER
TATA is -30 bp relative to transcription start site
GC box -110 bp
CAAT box -70bp
4
@THE STUDY VAULT
