BIO 3070 Exam 3 Questions With Complete Solutions
(a) What are maternal-effect genes?
(b) When are gene products from these genes made, and where
are they located?
Mastering Genetics visit for instructor-assigned tutorials and
problems.
(c) What aspects of development do maternal-effect genes
control?
(d) What is the phenotype of maternal-effect mutations? Correct
Answers (a)
Genes that control early development are often dependent on the
deposition of their products (mRNA, transcription factors,
various structural proteins, etc.) in the egg by the mother. When
observable, these are maternal-effect genes.
(b) They are made in the early oocyte or nurse cells during
oogenesis and deposited in gradients throughout the egg.
(c) Such maternal-effect genes control early developmental
events such as defining anterior-posterior polarity. Such
products are placed in eggs during oogenesis and are activated
immediately after fertilization.
(d) A variety of phenotypes are possible, including embryonic
lethality, and they are often revealed in the offspring of females.
Maternal effects reveal the genotype of the mother: for example,
females homozygous for deleterious recessive mutations of
maternal-effect genes are sterile.
A bacterial operon is responsible for the production of the
biosynthetic enzymes needed to make the hypothetical amino
acid tisophane (tis). The operon is regulated by a separate gene,
R. The deletion of R causes the loss of enzyme synthe- sis. In
,the wild-type condition, when tis is present, no enzymes are
made; in the absence of tis, the enzymes are made. Muta- tions
in the operator gene (O-) result in repression regardless of the
presence of tis. Is the operon under positive or negative control?
Propose a model for
(a) repression of the genes in the presence of tis in wild-type
cells and
(b) the mutations. Correct Answers The regulatory gene product
is exerting positive control.
(a) In wild-type cells, when tis is present, no enzymes are made;
therefore, tis must inactivate the positive regulatory protein.
When tis is absent, the regula- tory protein is free to exert its
positive influence on
transcription.
(b) Mutations in the operator negate the positive action of the
regulator
A number of experiments have demonstrated that areas of the
genome that are transcriptionally inactive are also resistant to
DNase I digestion. However, transcriptionally active areas are
DNase I sensitive. Describe how DNase I resistance or
sensitivity might indicate transcriptional activity. Correct
Answers When DNA is transcriptionally active, it is in a less
condensed state and as such, more susceptible to DNase
digestion.
A particular type of anemia in humans, called b-thalassemia,
results from a severe reduction or absence of the normal y-
globin chain of hemoglobin. However, the y-globin chain,
normally only expressed during fetal development, can
functionally substitute for y-globin. A variety of studies have
,explored the use of the nucleoside 5-azacytidine for the
expression of y-globin in adult patients with b-thalassemia.
(a) How might 5-azacytidine lead to expression of y-globin in
adult patients?
(b) Explain why this drug may also have some adverse side
effects. Correct Answers g globin is expressed during fetal
development, but becomes silenced, which can be accomplished
by methylation of cyti- dine in a CpG island in or near the
promoter. 5-azacytidine is an analog of cytidine that cannot be
methylated. When incorporated into DNA, it stimulates the
expression of
genes.(b) 5-azacytidine is not gene specific, so it is likely to
have
widespread influence on the genome, which could con-
stitute a considerable health hazard.
Amino acids are classified as positively charged, negatively
charged, or electrically neutral
.(a) Which category includes lysine?(b) How does this property
of lysine allow it to interact with DNA?
(c) How does acetylation of lysine affect its interaction with
DNA, and how is this related to the activation of gene
expression? Correct Answers A. Lysine is a positively charged
amino acid.
B. Positively charged lysine side chains can form ionic bonds
with negatively charged phosphate groups in the DNADNA
backbone.
C. Acetylation of the lysine side chain removes its positive
charge preventing the ionic interaction with phosphate and
decreasing the interaction between the histone and the DNA. As
a result, genes are more accessible and are able to be expressed.
, Annotation involves identifying genes and gene-regulatory
sequences in a genome. List and describe characteristics of a
genome that are hallmarks for identifying genes in an unknown
sequence. What characteristics would you look for in a bacterial
genome? A eukaryotic genome? Correct Answers One usually
begins to annotate a sequence by compar- ing it to known
sequences. Similarity to other annotated sequences often
provides insight as to a sequence's func- tion. Hallmarks to
annotation are the identification ofgene regulatory sequences
found upstream of genes (such as promoters), downstream
elements (termination sequences), and triplet nucleotides that are
part of the coding region of the gene. Bacterial genes do not
contain a number of the elements found in eukaryotic genes, so
their annotation is sometimes less complicated. In eukaryotes,
upstream elements would also include enhancers and silencers
and downstream elements would also include a polyadenylation
signal sequence. In addition, 5′ and 3′ splice sites that
distinguish exons from introns are also used in annotation.
Annotation of the human genome sequence reveals a
discrepancy between the number of protein-coding genes and
the number of predicted proteins actually expressed by the
genome. Proteomic analysis indicates that human cells are
capable of synthesizing more than 100,000 different proteins
and perhaps three times this number. What is the discrepancy,
and how can it be reconciled? Correct Answers Increased
protein production from approximately 20,000 genes is probably
related to alternative splicing and various post translational
processing schemes. In addition, a particular DNA segment may
be read in a variety of ways and in two directions
(a) What are maternal-effect genes?
(b) When are gene products from these genes made, and where
are they located?
Mastering Genetics visit for instructor-assigned tutorials and
problems.
(c) What aspects of development do maternal-effect genes
control?
(d) What is the phenotype of maternal-effect mutations? Correct
Answers (a)
Genes that control early development are often dependent on the
deposition of their products (mRNA, transcription factors,
various structural proteins, etc.) in the egg by the mother. When
observable, these are maternal-effect genes.
(b) They are made in the early oocyte or nurse cells during
oogenesis and deposited in gradients throughout the egg.
(c) Such maternal-effect genes control early developmental
events such as defining anterior-posterior polarity. Such
products are placed in eggs during oogenesis and are activated
immediately after fertilization.
(d) A variety of phenotypes are possible, including embryonic
lethality, and they are often revealed in the offspring of females.
Maternal effects reveal the genotype of the mother: for example,
females homozygous for deleterious recessive mutations of
maternal-effect genes are sterile.
A bacterial operon is responsible for the production of the
biosynthetic enzymes needed to make the hypothetical amino
acid tisophane (tis). The operon is regulated by a separate gene,
R. The deletion of R causes the loss of enzyme synthe- sis. In
,the wild-type condition, when tis is present, no enzymes are
made; in the absence of tis, the enzymes are made. Muta- tions
in the operator gene (O-) result in repression regardless of the
presence of tis. Is the operon under positive or negative control?
Propose a model for
(a) repression of the genes in the presence of tis in wild-type
cells and
(b) the mutations. Correct Answers The regulatory gene product
is exerting positive control.
(a) In wild-type cells, when tis is present, no enzymes are made;
therefore, tis must inactivate the positive regulatory protein.
When tis is absent, the regula- tory protein is free to exert its
positive influence on
transcription.
(b) Mutations in the operator negate the positive action of the
regulator
A number of experiments have demonstrated that areas of the
genome that are transcriptionally inactive are also resistant to
DNase I digestion. However, transcriptionally active areas are
DNase I sensitive. Describe how DNase I resistance or
sensitivity might indicate transcriptional activity. Correct
Answers When DNA is transcriptionally active, it is in a less
condensed state and as such, more susceptible to DNase
digestion.
A particular type of anemia in humans, called b-thalassemia,
results from a severe reduction or absence of the normal y-
globin chain of hemoglobin. However, the y-globin chain,
normally only expressed during fetal development, can
functionally substitute for y-globin. A variety of studies have
,explored the use of the nucleoside 5-azacytidine for the
expression of y-globin in adult patients with b-thalassemia.
(a) How might 5-azacytidine lead to expression of y-globin in
adult patients?
(b) Explain why this drug may also have some adverse side
effects. Correct Answers g globin is expressed during fetal
development, but becomes silenced, which can be accomplished
by methylation of cyti- dine in a CpG island in or near the
promoter. 5-azacytidine is an analog of cytidine that cannot be
methylated. When incorporated into DNA, it stimulates the
expression of
genes.(b) 5-azacytidine is not gene specific, so it is likely to
have
widespread influence on the genome, which could con-
stitute a considerable health hazard.
Amino acids are classified as positively charged, negatively
charged, or electrically neutral
.(a) Which category includes lysine?(b) How does this property
of lysine allow it to interact with DNA?
(c) How does acetylation of lysine affect its interaction with
DNA, and how is this related to the activation of gene
expression? Correct Answers A. Lysine is a positively charged
amino acid.
B. Positively charged lysine side chains can form ionic bonds
with negatively charged phosphate groups in the DNADNA
backbone.
C. Acetylation of the lysine side chain removes its positive
charge preventing the ionic interaction with phosphate and
decreasing the interaction between the histone and the DNA. As
a result, genes are more accessible and are able to be expressed.
, Annotation involves identifying genes and gene-regulatory
sequences in a genome. List and describe characteristics of a
genome that are hallmarks for identifying genes in an unknown
sequence. What characteristics would you look for in a bacterial
genome? A eukaryotic genome? Correct Answers One usually
begins to annotate a sequence by compar- ing it to known
sequences. Similarity to other annotated sequences often
provides insight as to a sequence's func- tion. Hallmarks to
annotation are the identification ofgene regulatory sequences
found upstream of genes (such as promoters), downstream
elements (termination sequences), and triplet nucleotides that are
part of the coding region of the gene. Bacterial genes do not
contain a number of the elements found in eukaryotic genes, so
their annotation is sometimes less complicated. In eukaryotes,
upstream elements would also include enhancers and silencers
and downstream elements would also include a polyadenylation
signal sequence. In addition, 5′ and 3′ splice sites that
distinguish exons from introns are also used in annotation.
Annotation of the human genome sequence reveals a
discrepancy between the number of protein-coding genes and
the number of predicted proteins actually expressed by the
genome. Proteomic analysis indicates that human cells are
capable of synthesizing more than 100,000 different proteins
and perhaps three times this number. What is the discrepancy,
and how can it be reconciled? Correct Answers Increased
protein production from approximately 20,000 genes is probably
related to alternative splicing and various post translational
processing schemes. In addition, a particular DNA segment may
be read in a variety of ways and in two directions
