MMSC491 Exam 2- Questions and Answers
With respect to mitochondrial inheritance, which, if any, of the following statements is false?
Affected individuals can be of either sex.
Mitochondrial disorders are transmitted virtually exclusively through the maternal line.
Both the sperm and the egg contribute mitochondrial DNA to the zygote, however, the
paternal mtDNA is destroyed in the early embryo.
Clinical variability is a common feature of mitochondrial DNA disorders. Correct Ans-All of
the statements are true
With respect to mosaicism, which, if any, of the following statements, is false?
Any person who has two or more cells that have a different genetic constitution is a mosaic
All women are genetic mosaics
Every person is a genetic mosaic.
Mosaicism is the inevitable consequence of germline mutations. Correct Ans-Mosaicism is
the inevitable consequence of germline mutations.
Purifying selection results in which of the following?
Removes harmful alleles from the population
Amplifies genes which can compensate for the loss of function mutant allele
Increases the frequency of a fitness conferring gene in the population
The process by which DNA is purified to carry out genetic testing. Correct Ans-Removes
harmful alleles from the population
, MMSC491 Exam 2- Questions and Answers
List three examples of a single gene disorder where there is extremely limited mutational
heterogeneity and one example where different mutations in one gene result in a wide range
of different diseases. Correct Ans-Three examples of a gene disorder where there is limited
mutational heterogeneity are Huntington's disease (late onset, single gene mutation),
achondroplasia (single nucleotide mutation in a single gene), and cystic fibrosis (recessive, but
single CFTR gene mutation). One example of a gene where different mutations in one gene
result in a wide range of different diseases is the lamin A/C gene in the textbook, which shows
that ten different diseases can arise from different mutations in just one (LMNA) gene.
For some single gene disorders, some members of a family who have the same genetic
variants at the disease locus as strongly affected family members either show a much milder
phenotype or no disease symptoms. List five explanations for why there can be a lack of
penetrance or variable expressivity of a single gene disorder. Correct Ans-1. Environmental
factors can lead to different expressions of genes based on the person and environment they
live in.
2. Modifier genes are those that interact with a specific locus, and this in turn can change how
the gene is expressed.
3. Imprinting is an epigenetic mechanism in which one inherited gene is expressed in the
offspring and the other is not, so if the mutant allele is not expressed we would see a lack of
penetrance.
4. Anticipation happens in disorders with relatively unstable mutations, so as DNA undergoes
replication the phenotype of the disease's expression might change with each generation (can
get better or worse).
5. Heteroplasmy is the idea that some affected individuals have both unaffected and mutant
copies of alleles, which can change the severity to which the gene disorder is expressed.
, MMSC491 Exam 2- Questions and Answers
With respect to how miRNAs work, which, if any, of the following statements, is false?
An miRNA is initially composed of two RNA strands, a passenger strand that will be destroyed
and a complementary RNA, the guide strand, that is required for it to work.
an active miRNA regulates target protein-coding genes by binding to complementary
sequences in the mRNA
A single miRNA normally binds to transcripts from just one target gene
A single type of mRNA can be regulated by multiple different miRNAs. Correct Ans-A single
miRNA normally binds to transcripts from just one target gene
Which, if any, of the following is not regularly an epigenetic phenomenon that depends on
DNA methylation or chromatin modification?
X-chromosome inactivation.
A position effect in which a gene is silenced by an inversion where both breakpoints occur
within a euchromatic environment.
Establishment of heterochromatin at a centromere.
Imprinting Correct Ans-A position effect in which a gene is silenced by an inversion where
both breakpoints occur within a euchromatic environment.
With respect to histone modifications, which, if any, of the following statements, is true?
histone acetylation always means adding an acetyl group to the side chain of a lysine residue.
in histone acetylation each lysine of the histone is acetylated.
in histone phosphorylation a phosphate group is transferred to the side chain of a serine .
, MMSC491 Exam 2- Questions and Answers
in histone methylation it is the DNA that coils around a nucleosome that is methylated, not
the histone itself. Correct Ans-histone acetylation always means adding an acetyl group to
the side chain of a lysine residue.
With respect to noncoding RNA (ncRNA) , which, if any, of the following statements, is false?
Many long noncoding RNAs work in epigenetic regulation of gene expression.
Most regulatory long ncRNAs work as trans-acting regulators.
HOTAIR RNA is produced by a gene in the HOXC homeobox gene cluster at 12q13 but can
regulate multiple genes within the HOXD gene cluster on chromosome 2.
HOTAIR RNA works as a scaffold that binds specific protein regulators at its two ends.
Correct Ans-Most regulatory long ncRNAs work as trans-acting regulators.
With respect to epimutations, which, if any, of the following statements, is false, from a
practical viewpoint?
The term epimutation means an unexpected change in chromatin conformation, causing a g
ene to be expressed in an abnormal way that is not related to its base sequence.
A primary epimutation is a change in chromatin confirmation that is not related directly to
any change in the base sequence.
A secondary epimutation arises from a standard mutation that results in a profound change of
expression in a gene that regulates chromatin conformation.
A Òchromatin diseaseÓ is a disorder that is consistently caused by a primary epimutation.
Correct Ans-A Òchromatin diseaseÓ is a disorder that is consistently caused by a primary
epimutation.
With respect to mitochondrial inheritance, which, if any, of the following statements is false?
Affected individuals can be of either sex.
Mitochondrial disorders are transmitted virtually exclusively through the maternal line.
Both the sperm and the egg contribute mitochondrial DNA to the zygote, however, the
paternal mtDNA is destroyed in the early embryo.
Clinical variability is a common feature of mitochondrial DNA disorders. Correct Ans-All of
the statements are true
With respect to mosaicism, which, if any, of the following statements, is false?
Any person who has two or more cells that have a different genetic constitution is a mosaic
All women are genetic mosaics
Every person is a genetic mosaic.
Mosaicism is the inevitable consequence of germline mutations. Correct Ans-Mosaicism is
the inevitable consequence of germline mutations.
Purifying selection results in which of the following?
Removes harmful alleles from the population
Amplifies genes which can compensate for the loss of function mutant allele
Increases the frequency of a fitness conferring gene in the population
The process by which DNA is purified to carry out genetic testing. Correct Ans-Removes
harmful alleles from the population
, MMSC491 Exam 2- Questions and Answers
List three examples of a single gene disorder where there is extremely limited mutational
heterogeneity and one example where different mutations in one gene result in a wide range
of different diseases. Correct Ans-Three examples of a gene disorder where there is limited
mutational heterogeneity are Huntington's disease (late onset, single gene mutation),
achondroplasia (single nucleotide mutation in a single gene), and cystic fibrosis (recessive, but
single CFTR gene mutation). One example of a gene where different mutations in one gene
result in a wide range of different diseases is the lamin A/C gene in the textbook, which shows
that ten different diseases can arise from different mutations in just one (LMNA) gene.
For some single gene disorders, some members of a family who have the same genetic
variants at the disease locus as strongly affected family members either show a much milder
phenotype or no disease symptoms. List five explanations for why there can be a lack of
penetrance or variable expressivity of a single gene disorder. Correct Ans-1. Environmental
factors can lead to different expressions of genes based on the person and environment they
live in.
2. Modifier genes are those that interact with a specific locus, and this in turn can change how
the gene is expressed.
3. Imprinting is an epigenetic mechanism in which one inherited gene is expressed in the
offspring and the other is not, so if the mutant allele is not expressed we would see a lack of
penetrance.
4. Anticipation happens in disorders with relatively unstable mutations, so as DNA undergoes
replication the phenotype of the disease's expression might change with each generation (can
get better or worse).
5. Heteroplasmy is the idea that some affected individuals have both unaffected and mutant
copies of alleles, which can change the severity to which the gene disorder is expressed.
, MMSC491 Exam 2- Questions and Answers
With respect to how miRNAs work, which, if any, of the following statements, is false?
An miRNA is initially composed of two RNA strands, a passenger strand that will be destroyed
and a complementary RNA, the guide strand, that is required for it to work.
an active miRNA regulates target protein-coding genes by binding to complementary
sequences in the mRNA
A single miRNA normally binds to transcripts from just one target gene
A single type of mRNA can be regulated by multiple different miRNAs. Correct Ans-A single
miRNA normally binds to transcripts from just one target gene
Which, if any, of the following is not regularly an epigenetic phenomenon that depends on
DNA methylation or chromatin modification?
X-chromosome inactivation.
A position effect in which a gene is silenced by an inversion where both breakpoints occur
within a euchromatic environment.
Establishment of heterochromatin at a centromere.
Imprinting Correct Ans-A position effect in which a gene is silenced by an inversion where
both breakpoints occur within a euchromatic environment.
With respect to histone modifications, which, if any, of the following statements, is true?
histone acetylation always means adding an acetyl group to the side chain of a lysine residue.
in histone acetylation each lysine of the histone is acetylated.
in histone phosphorylation a phosphate group is transferred to the side chain of a serine .
, MMSC491 Exam 2- Questions and Answers
in histone methylation it is the DNA that coils around a nucleosome that is methylated, not
the histone itself. Correct Ans-histone acetylation always means adding an acetyl group to
the side chain of a lysine residue.
With respect to noncoding RNA (ncRNA) , which, if any, of the following statements, is false?
Many long noncoding RNAs work in epigenetic regulation of gene expression.
Most regulatory long ncRNAs work as trans-acting regulators.
HOTAIR RNA is produced by a gene in the HOXC homeobox gene cluster at 12q13 but can
regulate multiple genes within the HOXD gene cluster on chromosome 2.
HOTAIR RNA works as a scaffold that binds specific protein regulators at its two ends.
Correct Ans-Most regulatory long ncRNAs work as trans-acting regulators.
With respect to epimutations, which, if any, of the following statements, is false, from a
practical viewpoint?
The term epimutation means an unexpected change in chromatin conformation, causing a g
ene to be expressed in an abnormal way that is not related to its base sequence.
A primary epimutation is a change in chromatin confirmation that is not related directly to
any change in the base sequence.
A secondary epimutation arises from a standard mutation that results in a profound change of
expression in a gene that regulates chromatin conformation.
A Òchromatin diseaseÓ is a disorder that is consistently caused by a primary epimutation.
Correct Ans-A Òchromatin diseaseÓ is a disorder that is consistently caused by a primary
epimutation.
