MMSC 491 EXAM 2 QUESTIONS WITH VERIFIED
ANSWERS
The term phenotype can be applied to a wide range of manifestations. Which of the
following properties, if any, do not constitute a phenotypic manifestation?
The number of digits a person has.
The transcriptome of a single T cell.
The sequence of a persons beta globin gene.
autistic behavior - Answers - The sequence of a persons beta globin gene.
Which, if any, of the following is incorrect? When used in human genetics,
the terms dominant and recessive apply equally to alleles and phenotypes.
dominant describes a phenotype that is manifested in the heterozygote, that is, the
phenotype is attributable to just a single allele.
recessive describes a phenotype that is manifest as a result of the combined effects of
both alleles at a locus.
the AB blood group is an example of a co-dominant phenotype. - Answers - the terms
dominant and recessive apply equally to alleles and phenotypes.
With respect to autosomal recessive inheritance, which, if any, of the following
statements is incorrect?
Affected individuals normally have unaffected parents.
For unaffected parents who have a previously affected child, there is a 1 in 4 risk of
having an affected child on each occasion that they produce a new child.
Heterozygotes are always asymptomatic carriers.
Some affected individuals have alleles with identical pathogenic mutations but many
have two different mutant alleles and are described as compound heterozygotes. -
Answers - Heterozygotes are always asymptomatic carriers.
With respect to X-chromosome inactivation in females, which, if any, of the following
statements is incorrect?
X-inactivation first occurs in the preimplantation female mammalian embryo.
One of the two X chromosomes in each diploid cell of a normal woman is randomly
selected to undergo X-inactivation and becomes highly condensed.
The process involves epigenetic silencing of each gene on one of the two X
chromosomes, either the maternal X chromosome or the paternal X chromosome.
Once the decision is made to inactivate a paternal X or the maternal X in a cell, all
descendant cells will continue with that pattern of X-inactivation. - Answers - The
process involves epigenetic silencing of each gene on one of the two X chromosomes,
either the maternal X chromosome or the paternal X chromosome.
With respect to X-linked recessive inheritance, which, if any, of the following statements
is false?
,Males with just one mutant allele are affected because, lacking a second X
chromosome, they do not have a normal allele.
Women are always asymptomatic.
The disorder is not transmitted from fathers to sons.
Each child born to a normal man and a carrier woman has a risk of 1in 4 of being
affected. - Answers - Women are always asymptomatic.
With respect to X-linked dominant inheritance, which, if any, of the following statements
is false?
There are significantly more affected females than males.
Each child born to an affected mother has a risk of 1 in 2 of being affected.
Each daughter born to an affected father has a risk of 1 in 2 of being affected.
Each boy born to an affected father has a negligible risk of being affected. - Answers -
Each daughter born to an affected father has a risk of 1 in 2 of being affected.
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. - Answers - 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. - Answers - 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. - Answers - Removes
harmful alleles from the population
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. - Answers - 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. - Answers - 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.
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. - Answers - 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 - Answers - 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
.
ANSWERS
The term phenotype can be applied to a wide range of manifestations. Which of the
following properties, if any, do not constitute a phenotypic manifestation?
The number of digits a person has.
The transcriptome of a single T cell.
The sequence of a persons beta globin gene.
autistic behavior - Answers - The sequence of a persons beta globin gene.
Which, if any, of the following is incorrect? When used in human genetics,
the terms dominant and recessive apply equally to alleles and phenotypes.
dominant describes a phenotype that is manifested in the heterozygote, that is, the
phenotype is attributable to just a single allele.
recessive describes a phenotype that is manifest as a result of the combined effects of
both alleles at a locus.
the AB blood group is an example of a co-dominant phenotype. - Answers - the terms
dominant and recessive apply equally to alleles and phenotypes.
With respect to autosomal recessive inheritance, which, if any, of the following
statements is incorrect?
Affected individuals normally have unaffected parents.
For unaffected parents who have a previously affected child, there is a 1 in 4 risk of
having an affected child on each occasion that they produce a new child.
Heterozygotes are always asymptomatic carriers.
Some affected individuals have alleles with identical pathogenic mutations but many
have two different mutant alleles and are described as compound heterozygotes. -
Answers - Heterozygotes are always asymptomatic carriers.
With respect to X-chromosome inactivation in females, which, if any, of the following
statements is incorrect?
X-inactivation first occurs in the preimplantation female mammalian embryo.
One of the two X chromosomes in each diploid cell of a normal woman is randomly
selected to undergo X-inactivation and becomes highly condensed.
The process involves epigenetic silencing of each gene on one of the two X
chromosomes, either the maternal X chromosome or the paternal X chromosome.
Once the decision is made to inactivate a paternal X or the maternal X in a cell, all
descendant cells will continue with that pattern of X-inactivation. - Answers - The
process involves epigenetic silencing of each gene on one of the two X chromosomes,
either the maternal X chromosome or the paternal X chromosome.
With respect to X-linked recessive inheritance, which, if any, of the following statements
is false?
,Males with just one mutant allele are affected because, lacking a second X
chromosome, they do not have a normal allele.
Women are always asymptomatic.
The disorder is not transmitted from fathers to sons.
Each child born to a normal man and a carrier woman has a risk of 1in 4 of being
affected. - Answers - Women are always asymptomatic.
With respect to X-linked dominant inheritance, which, if any, of the following statements
is false?
There are significantly more affected females than males.
Each child born to an affected mother has a risk of 1 in 2 of being affected.
Each daughter born to an affected father has a risk of 1 in 2 of being affected.
Each boy born to an affected father has a negligible risk of being affected. - Answers -
Each daughter born to an affected father has a risk of 1 in 2 of being affected.
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. - Answers - 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. - Answers - 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. - Answers - Removes
harmful alleles from the population
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. - Answers - 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. - Answers - 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.
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. - Answers - 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 - Answers - 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
.
