MMSC491 Exam 2 (Answered) 187 Questions
and Correct Answers. With 100% Verified
Solution. 2025/2026.
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
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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
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 .
in histone methylation it is the DNA that coils around a nucleosome that is methylated, not the
histone itself.
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
and Correct Answers. With 100% Verified
Solution. 2025/2026.
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
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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
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 .
in histone methylation it is the DNA that coils around a nucleosome that is methylated, not the
histone itself.
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
