MMSC491 EXAM WITH CORRECT
ANSWERS 2025/2026
1. 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?
A) The number of digits a person has.
B) The transcriptome of a single T cell.
C) The sequence of a persons beta globin gene.
D) autistic behavior - ANSWER-The sequence of a persons beta
globin gene.
2. Which, if any, of the following is incorrect? When used in human
genetics,
A) the terms dominant and recessive apply equally to alleles
and phenotypes.
B) dominant describes a phenotype that is manifested in the
heterozygote, that is, the phenotype is attributable to just a
single allele.
C) recessive describes a phenotype that is manifest as a result
of the combined effects of both alleles at a locus.
D) the AB blood group is an example of a co-dominant
phenotype. - ANSWER-the terms dominant and recessive
apply equally to alleles and phenotypes.
3. With respect to autosomal recessive inheritance, which, if any, of
the following statements is incorrect?
A) Affected individuals normally have unaffected parents.
B) 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.
C) Heterozygotes are always asymptomatic carriers.
D) Some affected individuals have alleles with identical
pathogenic mutations but many have two different
mutant alleles and are described as compound
, heterozygotes. - ANSWER-Heterozygotes are always
asymptomatic carriers.
4. 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. - ANSWER-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.
5. With respect to X-linked recessive inheritance, which, if any, of
the following statements is false?
A) Males with just one mutant allele are affected because,
lacking a second X chromosome, they do not have a normal
allele.
B) Women are always asymptomatic.
C) The disorder is not transmitted from fathers to sons.
D) Each child born to a normal man and a carrier woman has a
risk of 1in 4 of being affected. - ANSWER-Women are always
asymptomatic.
6. With respect to X-linked dominant inheritance, which, if any, of
the following statements is false?
A) There are significantly more affected females than males.
, B) Each child born to an affected mother has a risk of 1 in 2 of
being affected.
C) Each daughter born to an affected father has a risk of 1 in 2
of being affected.
D) Each boy born to an affected father has a negligible risk of
being affected. - ANSWER-Each daughter born to an affected
father has a risk of 1 in 2 of being affected.
A) With respect to mitochondrial inheritance, which, if any, of
the following statements is false?
B) Affected individuals can be of either sex.
C) Mitochondrial disorders are transmitted virtually exclusively
through the maternal line.
D) Both the sperm and the egg contribute mitochondrial DNA
to the zygote, however, the paternal mtDNA is destroyed in
the early embryo.
E) Clinical variability is a common feature of mitochondrial DNA
disorders. - ANSWER-All of the statements are true
7. With respect to mosaicism, which, if any, of the following
statements, is false?
A) Any person who has two or more cells that have a different
genetic constitution is a mosaic
B) All women are genetic mosaics
C) Every person is a genetic mosaic.
D) Mosaicism is the inevitable consequence of germline
mutations. - ANSWER-Mosaicism is the inevitable
consequence of germline mutations.
8. Purifying selection results in which of the following?
A) Removes harmful alleles from the population
B) Amplifies genes which can compensate for the loss of
function mutant allele
C) Increases the frequency of a fitness conferring gene in the
population
, D) The process by which DNA is purified to carry out genetic
testing. - ANSWER-Removes harmful alleles from the
population
9. 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. - ANSWER-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.
10. 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. - ANSWER-1. Environmental factors can
lead to different expressions of genes based on the person and
environment they live in.
11. 2. Modifier genes are those that interact with a specific locus,
and this in turn can change how the gene is expressed.
A) 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.
B) 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).
C) 5. Heteroplasmy is the idea that some affected individuals
have both unaffected and mutant copies of alleles, which
ANSWERS 2025/2026
1. 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?
A) The number of digits a person has.
B) The transcriptome of a single T cell.
C) The sequence of a persons beta globin gene.
D) autistic behavior - ANSWER-The sequence of a persons beta
globin gene.
2. Which, if any, of the following is incorrect? When used in human
genetics,
A) the terms dominant and recessive apply equally to alleles
and phenotypes.
B) dominant describes a phenotype that is manifested in the
heterozygote, that is, the phenotype is attributable to just a
single allele.
C) recessive describes a phenotype that is manifest as a result
of the combined effects of both alleles at a locus.
D) the AB blood group is an example of a co-dominant
phenotype. - ANSWER-the terms dominant and recessive
apply equally to alleles and phenotypes.
3. With respect to autosomal recessive inheritance, which, if any, of
the following statements is incorrect?
A) Affected individuals normally have unaffected parents.
B) 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.
C) Heterozygotes are always asymptomatic carriers.
D) Some affected individuals have alleles with identical
pathogenic mutations but many have two different
mutant alleles and are described as compound
, heterozygotes. - ANSWER-Heterozygotes are always
asymptomatic carriers.
4. 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. - ANSWER-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.
5. With respect to X-linked recessive inheritance, which, if any, of
the following statements is false?
A) Males with just one mutant allele are affected because,
lacking a second X chromosome, they do not have a normal
allele.
B) Women are always asymptomatic.
C) The disorder is not transmitted from fathers to sons.
D) Each child born to a normal man and a carrier woman has a
risk of 1in 4 of being affected. - ANSWER-Women are always
asymptomatic.
6. With respect to X-linked dominant inheritance, which, if any, of
the following statements is false?
A) There are significantly more affected females than males.
, B) Each child born to an affected mother has a risk of 1 in 2 of
being affected.
C) Each daughter born to an affected father has a risk of 1 in 2
of being affected.
D) Each boy born to an affected father has a negligible risk of
being affected. - ANSWER-Each daughter born to an affected
father has a risk of 1 in 2 of being affected.
A) With respect to mitochondrial inheritance, which, if any, of
the following statements is false?
B) Affected individuals can be of either sex.
C) Mitochondrial disorders are transmitted virtually exclusively
through the maternal line.
D) Both the sperm and the egg contribute mitochondrial DNA
to the zygote, however, the paternal mtDNA is destroyed in
the early embryo.
E) Clinical variability is a common feature of mitochondrial DNA
disorders. - ANSWER-All of the statements are true
7. With respect to mosaicism, which, if any, of the following
statements, is false?
A) Any person who has two or more cells that have a different
genetic constitution is a mosaic
B) All women are genetic mosaics
C) Every person is a genetic mosaic.
D) Mosaicism is the inevitable consequence of germline
mutations. - ANSWER-Mosaicism is the inevitable
consequence of germline mutations.
8. Purifying selection results in which of the following?
A) Removes harmful alleles from the population
B) Amplifies genes which can compensate for the loss of
function mutant allele
C) Increases the frequency of a fitness conferring gene in the
population
, D) The process by which DNA is purified to carry out genetic
testing. - ANSWER-Removes harmful alleles from the
population
9. 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. - ANSWER-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.
10. 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. - ANSWER-1. Environmental factors can
lead to different expressions of genes based on the person and
environment they live in.
11. 2. Modifier genes are those that interact with a specific locus,
and this in turn can change how the gene is expressed.
A) 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.
B) 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).
C) 5. Heteroplasmy is the idea that some affected individuals
have both unaffected and mutant copies of alleles, which
