Question 1

The 16-kb mitochondrial genome encodes 13 proteins. How can there be more than 13 mitochondrially inherited conditions?
A)Some conditions are due to nuclear genes.
B)Many of the conditions are due to translation errors.
C)There are different kinds and numbers of mutations per gene.
D)Each parent may contribute different mutations.
E)Exon shuffling allows different polypeptides to form.

Accepted Answer

C

Question 2

The human egg has about 2000 mitochondrial genomes, but somatic cells have a range of hundreds to thousands. Which of the following is most likely to account for the difference?
A)Heteroplastic cells can give rise to homoplastic cells.
B)Large mitochondria in oocytes can divide into many smaller mitochondria, and smaller mitochondria can fuse.
C)Specific tissue types replicate organelle DNA far more frequently than they do nuclear DNA.
D)Mutant mitochondria replicate at different frequencies than do wild type.
E)Haploid organelle genomes can replicate to form diploid or polyploidy genomes.

Accepted Answer

The difference in the number of mitochondrial genomes between human eggs and somatic cells is most likely due to the fact that large mitochondria in oocytes can divide into many smaller mitochondria, and smaller mitochondria can fuse, resulting in the accumulation of multiple copies of the mitochondrial genome. This process is not as prevalent in somatic cells, which have a range of hundreds to thousands of mitochondrial genomes depending on the tissue type.

Question 3

Suppose there is (hypothetical)evidence that a gene in mice produces a substance that induces twitchiness in hind leg muscles. A female mouse of a true-breeding twitchy strain is mated with a male of a true-breeding non-twitchy strain. All progeny are twitchy. Which of these procedures would you use to provide evidence for your hypothesis that twitchiness is due to mtDNA?
A)Sequence the mtDNA of the twitchy mother.
B)Breed twitchy male progeny with normal females to show no paternal inheritance.
C)Breed twitchy female with twitchy male F1 mice to verify there is maternal inheritance.
D)Backcross twitchy female offspring with normal fathers.
E)Sequence the mtDNA of the twitchy male offspring.

Accepted Answer

If twitchiness is due to mtDNA, it should be maternally inherited, so breeding twitchy male progeny with normal females should result in non-twitchy offspring, showing no paternal inheritance.

Question 4

Some members of the species D. bifasciata produce mostly female offspring if reared at or below 21°C. The causative agent of this condition (called sex ratio)is a protozoan infection that is lethal to most male larvae. How can you demonstrate that it is both inherited and extrachromosomal?
A)Inject ooplasm of affected females into normal females and then mate these with normal males.
B)Inject cytoplasm from somatic cells of an affected female into normal females and then mate them with normal males.
C)Mate affected females with normal males and assess daughter somatic cells for presence of the protozoan.
D)Perform reciprocal crosses of affected and normal individuals and examine the offspring for infection.
E)Perform reciprocal crosses of affected and normal individuals and look for affected male offspring.

Accepted Answer

Injecting ooplasm (which contains cytoplasmic elements) from affected females into normal females and observing the inheritance pattern in offspring can demonstrate extrachromosomal inheritance, as the protozoan is likely transmitted through the cytoplasm.

Question 5

Sigma virus infection in Drosophila melanogaster causes flies to become paralyzed and then die in high concentrations of CO₂. The virus is passed on extrachromosomally. Two isogenic strains Of Drosophila cultures are maintained: R (resistant to CO₂ or wild type)and S (susceptible to CO₂, infected with sigma). After crosses between male R and female S flies, subsets of offspring of each gender are tested for CO₂ sensitivity. Which of the following results do you expect? A)All the offspring are sensitive. B)All the offspring are female. C)All the offspring are male. D)All the offspring are sensitive, but only males pass it on. E)Only male offspring backcrossed to the female parent are sensitive.

Accepted Answer

The sigma virus is passed on extrachromosomally, typically through the cytoplasm of the egg. Since the female S flies are infected, they will pass the virus to all their offspring, making them all sensitive to CO2.

Question 6

Chlamydomonas, although a green algae, is sensitive to an antibiotic, erythromycin. If mt^- mating-type alga that is sensitive is mated with an mt⁺ cell that is resistant, and if the mt⁺ strain donates chloroplasts, what results do you expect and why? A)All progeny are sensitive because sensitivity is the dominant trait. B)Approximately half the progeny are sensitive because this is the recessive trait. C)All the progeny are sensitive because this is the recessive trait. D)All progeny are resistant because cpDNA is responsible. E)Approximately half the progeny are sensitive because cpDNA is responsible.

Accepted Answer

The mt⁺ strain donates chloroplasts, and since chloroplast DNA (cpDNA) is responsible for the resistance, all progeny will inherit the resistant trait from the mt⁺ parent.

Question 7

Among the discoveries that Correns and Bauer (1908)made in plants was that, sometimes, reciprocal crosses resulted in what phenotype only?

Accepted Answer

The answer of Among the discoveries that Correns and Bauer...

Question 8

When a cell divides, chloroplasts are randomly distributed. What is this called?

Accepted Answer

The answer of When a cell divides, chloroplasts are randomly...

Question 9

Two databases, OMIM and Mitomap, are especially useful in exploring human mitochondrial mutations. If you are interested in learning whether aminoglycoside-induced deafness is inherited maternally, and what gene(s)is/are involved, which of the following would give you the most information?
A)the Mitomap position map with gene names
B)the sequence with specifically altered amino acid coding
C)the OMIM description of symptoms and diagnosis
D)the OMIM description of the TRMU gene at 22q13
E)the Mitomap loci of genes associated with deafness

Accepted Answer

Mitomap is a specialized database for mitochondrial DNA, and the loci of genes associated with deafness would provide specific information on mitochondrial mutations related to aminoglycoside-induced deafness, which is maternally inherited.

Question 10

Myoclonal epilepsy and ragged red fiber disease (MERRF)is a human condition named for the ragged red fibers of skeletal muscle cells and myoclonic epilepsy in affected individuals. People with this disorder have a mutation in a mitochondrial gene for a tRNA, specifically that for lysine. Affected individuals are heteroplastic. Why?
A)Interference with translation slows protein formation and therefore maintenance of mutation-bearing organelles.
B)Having homoplastic organelles would no doubt be lethal due to curtailed translation.
C)Lysine is required in translation of every one of the mitochondrial genes.
D)Mutations of this gene affect individuals before birth.
E)Mutations of this gene are inherited as dominant characteristics.

Accepted Answer

Heteroplasmy refers to the presence of both normal and mutated mitochondrial DNA in the same cell. In MERRF, the mutation affects the mitochondrial gene for a tRNA, specifically that for lysine. Having homoplastic organelles (containing only mutated or only normal mitochondrial DNA) would not be compatible with life due to the importance of mitochondrial function. Therefore, heteroplasmy allows for a distribution of organelles containing both normal and mutated DNA, allowing for some mitochondrial function to still occur despite the mutation.

Question 11

Organisms have been created by nuclear transfer cloning, in which a diploid nucleus from a somatic cell of an adult animal is injected into an enucleated egg cell to create an embryo. Among the many species thus cloned, there has been a prevalence of mitochondrial defects. Which of the following is the most likely explanation?
A)The transferred nucleus may destroy the egg mitochondria.
B)The egg cell may be heteroplastic before injection.
C)The somatic cell's mitochondria may have been transferred as well.
D)The transferred nucleus may have mutations that alter mitochondrial function.
E)The egg nucleus may have had one or more mutations that alter mitochondrial function.

Accepted Answer

The transferred nucleus may have mutations that alter mitochondrial function. Mitochondria have their own genome, which is separate from the nuclear genome, and thus mutations in the nucleus may not necessarily affect mitochondrial function. However, in nuclear transfer cloning, the transferred nucleus may have mutations that can affect mitochondrial function, leading to the prevalence of mitochondrial defects in cloned organisms.

Question 12

Random segregation of organelles during cell division is likely to result in an increased rate of which of the following?
A)incomplete penetrance
B)dominant loss-of-function mutations
C)dominant gain-of-function mutations
D)chromosomal duplication mutations
E)chromosomal deletion mutations

Accepted Answer

Random segregation of organelles during cell division can lead to incomplete penetrance because it may result in unequal distribution of organelles, such as mitochondria, which can affect the expression of traits that depend on organelle function.

Question 13

You are a genetic counselor working with a phenotypically normal young couple who have been referred because the wife has a family history of a mitochondrial disorder that results in considerable dysfunction. What is the most important consideration you can suggest?
A)to refrain from having children that are hers biologically
B)that she be tested to find out what percentage of her mitochondria bear the mutation
C)that both husband and wife have mtDNA testing for the sequence in question
D)that her affected mother's DNA be tested
E)that they consider having only sons

Accepted Answer

Testing the wife to find out what percentage of her mitochondria bear the mutation is important because mitochondrial disorders can be transmitted maternally, meaning that the offspring inherit their mitochondria from their mother. If the wife has a high percentage of mutated mitochondria, the risk of her passing on the disorder to her offspring increases. This information can inform the couple's decision about reproduction options, such as using donor eggs or pursuing adoption. Testing the husband and wife for the sequence in question (choice C) is also important, but knowing the wife's mitochondrial mutation load is a more pressing consideration. Refraining from having children biologically (choice A) or only having sons (choice E) may not be viable options for some couples, and testing the affected mother's DNA (choice D) may not provide useful information since it is already known that she carries the mutation.

Question 14

In 1918, the tsar and tsarina of Russia and their five children were presumably assassinated and buried in an unmarked grave. Later, several women came forward and claimed that they were in fact Anastasia, one of the daughters whose bones had not been found. More recently, forensic scientists have extracted DNA, including mtDNA, from the skeletal remains. Which of the following samples of mtDNA had to be analyzed to discern which, if any, of the claimants was Anastasia?
A)the tsar, tsarina, and the other assassinated children
B)each of the claimants or their living children
C)the tsarina and the claimants
D)the tsar and tsarina only
E)the tsar and tsarina and living relatives of each of them

Accepted Answer

To determine if any of the claimants was Anastasia, mtDNA from the tsarina (Anastasia's mother) and the claimants would be analyzed, as mtDNA is maternally inherited.

Question 15

In a cross between a petite yeast mutant and a wild-type strain, results showed some petite and some wild-type outcomes. Which of these statements must be true of this petite mutation?
A)It is suppressive.
B)It is a nuclear or segregational mutation.
C)It is a neutral mitochondrial mutation.
D)It replicates faster than wild type.
E)It has small deletions of mitochondrial DNA.

Accepted Answer

The fact that the petite mutation is not completely dominant and some wild-type outcomes were observed suggests that it is a nuclear or segregational mutation rather than a neutral mitochondrial mutation. It is not necessarily suppressive or faster replicating, and there is no information provided to suggest that it has small deletions of mitochondrial DNA.

Question 16

A cell or organism in which all copies of the cytoplasmic organelle gene are the same is said to be __________.
A)homozygous
B)heteroplasmic
C)homoplasmic
D)variegated
E)uniparental

Accepted Answer

Homoplasmic cells or organisms have the same genetic information in all copies of the cytoplasmic organelle gene. Heteroplasmic cells or organisms have different genetic information in different copies of the cytoplasmic organelle gene. Homozygous refers to a single gene locus where both alleles are the same. Variegated refers to a pattern of different colors or forms in a plant or organism, and uniparental refers to inheritance from a single parent.

Question 17

The accompanying hypothetical pedigree is for a family where some members have symptoms of Leigh syndrome, which is caused by an mtDNA mutation that reduces ATPase activity.  Which of the following in the youngest generation might transmit the condition in the future?
A)any of the women
B)any of those affected
C)any of the members of this generation
D)only those with an affected mother
E)any of the affected women

Accepted Answer

The answer of The accompanying hypothetical pedigree is for a...

Question 18

A consequence of organelle heredity is that sequence changes in mtDNA vary more than nuclear DNA in response to reduction in population size. Which of the following does this imply about human evolutionary history?
A)Current human populations must have a much higher mutation rate than ancient populations.
B)Mitochondrial variants in people descending from originally small populations show enough diversity to be used to construct an evolutionary tree.
C)The original human population must have grown to be quite large before its members began migrating to other lands and other continents.
D)Nuclear gene sequencing must be used to resolve the question of human ancestral origins.
E)A single human population, living about 200,000 years ago, could not have given rise to all current human populations.

Accepted Answer

The statement suggests that mitochondrial variants (which are inherited solely from the mother) are useful in constructing an evolutionary tree for human populations that descended from smaller ancestral populations, as these variants show more diversity than nuclear DNA in response to population bottlenecks. This supports the idea that human populations have undergone genetic drift and differentiation, which can be traced through differences in mtDNA sequences.

Question 19

In Leber's disease (LHON), degeneration of the optic nerve results in blindness due to a defect in NADH dehydrogenase affecting electron transport. If this is due to a mutation in a mitochondrial gene, which combination of the following effects would you expect to see when doing a pedigree analysis of a family with LHON? i. variable expressivity
Ii. incomplete penetrance
Iii. progressive blindness over time
Iv. maternal inheritance
V. diminished muscle mass
A)i and ii only
B)ii and iii only
C)iii and iv only
D)i, ii, iii, and v only
E)i, ii, iii, and iv only

Accepted Answer

Leber's Hereditary Optic Neuropathy (LHON) is a mitochondrial disorder, so it follows maternal inheritance. It often shows variable expressivity and incomplete penetrance, meaning not all individuals with the mutation will express the disease, and those who do may have varying severity. Progressive blindness is a characteristic symptom.

Question 20

Variation in numbers of mutated chloroplast genomes can give rise to green, white, or variegated leaves. What color leaves do you expect in offspring of pollen from a white-leafed plant and ovules from a green-leafed plant?

Accepted Answer

The answer of Variation in numbers of mutated chloroplast genomes...

Quiz 19: Cytoplasmic Inheritance and the Evolution of Organelle Genomes

The 16-kb mitochondrial genome encodes 13 proteins. How can there be more than 13 mitochondrially inherited conditions?

The human egg has about 2000 mitochondrial genomes, but somatic cells have a range of hundreds to thousands. Which of the following is most likely to account for the difference?

Some members of the species D. bifasciata produce mostly female offspring if reared at or below 21°C. The causative agent of this condition (called sex ratio) is a protozoan infection that is lethal to most male larvae. How can you demonstrate that it is both inherited and extrachromosomal?

Chlamydomonas, although a green algae, is sensitive to an antibiotic, erythromycin. If mt^- mating-type alga that is sensitive is mated with an mt⁺ cell that is resistant, and if the mt⁺ strain donates chloroplasts, what results do you expect and why?

Among the discoveries that Correns and Bauer (1908)made in plants was that, sometimes, reciprocal crosses resulted in what phenotype only?

When a cell divides, chloroplasts are randomly distributed. What is this called?

Two databases, OMIM and Mitomap, are especially useful in exploring human mitochondrial mutations. If you are interested in learning whether aminoglycoside-induced deafness is inherited maternally, and what gene(s) is/are involved, which of the following would give you the most information?

Random segregation of organelles during cell division is likely to result in an increased rate of which of the following?

You are a genetic counselor working with a phenotypically normal young couple who have been referred because the wife has a family history of a mitochondrial disorder that results in considerable dysfunction. What is the most important consideration you can suggest?

In a cross between a petite yeast mutant and a wild-type strain, results showed some petite and some wild-type outcomes. Which of these statements must be true of this petite mutation?

A cell or organism in which all copies of the cytoplasmic organelle gene are the same is said to be __________.

The accompanying hypothetical pedigree is for a family where some members have symptoms of Leigh syndrome, which is caused by an mtDNA mutation that reduces ATPase activity. Which of the following in the youngest generation might transmit the condition in the future?

A consequence of organelle heredity is that sequence changes in mtDNA vary more than nuclear DNA in response to reduction in population size. Which of the following does this imply about human evolutionary history?

Variation in numbers of mutated chloroplast genomes can give rise to green, white, or variegated leaves. What color leaves do you expect in offspring of pollen from a white-leafed plant and ovules from a green-leafed plant?

Quiz 19: Cytoplasmic Inheritance and the Evolution of Organelle Genomes

The 16-kb mitochondrial genome encodes 13 proteins. How can there be more than 13 mitochondrially inherited conditions?

The human egg has about 2000 mitochondrial genomes, but somatic cells have a range of hundreds to thousands. Which of the following is most likely to account for the difference?

Some members of the species D. bifasciata produce mostly female offspring if reared at or below 21°C. The causative agent of this condition (called sex ratio) is a protozoan infection that is lethal to most male larvae. How can you demonstrate that it is both inherited and extrachromosomal?

Chlamydomonas, although a green algae, is sensitive to an antibiotic, erythromycin. If mt- mating-type alga that is sensitive is mated with an mt+ cell that is resistant, and if the mt+ strain donates chloroplasts, what results do you expect and why?

Among the discoveries that Correns and Bauer (1908)made in plants was that, sometimes, reciprocal crosses resulted in what phenotype only?

When a cell divides, chloroplasts are randomly distributed. What is this called?

Two databases, OMIM and Mitomap, are especially useful in exploring human mitochondrial mutations. If you are interested in learning whether aminoglycoside-induced deafness is inherited maternally, and what gene(s) is/are involved, which of the following would give you the most information?

Random segregation of organelles during cell division is likely to result in an increased rate of which of the following?

You are a genetic counselor working with a phenotypically normal young couple who have been referred because the wife has a family history of a mitochondrial disorder that results in considerable dysfunction. What is the most important consideration you can suggest?

In a cross between a petite yeast mutant and a wild-type strain, results showed some petite and some wild-type outcomes. Which of these statements must be true of this petite mutation?

A cell or organism in which all copies of the cytoplasmic organelle gene are the same is said to be __________.

The accompanying hypothetical pedigree is for a family where some members have symptoms of Leigh syndrome, which is caused by an mtDNA mutation that reduces ATPase activity. Which of the following in the youngest generation might transmit the condition in the future?

A consequence of organelle heredity is that sequence changes in mtDNA vary more than nuclear DNA in response to reduction in population size. Which of the following does this imply about human evolutionary history?

Variation in numbers of mutated chloroplast genomes can give rise to green, white, or variegated leaves. What color leaves do you expect in offspring of pollen from a white-leafed plant and ovules from a green-leafed plant?

Chlamydomonas, although a green algae, is sensitive to an antibiotic, erythromycin. If mt^- mating-type alga that is sensitive is mated with an mt⁺ cell that is resistant, and if the mt⁺ strain donates chloroplasts, what results do you expect and why?