Deck 19: Cytoplasmic Inheritance and the Evolution of Organelle Genomes

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.

Answer 1

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.

Answer 2

B

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.

Answer 3

B

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.

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.

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.

Question 7

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

Question 8

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

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

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.

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.

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

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

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

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.

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

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

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.

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

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?

Question 21

Three of the four modes of inheritance of organelle genes are
• maternal inheritance as in mammals,
• paternal inheritance as in gymnosperms, and
• selective degradation of one source during mating.
What is the fourth?

Question 22

Do the protein-coding parts of organelle genes more closely resemble those of Bacteria (Eubacteria)or Archaea?

Question 23

Mating in Chlamydomonas occurs between haploid mt⁺ and mt^- individuals. The mt^- chloroplast genome is selectively degraded 95% of the time. In one such mating, the mt⁺ genome is str^R and
mt^- is str^S. Will offspring live or die if they are exposed to streptomycin?

Question 24

In mammals, the number of mitochondria per cell is highly variable. Which of the following would have the largest number: skin cells, red blood cells, or skeletal muscle cells?

Question 25

In one or two words, give two characteristics of mitochondrial genomes.

Question 26

Which factor in organelle replication immediately precedes "organelle division"?

Question 27

DNA transfer has occurred many times between organelle and nuclear genomes. Two pairs of sequences are analyzed. Pair A has more similarities than pair B. Which of these is the most ancient transfer?

Question 28

If a cell includes a mixture of variable numbers of wild-type and mutant organelles, this condition is known as ________.

Question 29

What name is given to the alteration of an RNA sequence after transcription?

Question 30

What is the name of the area of the organelle in which organelle DNA is packaged?

Question 31

If a chloroplast coding sequence has been transferred to the nuclear genome, but the protein product is needed in the chloroplast, what must be added to the original polypeptide sequence?

Question 32

The organelles involved in organelle heredity are ________ and ________.

Question 33

What are the closest "relatives" of chloroplasts still found as free-living organisms today?

Question 34

Sequencing of genomes of eukaryotes, both mitochondrial and nuclear, have revealed evidence of sequence transfer from one to the other. Are such transfers ancient, recent, or both?

Question 35

In any mammal, the phenotype for a mitochondrial trait is based on what maternal characteristic?

Question 36

Mitochondrial genome transcription, translation, and replication occur where?

Question 37

The protein-coding genes of chloroplasts are involved in what part of photosynthesis?

Question 38

Is the rate of mutation in mitochondrial DNA of mammals greater or less than that of the species' nuclear DNA?

Question 39

Any form of inheritance that does not follow Mendelian patterns and that involves most of the cytoplasm being contributed to the embryo by one of the parents is called ________.

Question 40

Allan Wilson showed that the mtDNA of Africans is more diverse than that of other human populations. Does this finding provide evidence for the multiregional (MRE)model or the recent African origin (RAO)model?

Question 41

What makes it possible for human mitochondria, which have only 22 sequences that code for tRNA, to translate mitochondrial polypeptides that require 32 tRNAs?

Question 42

How can you establish that, in a newly described species of plant, a particular phenotype is due to a chloroplast rather than a nuclear gene?

Question 43

The chloroplast is derived from a precursor organelle called a _____.

Question 44

In a plant, analysis of Rubisco reveals that, in some proteins, rbcL is deficient while rbcS is normal. In other Rubisco proteins, both rbcL and rbcS are normal. What does this indicate about the two genes encoding these subunits?

Question 45

Transcriptional regulation of mitochondrial genes closely resembles regulation of _______ operons.

Question 46

In the 1950s, mitochondrial genomes were discovered by differential staining for ________.

Question 47

Among current bacteria, those with the most in common with mitochondria are the Rickettsia (that cause typhus). What does this mean about Rickettsia's place in the evolution of endosymbiosis?

Question 48

How can you explain the fact that protein synthesis proceeds normally in mammals in which not all mitochondrial tRNAs are encoded in mitochondrial DNA?

Question 49

Mitochondrial mutations in mammals are passed to the offspring by the ________ parent.

Question 50

What is the argument that, although human mitochondria all descend from a single ancestral population, this may not be true for nuclear genomes?

Question 51

If the mother and grandmother of a given family both exhibit a half dozen phenotypic effects of a mitochondrial disorder, how is it possible that the mother's three children each have different phenotypes from one another and different degrees of severity?

Question 52

Chloroplast RNA undergoes _______, which is the alteration of the RNA sequence after transcription.