Deck 17: Genomics: Genetics From a Whole-Genome Perspective

Question 1

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

A) heteroplasmic
B) variegated
C) homozygous
D) homoplasmic
E) uniparental

Answer 1

D

Question 2

In certain Latin American countries during periods of political volatility, children were removed from their families and their parents were executed (then referred to as being "disappeared"). The methods with the best chance of reuniting those children with members of their extended family have used mtDNA matching. Why and how?

A) Children's mitochondria will have genomes that are 1/4 identical to each of their grandparents.
B) Children's mitochondria will have genomes that are 1/2 identical to their maternal grandparents.
C) Children's mtDNA will be identical to those of their first cousins.
D) Remains of the children's mothers can be used to match their mtDNA with that of their children.
E) Children's mitochondria will have genomes that are identical to those of their maternal grandmothers.

Answer 2

E

Question 3

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) Mutations of this gene are dominant.
B) Mutations of this gene affect individuals before birth.
C) Interference with translation is not fully rescued by importing lysine from the cytoplasm.
D) Lysine is required in translation of every one of the mitochondrial genes.
E) Homoplastic organelles would be inviable due to failures in translation.

Answer 3

E

Question 4

Chlamydomonas, a unicellular 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 resistant because cpDNA is responsible for the resistant phenotype.
B) Approximately half the progeny are sensitive because cpDNA is responsible.
C) Approximately half the progeny are sensitive because this is the recessive trait.
D) All progeny are sensitive because sensitivity is the dominant trait.
E) All the progeny are sensitive because this is the recessive trait.

Question 5

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) Haploid organelle genomes can replicate to form diploid or polyploidy genomes.
C) Mutant mitochondria replicate at different frequencies than do wild type.
D) Large mitochondria in oocytes can divide into many smaller mitochondria, and smaller mitochondria can replicate their DNA.
E) Somatic cells replicate their nuclear DNA at a faster rate than the oocyte.

Question 6

In Leber's disease (LHON), degeneration of the optic nerve results in blindness due to a defect in NA dehydrogenase affecting electron transport. If this is due to a mutation in a mitochondrial gene, whi combination of the following effects would you expect to see when doing a pedigree analysis of a fa with LHON? i. variable expressivity
Ii) incomplete penetrance
Iii) progressive blindness over time
Iv) maternal inheritance
V) diminished muscle mass

A) ii and iii only
B) i, ii, iii, and iv only
C) iii and iv only
D) i, ii, iii, and v only
E) i and ii only

Question 7

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 egg nucleus may have had one or more mutations that alter mitochondrial function.
B) The somatic cell's mitochondria may have been transferred as well.
C) The egg cell may be heteroplastic before injection.
D) The transferred nucleus may destroy the egg mitochondria.
E) The transferred nucleus may have mutations that are incompatible with the egg cell's mitochondrial function.

Question 8

There is a hypothetical gene in mice that 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. Twitchiness may simply be a dominant trait caused by a nuclear allele, or it could be due to mtDNA. 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 male offspring.
B) Backcross twitchy female offspring with normal fathers.
C) Breed twitchy male progeny with normal females to show no paternal inheritance.
D) Breed twitchy female with twitchy male F1 mice to verify there is maternal inheritance.
E) Sequence the mtDNA of the twitchy mother.

Question 9

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

Question 10

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

A) It is suppressive.
B) It replicates faster than wild type.
C) It has small deletions of mitochondrial DNA.
D) It is a neutral mitochondrial mutation.
E) It is a nuclear or segregational mutation.

Question 11

Giardia is eukaryotic yet is long thought to lack a mitochondira. Recently, researchers have found that each Giardia cell contains double membrane- bound organelles similar to a mitochondria called mitosomes that lack mtDNA. What is the best explanation for mitosomes?

A) Mitosomes are more advantageous to eukaryotes than mitochondria.
B) Mitosomes evolved from another Giardia organelle that lacked DNA.
C) Mitochondria in Giardia evolved into mitosomes and have lost or transferred their DNA to the Giardia nuclear genome.
D) Giardia are asexual and thus do not require mitochondria with its own DNA.
E) Mitosomes are the ancestral form of the mitochondria.

Question 12

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) only those with an affected mother
B) any of the members of this generation
C) any of those affected
D) any of the affected women
E) any of the women

Question 13

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) Mitochondrial variants in people descending from originally small populations show enough diversity to be used to construct an evolutionary tree.
B) The original human population must have grown to be quite large before its members began migrating to other lands and other continents.
C) Nuclear gene sequencing must be used to resolve the question of human ancestral origins.
D) Current human populations must have a much higher mutation rate than ancient populations.
E) A single human population, living about 200,000 years ago, could not have given rise to all current human populations.

Question 14

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 sex are tested for CO2 sensitivity. Which of the following results do you expect?

A) All the offspring are female.
B) All the offspring are sensitive.
C) Only male offspring backcrossed to the female parent are sensitive.
D) All the offspring are sensitive, but only males pass it on.
E) All the offspring are male.

Question 15

The noncoding regions of mammalian mitochondrial genomes have little to no selective pressure. Which of the following are consequences of this condition?

A) a rate of mtDNA repair is much lower than that of nuclear sequences
B) noncoding mitochondrial DNA increases in nucleotide diversity more quickly than coding DNA
C) a rate of mutation that can increase with successive generations in a maternal line
D) a high rate of natural selection for genomes identical to those of the mother
E) a high rate of loss of mitochondrial genomes relative to nuclear sequences

Question 16

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 OMIM description of symptoms and diagnosis
C) the sequence with specifically altered amino acid coding
D) the OMIM description of the TRMU gene at 22q13
E) the Mitomap loci of genes associated with deafness

Question 17

All of the following are evidence in support of the endosymbiotic origin of mitochondria, except?

A) Mitochondiral genetic codes (codons) are related to each other across phyla, and are distinct from nuclear genetic codes.
B) Mitochondria maintain their own DNA.
C) Transcription in mitochondria is performed by an enzyme similar to bacterial RNA polymerase.
D) Yeast cells can live without mitochondria.
E) Mitochondria have a double membrane.

Question 18

The human genome contains DNA that is similar to mtDNA. Some of this DNA shows significant levels of nucleotide divergence from human mtDNA, while other nuclear DNA shows very high levels of nucleotide identity with mtDNA. Which of the following hypotheses best explains these data?

A) Nuclear DNA is older than mtDNA.
B) mtDNA is derived from the nuclear DNA with higher levels of homology.
C) mtDNA has integrated into nuclear chromosomes several times over a long span of time.
D) mtDNA and nuclear DNA share many sequences by chance.
E) Nuclear DNA has a low level of mutation compared to the mtDNA.

Question 19

In 1718, the tsar of Russia, his wife the tsarina, 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 and tsarina only
B) each of the claimants or their living children
C) the tsar, tsarina, and the other assassinated children
D) the tsarina and the claimants
E) the tsar and tsarina and living relatives of each of them

Question 20

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

A) chromosomal duplication mutations
B) chromosomal deletion mutations
C) dominant loss- of- function mutations
D) incomplete penetrance
E) dominant gain- of- function mutations

Question 21

Mitochondrial genome transcription, translation, and replication occur where?

Question 22

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 23

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

Question 24

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

Question 25

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 26

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

Question 27

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

Question 28

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 29

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 30

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 31

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 strR and mt- is strS. Will offspring live or die if they are exposed to streptomycin?

Question 32

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 33

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 34

Chloroplast mRNAs are not 5'- capped or polyadenylated, making them more like RNAs of domain .

Question 35

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

Question 36

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

Question 37

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

Question 38

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

Question 39

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

Question 40

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

Question 41

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

Question 42

The plastids can differentiate into that carry out photosynthesis.

Question 43

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

Question 44

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 45

If the mother and grandmother of a given family both exhibit 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 46

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

Question 47

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

Question 48

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 49

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

Question 50

Explain the distinction between primary and secondary endosymbiosis.

Question 51

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

Question 52

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

Question 53

Contrast the mechanism that gives rise to tortoise- shell cats (a mosaic coat color) with the mechanism that gives rise to variegated plants.?

Question 54

The organelles involved in organelle heredity are and _ .