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Exam 19: Cytoplasmic Inheritance and the Evolution of Organelle Genomes

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Question 1

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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.

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Question 2

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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

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Question 3

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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?

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?

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

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

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?

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

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

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

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?

Mitochondrial genome transcription, translation, and replication occur where?

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?

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?

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?

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

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

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

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?

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?