Exam 19: Cytoplasmic Inheritance and the Evolution of Organelle Genomes

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?

Myoclonal epilepsy and ragged red fiber disease (MERFF)is a human condition named for the ragged red fibers of its skeletal muscle cells and myoclonic epilepsy.Individuals with this disorder have a mutation in a mitochondrial gene for a tRNA,specifically that for lysine.Affected individuals are heteroplastic.Why?

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

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 ________.

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

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

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

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

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?

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?

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?

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

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?

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

Chlamydomonas,although a green alga,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?

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 involved,which of the following would give you the most information?

Mitochondrial genome transcription,translation,and replication occur where?

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

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?

The organelles involved in organelle heredity are ________ and ________.