Question 1

Which of the following best explains why variegated plants can produce green, white, or variegated offspring when used as the female parent in a cross?

Accepted Answer

Because plastid inheritance is random and only the maternal parent contributes plastids, which may be homoplasmic or heteroplasmic.

Question 2

A plant cell contains both wild-type and mutant chloroplasts. What is the term for this condition?

Accepted Answer

Heteroplasmy

Question 3

In a cross between a variegated female plant and a green male plant, which of the following progeny phenotypes is NOT possible?

Accepted Answer

All progeny are determined by the male parent

Question 4

Which equation best represents the probability ($$P) $$that a daughter cell will be homoplasmic for a mutant organelle genome after random segregation, given $$n$$ organelles and $$k$$ mutant genomes?

Accepted Answer

$$P = \left(\frac{k}{n}\right)^n + \left(1-\frac{k}{n}\right)^n$$

Question 5

Which of the following statements about human mitochondrial DNA (mtDNA) is FALSE?

Accepted Answer

mtDNA undergoes frequent recombination.

Question 6

A pedigree shows a disease that is present in every generation, affects both sexes equally, and is only transmitted by affected mothers. What is the most likely mode of inheritance?

Accepted Answer

Mitochondrial (maternal) inheritance

Question 7

Which of the following best explains incomplete penetrance in mitochondrial diseases such as Leber hereditary optic neuropathy (LHON)?

Accepted Answer

Random segregation of heteroplasmic mitochondria leads to variable mutant:wild-type ratios in different tissues.

Question 8

Which of the following is a practical application of cytoplasmic male sterility (CMS) in agriculture?

Accepted Answer

Producing hybrid seeds without manual removal of male flowers (de-tasseling)

Question 9

Which of the following plastids is primarily responsible for photosynthesis?

Accepted Answer

Chloroplast

Question 10

A plant breeder crosses a CMS (cytoplasmic male sterile) female (rf/rf) with a restorer (Rf/Rf) male. What will be the genotype and phenotype of the progeny?

Accepted Answer

Rf/rf, CMS, male fertile

Question 11

Which of the following best describes the concept of 'replicative segregation' in organellar genetics?

Accepted Answer

Random distribution of organelles during cell division can lead to homoplasmic or heteroplasmic daughter cells.

Question 12

Which of the following is NOT a function of mitochondrial genes?

Accepted Answer

Encoding proteins for photosynthesis

Question 13

Why is human mitochondrial DNA particularly useful for tracing maternal ancestry?

Accepted Answer

It is inherited only from the mother and does not undergo recombination.

Question 14

Which of the following statements about the 'mitochondrial Eve' is correct?

Accepted Answer

She is the most recent common matrilineal ancestor of all living humans.

Question 15

A human disease is caused by a partial loss-of-function allele in mitochondrial DNA. Which of the following is most likely true?

Accepted Answer

The disease may show variable severity depending on the proportion of mutant mitochondria (heteroplasmy).

Question 16

Which of the following best explains why null alleles of most mitochondrial genes are lethal?

Accepted Answer

Mitochondrial genes are essential for oxidative phosphorylation, which is required for cellular energy production.

Question 17

Which of the following scenarios would most likely result in a plant with all white leaves?

Accepted Answer

A homoplasmic mutant plastid genotype inherited from the maternal parent.

Question 18

Which of the following is a key difference between homoplasmic and heteroplasmic cells?

Accepted Answer

Homoplasmic cells have organelles with the same genotype, while heteroplasmic cells have a mixture of organelle genotypes.

Question 19

Which of the following best describes the role of the restorer of fertility (Rf) gene in plant breeding?

Accepted Answer

It is a nuclear gene that restores male fertility in plants with cytoplasmic male sterility.

Organellar Genetics: Inheritance and Function of Chloroplasts and Mitochondria

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