Question 1

Which of the following best explains why mitochondrial DNA is typically inherited only from the mother in humans?

Accepted Answer

Sperm mitochondria are actively destroyed after fertilization, leaving only maternal mitochondria in the zygote.

Question 2

A woman who is heteroplasmic for a mitochondrial mutation has four children. Which of the following best describes the expected pattern of inheritance for the mutation among her children?

Accepted Answer

Each child may inherit different proportions of mutant and wild-type mitochondria, leading to variable expression.

Question 3

Which of the following observations in a pedigree most strongly suggests a disease is caused by a mitochondrial mutation?

Accepted Answer

The disease is only transmitted by mothers to all of their children, but not by fathers.

Question 4

Which of the following is NOT evidence supporting the endosymbiotic theory for the origin of mitochondria and chloroplasts?

Accepted Answer

They contain introns and linear chromosomes like eukaryotic nuclei.

Question 5

A plant with variegated leaves (green and white patches) is crossed as a female with a green-leafed male. All offspring are variegated. What is the most likely explanation?

Accepted Answer

The trait is due to heteroplasmy in the chloroplast genome inherited maternally.

Question 6

Why do some mitochondrial diseases show incomplete penetrance or pleiotropy?

Accepted Answer

Because the expression of mitochondrial mutations can depend on the proportion of mutant mitochondria (heteroplasmy) and interactions with nuclear genes.

Question 7

Which formula would you use to estimate the probability that a child will inherit a mitochondrial mutation if the mother is heteroplasmic with 40% mutant mitochondria and random segregation occurs?

Accepted Answer

$$P = 0.4$$

Question 8

Which of the following best explains why many genes necessary for mitochondrial function are encoded in the nuclear genome?

Accepted Answer

Because the nuclear genome is more stable and can better regulate gene expression for organelle function.

Question 9

A researcher is tracing maternal ancestry using mitochondrial DNA. Which limitation should they be aware of?

Accepted Answer

Mitochondrial DNA does not recombine, so it cannot distinguish between close maternal relatives.

Question 10

Which of the following scenarios would most likely indicate a gene is located in the mitochondrial genome rather than the nuclear genome?

Accepted Answer

A trait is only inherited from the mother, regardless of the father's genotype.

Question 11

A woman with Leber hereditary optic neuropathy (LHON), a mitochondrial disease, has three children with an unaffected man. Which of the following is the most likely outcome?

Accepted Answer

All of her children will inherit the mutation, but the severity may vary due to heteroplasmy.

Question 12

Which of the following best describes heteroplasmy?

Accepted Answer

The presence of more than one type of organelle genome within a single cell or individual.

Question 13

Which of the following is a real-world application of mitochondrial transplantation?

Accepted Answer

Replacing defective mitochondria in oocytes to prevent transmission of mitochondrial diseases.

Question 14

Which of the following features is shared by both mitochondria and chloroplasts, supporting their bacterial origin?

Accepted Answer

Circular DNA and prokaryote-like ribosomes.

Question 15

A scientist observes that a certain protein required for mitochondrial function is encoded by a nuclear gene. Which evolutionary process best explains this observation?

Accepted Answer

Horizontal gene transfer from the mitochondrion to the nucleus during evolution.

Question 16

Which of the following best explains why mitochondrial diseases can affect multiple organ systems (pleiotropy)?

Accepted Answer

Mitochondria are present in nearly all cell types and are essential for cellular energy production.

Question 17

Which of the following equations best represents the expected proportion of mutant mitochondria in a child if the mother is heteroplasmic with $$x$$ fraction of mutant mitochondria and random segregation occurs?

Accepted Answer

$$P_{mutant} = x$$

Question 18

Which of the following is a limitation of using mitochondrial DNA to determine relatedness between individuals?

Accepted Answer

Mitochondrial DNA does not recombine, so it cannot distinguish between siblings with the same mother.

Question 19

Which of the following best describes the structure of the mitochondrial genome?

Accepted Answer

Circular DNA without histones, similar to bacterial genomes.

Question 20

A family has a history of a disease that is only passed from mothers to all of their children, regardless of sex. Which type of inheritance does this pattern most likely represent?

Accepted Answer

Mitochondrial (maternal) inheritance.

Ch 17: Organelle Inheritance and the Evolution of Organelle Genomes

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