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Ch. 9 - Extranuclear Inheritance
Klug - Concepts of Genetics 12th Edition
Klug12th EditionConcepts of Genetics ISBN: 9780135564776Not the one you use?Change textbook
All textbooksKlug 12th EditionCh. 9 - Extranuclear InheritanceProblem 20b
Chapter 9, Problem 20b

Payne, B. A. et al. (2013) present evidence that a low level of heteroplasmic mtDNA exists in all tested healthy individuals.
What genetic conditions within a given mitochondrion are likely to contribute to such a variable pool of mitochondria?

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1
Understand the concept of heteroplasmy: Heteroplasmy refers to the presence of more than one type of mitochondrial DNA (mtDNA) within a single cell. This can result from mutations in mtDNA, leading to a mixture of normal and mutated mtDNA molecules.
Recognize the role of mitochondrial replication and segregation: Mitochondria replicate independently of the cell cycle, and their DNA is randomly distributed during cell division. This random segregation can lead to variability in the proportion of mutated and normal mtDNA in different cells.
Consider the impact of mtDNA mutations: Mutations in mtDNA can arise due to errors in replication or damage from reactive oxygen species. These mutations can accumulate over time, contributing to the heteroplasmic pool.
Acknowledge the bottleneck effect: During the development of oocytes (egg cells), a small subset of mitochondria is selected to populate the next generation. This bottleneck effect can amplify or reduce the proportion of mutated mtDNA, leading to variability in heteroplasmy levels.
Factor in selective pressures: Certain mutations in mtDNA may confer a selective advantage or disadvantage to mitochondria, influencing their replication and survival. This can further contribute to the variability in the mitochondrial pool within a cell or individual.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Heteroplasmy

Heteroplasmy refers to the presence of more than one type of mitochondrial DNA (mtDNA) within a single cell or individual. This condition can arise from mutations in mtDNA, leading to a mixture of normal and mutated genomes. The level of heteroplasmy can vary among tissues and individuals, influencing mitochondrial function and health.
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Mitochondrial DNA (mtDNA)

Mitochondrial DNA is the genetic material found in mitochondria, the energy-producing organelles in cells. Unlike nuclear DNA, mtDNA is inherited maternally and is circular in structure. Variations in mtDNA can affect cellular energy production and are linked to various genetic disorders, making its study crucial in understanding mitochondrial function and disease.
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Mitochondrial Dynamics

Mitochondrial dynamics encompass the processes of mitochondrial fusion and fission, which regulate the shape, size, and number of mitochondria within a cell. These processes are essential for maintaining mitochondrial function, quality control, and distribution during cell division. Variations in these dynamics can lead to a heterogeneous population of mitochondria, contributing to the observed heteroplasmy.
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Related Practice
Textbook Question

Researchers examined a family with an interesting distribution of Leigh syndrome symptoms. In this disorder, individuals may show a progressive loss of motor function (ataxia, A) with peripheral neuropathy (PN, meaning impairment of the peripheral nerves). A mitochondrial DNA (mtDNA) mutation that reduces ATPase activity was identified in various tissues of affected individuals. The accompanying table summarizes the presence of symptoms in an extended family.

How can some individuals in the same family show such variation in symptoms? What term, as related to organelle heredity, describes such variation?

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Textbook Question

Researchers examined a family with an interesting distribution of Leigh syndrome symptoms. In this disorder, individuals may show a progressive loss of motor function (ataxia, A) with peripheral neuropathy (PN, meaning impairment of the peripheral nerves). A mitochondrial DNA (mtDNA) mutation that reduces ATPase activity was identified in various tissues of affected individuals. The accompanying table summarizes the presence of symptoms in an extended family.

In what way does a condition caused by mtDNA differ in expression and transmission from a mutation that causes albinism?

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Textbook Question

Payne, B. A. et al. (2013) present evidence that a low level of heteroplasmic mtDNA exists in all tested healthy individuals.

What are two likely sources of such heteroplasmy?

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Textbook Question

The mtDNA accumulates mutations at a rate approximately ten times faster than nuclear DNA. Thus geneticists can use mtDNA variations as a 'molecular clock' to study genetic variation and the movement of ancestral human populations from Africa to different areas of the world more than 125,000 years ago. Propose an explanation for how an analysis of mtDNA can be used to construct family trees of human evolution.

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Textbook Question

Because offspring inherit the mitochondrial genome only from the mother, evolutionarily the mitochondrial genome in males encounters a dead end. The mitochondrial genome in males has no significant impact on the genetic information of future generations. Scientists have proposed that this can result in an accumulation of mutations that have a negative impact on genetic fitness of males but not females. Experiments with Drosophila support this possibility. What experimental data or evidence would you want to evaluate or consider to determine if an accumulation of mtDNA mutations negatively impacts the fitness of males of any species?

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