Question

Extranuclear inheritance occurs because a. certain genes are found on the X chromosome. b. chromosomes in the nucleus may be transferred to the cytoplasm. c. some cellular organelles contain DNA. d. the nuclear membrane breaks apart during cell division. e. both a and c.

Short answer

The correct answer is c. some cellular organelles contain DNA.

Step-by-step solution

Understanding Extranuclear Inheritance

Extranuclear inheritance refers to the passing on of genetic material that's located outside the nucleus of a cell. That means excluding processes which are related to nuclear chromosomes.

Checking Each Option

Go through each of the given options and eliminate the options that are related to the nucleus or nuclear chromosomes. Here, option a relates genes found on the X which is a nuclear chromosome and not applicable to extra-nuclear inheritance. Option b talks about a process where chromosomes in the nucleus may be transferred to the cytoplasm. But it is not related to extra-nuclear inheritance as it refers to nuclear chromosomes. Option d is also eliminated because it refers to a process that happens to the nuclear membrane, which is not directly related to the concept of extranuclear inheritance.

Choosing the Correct Answer

Option c states that certain cellular organelles contain DNA, which seems the best fit for explaining extranuclear inheritance as these organelles containing DNA (such as mitochondria and chloroplasts) are not a part of the nucleus. Therefore, the inheritance of these organelles can be classified as extranuclear inheritance. Thus, option c is the correct answer. Option e includes option a in its answer so it can’t be correct either.

Key concepts

Mitochondrial DNA

Mitochondrial DNA, often abbreviated as mtDNA, is an essential component of extranuclear genetics. Unlike the chromosomal DNA found in the nucleus, mitochondrial DNA is found in the mitochondria, the powerhouse of the cell.
Mitochondria generate the energy needed for various cellular functions through a process called oxidative phosphorylation. What makes mtDNA special is that it is passed down maternally, meaning you inherit it almost exclusively from your mother. This occurs because the mitochondria in sperm cells are usually destroyed during fertilization.
Mitochondrial DNA is relatively small and circular, and while it contains fewer genes than nuclear DNA, these genes are crucial. They are involved in energy production and can also play a role in various genetic diseases when mutations occur.
Extranuclear inheritance is highlighted here as the mitochondria, carrying this DNA, showcase the transfer of genetic material independent of the nucleus or its chromosomes.

Chloroplast DNA

Chloroplast DNA resides in the chloroplasts, which are organelles found in plant cells and certain algae. Chloroplasts are best known for their role in photosynthesis—the process by which plants convert light energy into chemical energy.
Similar to mitochondrial DNA, chloroplast DNA is also circular and contains genes that aid the organelle's function, many of which are associated with photosynthetic processes. Chloroplast DNA is typically inherited maternally in most plants, meaning that only the plant's mother contributes chloroplasts to the offspring.
Just like mitochondria, chloroplasts contain their own genetic material, contributing to the concept of extranuclear inheritance. This means that the chloroplasts' genes get passed to the next generation not through the nuclear chromosomes but through this separate DNA. As such, this DNA is crucial for exploring how traits associated with photosynthesis and other plant-specific processes are inherited.

Organelles and Genome Inheritance

Organelles equipped with their own DNA, like mitochondria and chloroplasts, are key players in extranuclear inheritance. This form of inheritance defies the traditional Mendelian understanding that genes are only passed down from nuclear chromosomes. Instead, it sheds light on a more nuanced genetic transmission where maternal lineage often plays a central role.

• Mitochondria and chloroplasts carry their own genetic information.
• They are involved in essential life processes — energy production and photosynthesis respectively.
• Inheritance of these organelles is often maternal, as seen in many organisms.

This extranuclear inheritance can lead to the understanding of various genetic disorders and plant hereditary features.
It also shows us how evolution can preserve different types of genetic encoding, emphasizing that not all genetic traits and influences stem only from nuclear DNA. Ultimately, studies in this area can expand the understanding of cellular functions and evolutionary biology.