BIO 101 Assignment Question and Answers (Cytoplasmic Chromosomes)

1. Why can’t cytoplasmic chromosomes be transferred from father to the next generation

Please read before copying I provided two answers both are correct but different wording and extra details so copy only one answer and change some words too to avoid copy work

ANSWER 1

Cytoplasmic chromosomes, like those found in mitochondria, are usually inherited only from the mother. This is because during fertilization, the sperm contributes mainly its nuclear DNA and very little, if any, cytoplasm. Therefore, the offspring receive cytoplasmic genetic material solely from the mother. Reasons for Maternal Inheritance of Cytoplasmic Chromosomes

• Cytoplasmic Contribution: During fertilization, the egg cell (ovum) provides the majority of the cytoplasm, which includes organelles like mitochondria and chloroplasts. The sperm cell contributes primarily nuclear DNA and very little cytoplasm. This means that the cytoplasmic chromosomes are inherited from the mother.
• Mitochondrial DNA: Mitochondria, which contain their own DNA (mtDNA), are passed down through the maternal line. This is because the mitochondria in the sperm are typically destroyed after fertilization, preventing them from contributing to the offspring’s mitochondrial DNA.
• Chloroplast DNA: In plants, chloroplasts also follow a similar pattern of maternal inheritance. For example, in the plant Mirabilis jalapa, the leaf color is determined by chloroplast DNA that is inherited from the mother, as the pollen (male gamete) does not carry chloroplasts.
• Evolutionary Advantage: This mode of inheritance may provide evolutionary advantages, such as ensuring that the offspring have a consistent set of organelles that are well-adapted to the maternal environment. It also helps maintain the integrity of the organelle genomes, as they are subject to different selective pressures compared to nuclear DNA.
• Exceptions: While most organisms exhibit maternal inheritance of cytoplasmic chromosomes, there are exceptions. Some species, like certain plants (e.g., Passiflora), can show biparental inheritance of chloroplasts, but this is not the norm.

In summary, cytoplasmic chromosomes are typically not transferred from father to offspring due to the way fertilization occurs and the roles of the egg and sperm in contributing genetic material. The maternal inheritance pattern ensures that the offspring receive a stable and consistent set of cytoplasmic organelles.

ANSWER 2

Cytoplasmic chromosomes, also known as extranuclear or organelle DNA, are found in structures like mitochondria and chloroplasts (in plants). These chromosomes are inherited almost exclusively from the mother and not from the father. The main reasons why cytoplasmic chromosomes cannot be transferred from the father to the next generation include:

1. Maternal Inheritance of Mitochondria

• In humans and most animals, mitochondria (which contain their own DNA) are passed down from the mother through the egg cell.

• The sperm contributes only nuclear DNA during fertilization, while the mitochondria in the egg become the mitochondria of the offspring.

• Even though sperm cells have mitochondria (to provide energy for movement), these mitochondria are usually destroyed after fertilization.

2. Sperm Mitochondria Are Destroyed

• During fertilization, the sperm’s mitochondria enter the egg but are marked for destruction by a process called ubiquitination.

• The egg has special enzymes that break down the sperm’s mitochondria, preventing them from contributing their DNA to the embryo.

• This ensures that only the mother’s mitochondria are inherited.

3. Prevention of Genetic Conflicts

• If both parents contributed cytoplasmic DNA, there could be conflicts in gene expression, which might cause problems in cell function.

• To maintain stability in inheritance, nature has favored maternal transmission of cytoplasmic DNA.

4. No Cytoplasmic Contribution from the Father

• The sperm mainly contributes nuclear DNA to the offspring, while the cytoplasm (which contains mitochondria) comes from the egg.

• Since the father does not contribute cytoplasm, his cytoplasmic DNA cannot be passed down.

Conclusion

Cytoplasmic chromosomes are inherited from the mother because the egg provides all the necessary organelles, including mitochondria. The sperm’s mitochondria are either excluded from the embryo or destroyed, ensuring that only maternal cytoplasmic DNA is passed to the next generation.