evidence for several origins Flashcards
Why are viruses considered obligate parasites, and how does this relate to the evolution of cells?
Viruses are obligate parasites because they cannot reproduce without a host cell. This suggests that cells must have evolved first, as viruses depend on the machinery of cells for replication.
What is the progressive hypothesis for the origin of viruses?
The progressive hypothesis suggests that viruses evolved from cell components, such as retrotransposons, which are genetic elements in eukaryotic genomes that can replicate and insert into chromosomes, similar to how retroviruses work.
How does retrotransposons support the progressive hypothesis for the origin of viruses?
Retrotransposons are genetic elements in cells that copy and insert themselves into the host genome, similar to how retroviruses work. This suggests that retroviruses could have evolved from retrotransposons.
What is the regressive hypothesis for the origin of viruses?
The regressive hypothesis suggests that viruses evolved from cells by losing cell components, becoming more parasitic over time, losing essential functions like respiration and protein synthesis, as seen in some bacteria and viruses.
How does the diversity of virus complexity support the regressive hypothesis?
The diversity in viral complexity (e.g., polio vs. smallpox and mimivirus) suggests that viruses may have evolved from bacteria by losing functions over time. Some viruses are simple while others, like mimivirus, are larger and more complex, retaining some self-reliance.
What evidence supports the idea that viruses may have originated from intraparasitic bacteria?
Some bacteria, like Chlamydia, are parasitic and have lost essential functions over time, suggesting that viruses may have originated from bacteria that became intraparasitic, losing functions like respiration and protein synthesis.
How can the diversity of viruses be explained by multiple evolutionary origins?
The progressive and regressive hypotheses both offer ways to explain viral diversity. Viruses may have originated through different routes, and their shared features could be due to convergent evolution, where similar traits evolve for functional reasons rather than from a common ancestry.
