Cycle 1 - Evolution Flashcards
Why are viruses not generally considered to be “alive”?
Qualities of life:
- Reproduction –> viruses require host cell for this
- Make Energy for Itself –> requires host cell
- Maintain –> is not a cell/has no cells
- Evolution –> the only quality the virus does have
Why are viral infections usually difficult to treat with drugs?
- They hide inside of the cells, sometimes dormant
- Use host machinery, no unique virus machinery to target
- So, kill virus = kill host
Hypotheses for the evolutionary origin of viruses
Virus-First Model
- Viruses so much simpler than cellular life, must have evolved first. So, they are older than the oldest simple cell organisms
Escape Hypothesis
- Viruses evolved after cells did, within the cells’ own genes. Our genomes contain DNA pieces that can copy and paste themselves. If one piece was able to mutate, escape and make a coat of protein, it could become a virus.
Giant Virus Model/Regressive Model
- Mimivirus – largest virus, 750 nm
- Has more genes than the average virus, some that code for protein which viruses shouldn’t be able to do and are useless
- Scientists think the genes are leftovers from when viruses were free-living, but then they developed a symbiotic relationship with another organism, becoming more parasitic and losing complexity
Regressive Model (Counter)
- Extra genes in mimivirus are just random leftovers picked up from its hosts over time
How do viral mutation rate affect the prospects for drug design and vaccine development?
Retroviruses (ex., HIV) that can be targeted by antiviral medication have high mutation rates, thus there is a high chance of a random resistant mutation which will be favoured. Thus, natural selection causes the population to evolve resistence quickly.
Why is the effectiveness of anti-viral drugs likely to decrease over time?
Large populations with high chance of mutation resistance due to high mutation rates = high chance of resistant mutation forming and then being acted upon by natural selection
State the principles of natural selection
- Heritable variation, meaning traits must be able to be passed on
- High rate of population growth, meaning there is competition thus selection
- Non-random reproduction or survival, thus advantages are favoured
- Advantageous mutation increases fitness and is passed on
- Change in genotype of the population is the result
Explain the rationale of drug cocktails
The likelyhood that a virus will become resistant to several drugs is slim, but just one drug is practically guaranteed due to the high mutation rates of retroviruses.
Describe the evolutionary origins of HIV
- SIV (chimpanzees have it, from Africa) (zoonotic)
- The genetic information of SIV is compared to HIV, very similar, likely originated from SIV
- Spill over event to humans
- Most mutagenic due to reverse transcriptase (no proofreading), thus it is difficult to develop a vaccine since it changes so much
Define epidemic, endemic, pandemic and zoonotic diseases
- Zoonotic: harmless in original species, spill over to humans
- Endemic: always present in species/area (e.g. SIV)
- Epidemic: rapid spread of a disease but still contained
- Pandemic: large-scale, global epidemic disease
What makes a theory a theory?
How can you tell something is falsifiable?
Theories are broad and must be falsifiable.
- “All X are Y” –> falsifiable
- “Some x are y” –> not falsifiable
- Ex., “There are 10 bones in the body” (falsifiable) vs. “God is real” (unfalsifiable)
- One can be proved wrong, the other cannot be proved right or wrong
Describe “scala naturae” thinking
- Scala natura –> placing things into a ladder-like structure from most to least perfect
- This is not compatible with evolution, as if we all began from a common ancestor, we have all spent the same amount of time evolving and are all adapted to our environments, so it cannot be said that one species is more highly evolved/perfect than another
Describe evidence from geology and the fossil record, the geographic distribution of species, and comparative morphology, that supports the idea of descent from a common ancestor
- Geology: earth slowly changes over time, why doesn’t life? Marine fossils on mountains
- Fossil record: fossils were found of non-living creatures of the time –> resembled living species
- Distribution of species: species on island most similar to nearest constant, no terrestrial animals on islands (only those that could fly and swim were found)
- Comparative morphology: similar body shapes, different uses (ex., bat wings and human arms), also vestigial structures
What are homologous traits?
- Homologous structure: is an example of an organ or bone that appears in different animals, demonstrating descent from a common ancestor
- Ex., arm of a human, wing of a bat, the leg of a dog and the flipper of a dolphin
Why are mutations important to evolution?
The ultimate source of all genetic variation is mutation. Mutation is important as the first step of evolution because it creates a new DNA sequence for a particular gene, creating a new allele.
Prove each statement wrong
- Evolution and natural selection are the same thing
- Evolution occurs slowly
- Selection acts on individuals so individuals evolve
- Natural selection is directed
- Evolution by natural selection is a random process
- Selection acts on the genotype because that is what is inherited
- Natural selection is a major mechanism but several things can result in evolution
- Bacteria and viruses can evolve quickly
- Individuals cannot change, what changes is the makeup of the population over time
- No, there is no guidance, rather random mutations that may be advantageous in the environment
- Mutations are random, but they are influenced by the environment (natural selection is not random)
- Selection is based on the phenotype (the actual traits) not the genotype
