5/ origins of sex and multicellular organisms Flashcards
1
Q
when do acritarchs reach their peak in terms of size and diversity, what happens after
A
- 950-850 Ma
- suffer wane - various extinction events
2
Q
snowball/ slushball earth overview
A
- found glacial deposits suggesting the entire earth was frozen
- too much oxygen and too little co2 and methane
- planet freezes
- slushball > snowball - must have been hot spots life survived
3
Q
what glaciations could produce snowball earth conditions
A
- cryogenian (635-720 Ma), marinoan ice age (635 - 650 Ma), sturtian ice age (660-720 Ma)
4
Q
snowball earth - what is significant about boulder clays representing the glaciations above, within and below
A
- carbonates below have v high c isotope values - these reduce co2, leading to glaciations
- banded iron formations bifs within boulder clays - 1st time in 1.8 billion yrs - 1st time since atmosphere oxygenated
- cap carbonates (above) v low c isotope values due to rapid accumulation/loss of orgaisms and burst of methane that methane that ended glaciation
4
Q
disadvantages of sex
A
- very expensive - fight for resources
- most populations 50/50 males/females. pregnant female is weakened
- inefficient way of increasing pop size
4
Q
outline how sexually reproducing organisms increase variation compared to asexually
A
- asexually: only variation due to mutation
- sexually: variation due to mutation, crossing over, independent assortment
5
Q
advantage of sex
A
- allows beneficial mutations to spread across multiple lineages
- combine advantageous mutations
- shed harmful mutations - only 50% offspring have mutation
- much less likely to happen in same lineage - need multiple mutations
6
Q
why does sex not make sense for evolution
A
- benefits of sex involve foresight - natural selection has no foresight, it works in the here and now
7
Q
outline 4 main theories for why sex evolved
A
- a method of adapting to change by evolving faster (evolution has no foresight)
- method of fending off disease/parasites - same problem as above
- method of repairing genes - aligning chromosomes means radically mutated ones don’t replicate. more credible
- historical accident - ingest member of same species, through engulfment chromosomes line up and divide
8
Q
when did sex evolve by
A
- 1200 Ma probs
- 800 million yrs after 1st euk
9
Q
when did multicellularity evolve, once or multiple times, how, advantages
A
- 1000 Ma
- evolved several times independently in dif groups - protists, plants, animals, fungi
- evolved via experimentation w colony formation
- division of labour
