Lecture 5 - origin of sex & multicellular life Flashcards
What is the early atmosphere formed by?
- volcanic outgassing of water vapour + N2 (and its oxides)
- the water vapour gradually condenses to form the oceans & the H2 is lost into space
What happened 950-850 million years ago?
acritarchs reach theeir zenith in terms of diversity & size
What happened after 850 million years ago?
acritarchs suffer a major wane during various extinction events
What occurred during snowball/slushball Earth?
- atmospheric changes lead to a reduction in the Earth’s temperature
What are the 2 extensive glaciation extending into equatorial latitudes that produce snowball/slushball?
Earth scenarios:
- Cryogenian (635-720Ma)
Marinoan Ice Age (635Ma - 650Ma)
Sturtian Ice Age (660Ma - 720Ma)
What are Boulder clays (representing the glaciation) bound by?
Bound by carbonates & above by cap carbonates
- the carbonates below have exceptionally high C-isotope values (due to continental break up producing narrow seaways with enhance carbon burial). These reduced atmospheric CO2 leads to the glaciation.
- banded iron formations occur within the Boulder clays - for the first time in 1.8 billion years iron accumulates in the oceans
- the cap carbonates have exceptionally low C-isotope values. (Due to rapid accumulation and/or absence or organisms and/or a burst of methane that ended the glaciation)
How does the origin of sex speed up evolution?
via crossing over
What is mitosis?
involved in natural cell division (asexual reproduction) in unicellular organisms and natural cell division in multicellular organisms
What is meiosis?
sexual reproduction in unicellular or multicellular organisms
- in asexually reproducing organisms, the only variation is due to mutation. In sexually reproducing organisms variation is due to mutation, independent assortment & crossing over
What is the problem with sex?
- extremely inefficient, as half of the population are busy for 9 months, whereas half of the population don’t do anything
- extremely inefficient compared to mitosis
What happens if a mutation occurs in mitosis?
it spreads to most of the population
What happens if a mutation occurs during sex?
only half of offspring get it
Why is sex combining with advantageous mutations beneficial?
as it increases chance if survival as well as chance of having reproductive success
Why is it beneficial that sex can shed harmful mutation?
the sexual process allows you to get rid of bad mutations by allowing for reproduction across a wide variety of alleles
What are the 4 main theories regarding why sex evolved?
- a method of adapting to change by evolving faster
- a method of fending off disease/parasites
- a method repairing genes
- historical genes
Why is it unlikely that sex evolved as a method of adapting to change by evolving faster?
as evolution works in the present, therefore it isn’t able to predict future conditions
Why is it unlikely that sex evolved as a method of fending off disease/parasites?
as evolution won’t occur in order to prevent diseases in the future
Why is it unlikely that sex evolved as a method of repairing genes?
as why does repairing genes help you in the here and now
When did sex evolve?
approx. 1.2. billion years - some fossils had sexually reproductive organs
- note that some primitive eukaryotes (some amoebae & flagellate protists) don’t sexually produce
How is life likely to have evolved?
multiple times and in a colony formation
- colonies give a division of labour - different parts have different functions e.g. locomotion, feeding etc.
What is an advantage of multicellular life evolve in colonies?
it has the advantage of division of labour
