Lecture 5 - origin of sex & multicellular life

Question 1

What is the early atmosphere formed by?

Answer 1

• volcanic outgassing of water vapour + N2 (and its oxides)
• the water vapour gradually condenses to form the oceans & the H2 is lost into space

Question 2

What happened 950-850 million years ago?

Answer 2

acritarchs reach theeir zenith in terms of diversity & size

Question 3

What happened after 850 million years ago?

Answer 3

acritarchs suffer a major wane during various extinction events

Question 4

What occurred during snowball/slushball Earth?

Answer 4

• atmospheric changes lead to a reduction in the Earth’s temperature

Question 5

What are the 2 extensive glaciation extending into equatorial latitudes that produce snowball/slushball?

Answer 5

Earth scenarios:
- Cryogenian (635-720Ma)

Marinoan Ice Age (635Ma - 650Ma)
Sturtian Ice Age (660Ma - 720Ma)

Question 6

What are Boulder clays (representing the glaciation) bound by?

Answer 6

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)

Question 7

How does the origin of sex speed up evolution?

Answer 7

via crossing over

Question 8

What is mitosis?

Answer 8

involved in natural cell division (asexual reproduction) in unicellular organisms and natural cell division in multicellular organisms

Question 9

What is meiosis?

Answer 9

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

Question 10

What is the problem with sex?

Answer 10

• 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

Question 11

What happens if a mutation occurs in mitosis?

Answer 11

it spreads to most of the population

Question 12

What happens if a mutation occurs during sex?

Answer 12

only half of offspring get it

Question 13

Why is sex combining with advantageous mutations beneficial?

Answer 13

as it increases chance if survival as well as chance of having reproductive success

Question 14

Why is it beneficial that sex can shed harmful mutation?

Answer 14

the sexual process allows you to get rid of bad mutations by allowing for reproduction across a wide variety of alleles

Question 15

What are the 4 main theories regarding why sex evolved?

Answer 15

1. a method of adapting to change by evolving faster
2. a method of fending off disease/parasites
3. a method repairing genes
4. historical genes

Question 16

Why is it unlikely that sex evolved as a method of adapting to change by evolving faster?

Answer 16

as evolution works in the present, therefore it isn’t able to predict future conditions

Question 17

Why is it unlikely that sex evolved as a method of fending off disease/parasites?

Answer 17

as evolution won’t occur in order to prevent diseases in the future

Question 18

Why is it unlikely that sex evolved as a method of repairing genes?

Answer 18

as why does repairing genes help you in the here and now

Question 19

When did sex evolve?

Answer 19

approx. 1.2. billion years - some fossils had sexually reproductive organs
- note that some primitive eukaryotes (some amoebae & flagellate protists) don’t sexually produce

Question 20

How is life likely to have evolved?

Answer 20

multiple times and in a colony formation
- colonies give a division of labour - different parts have different functions e.g. locomotion, feeding etc.

Question 21

What is an advantage of multicellular life evolve in colonies?

Answer 21

it has the advantage of division of labour