Lecture 5: Origin of sex and Multicellular organisms

Question 1

snowball or slush ball earth

Answer 1

when looking at the continental plate arrangement it is clear that glaciers at top, bottom & the equator. Showing planet was once frozen solid = SNOWBALL EARTH. Now accepted must have been SLUSHBALL earth as volcanoes would not have been frozen solid.

Question 2

Glaciations extending into equatorial latitudes producing snowball/slushball Earth Scenarios:

Answer 2

• 765Ma (?confined to Africa)
• 710Ma (global)
• 600Ma (global)
• 542Ma (relatively small)

Question 3

what are boulder clays?

Answer 3

deposit of clay often full of boulders.

They represent glaciations and are bound below by CARBONATES and above by CAP CARBONATES

Question 4

CARBONATES below boulder clays

Answer 4

exceptionally high C-iostope values. (Due to continental break up producing narrow seaways with enhance C burial. These reduced atmosphere CO2 leading to the glaciations)

Question 5

BIFs and boulder clays

Answer 5

bounded iron formations occur with the boulder clays - for the first time in 1.8 billion years iron accumulates in the oceans.

Question 6

CAP CARBONATES above boulder clays

Answer 6

exceptionally LOW C-ISOTOPE VALUES. (due to rapid accumulation an/or absence of organisms &/or a burst of methane [CH4] that ended the glaciations)

Question 7

Mitosis description:

Answer 7

involved in natural cell division [asexual reproduction] in unicellular organisms & natural cell division in multicellular organisms.

Question 8

Mitosis steps:

Answer 8

1) Each chromosome consists of 2 chromatids
2) Chromosome attach to equator of spindle
3) chromatids separate & begin to move apart
4) chromatids drawn to opposite ends of dividing cell
5) = 2 new daughter cells

Question 9

Meiosis description:

Answer 9

sexual reproduction in unicellular or multicellular organisms

Question 10

Meiosis steps:

Answer 10

1) Early meiosis - each chromosome appears single
2) Chromosomes associate into like-sized pairs
3) Each chromosome splits into chromatids
4) Chromosomes separate along the spindle & cell splits
5) 2 new nuclei are formed
6) each daughter cell undergoes a 2nd division, resembling mitosis
7) 4 new daughter cells, each with half number of chromosomes of parent

Question 11

In mitosis the daughter cells are..

Answer 11

identical to the parent as well as to each other.

Question 12

In ASEXUALLY reproducing organisms the only variation is due to..

Answer 12

MUTATION

Question 13

in SEXUALLY reproducing organisms variation is due to..

Answer 13

MUTATION AND CROSSING OVER

Question 14

what % of eukaryotes reproduce sexually

Answer 14

95%

Question 15

what balance of male to female is often expected

Answer 15

50% M 50% F

Question 16

problems with this 50% male & 50% female

Answer 16

in humans e.g.= when female gets pregnant they are ‘useless’ for around a year. Would make more sense to have 10% male and 90% female?

Question 17

Advantages so their isn’t a rate of 10% male and 90% female

Answer 17

• sex can combine advantageous mutations

- sex can shed harmful mutations

Question 18

4 main theories regarding why sex evolved:

Answer 18

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

Question 19

when did sex evolve?

Answer 19

probably by 1,200 Ma

Question 20

Some primitive eukaryotes such as:

Do not:

Answer 20

Amoebae & flagellate protists

do NOT sexually reproduce

Question 21

Origin of multicellular life:

Answer 21

it evolved several times INDEPENDENTLY in different biological groups. (various protist, plants, animals & fungi)
Probably evolved via experimentation with COLONY FORMATION

Question 22

advantage of multicellular life:

Answer 22

Division of labour