Origin of Sex and Multicellularity

Question 1

Briefly explain the early history of planet Earth

Answer 1

4.6 billion years ago - Earth is formed by the gravitational accumulation of dust and larger objects and the moon forms during a major collision

> 3.8 billion years ago - Progress continues to be halted due to continued bombardment of large objects that can boil off oceans and atmosphere

< 3.8 billion years ago - Metorite bombardment decreases in inensity and planet starts to cool below threshold of ocean and atmopshere. Organic compounds begin to synthesise and accumulate

3.75 billion years ago - Earth cools to an extent that the crust can start solidifying, oceans and atmopshere could potentially start condensing out

~3.8 billion years ago - have conditions on Earth suitable for life

3.5 billion years ago - earlies fossil evidence for life on Earth

Question 2

How does the early atmopshere form?

Answer 2

Volcanic outgassing of water vapour, N2, CO2, CH4, NH3, H2 and H2S

Question 3

What is slushball Earth?

Answer 3

Increased oxygen and carbon dioxide levels chnaged the atmopshere which caused almost full glaciation of Earth

Some areas had free water due to volcanic acitvity - this is where life continued

Question 4

What is variation due to in asxeual and sexual reproducing species?

Answer 4

Asexual - mutations

Sexual - mutations, independent assortment, crossing over

Question 5

What are the problems with sex?

Answer 5

Disadvantageous from evolutionary perspective

Asexual reproduction is more efficient

In sexual reproducing species, one partner tends to do all the work which makes it less efficient

Question 6

What are the advantages of sexual reproduction?

Answer 6

In asexual, mutations spread rapdily in a population

In sexual, can purge deletious mutations and combine advantegous mutations

Question 7

What are the theories of why sex evolved?

Answer 7

1) A method of adapating to change by evolving faster (unlikely as evolution has no foresight)

2) A method of fending off disease/parasites (unlinkely as evolution has no foresight)

3) A method of repairing genes

4) Historical accident (most reliable)

Question 8

When did sex evolve?

Answer 8

~1.2 billion years ago

Question 9

What early eukaryotes did not sexually reproduce?

Answer 9

Some amoebae and flagellate protists

HOWEVER, some protists can asexually reproduce for generations and then sexually reproduce when environments become unfavourable

Question 10

When did multicellualrity evolve?

Answer 10

~1 billion years ago

Question 11

What advatnage does multicelluarity have?

Answer 11

Division of labour