2: The evolution of sex

Question 1

Describe the paradox of sex

Answer 1

• Physiological costs of meiosis (mitosis super quick)
• Asexul repro much quicker!
• Risk of maladapted offspring
• Cost of mating (e.g finding a mate, STIs, increased predation risk)

Question 2

Describe the 2-fold cost of sex

Answer 2

• Sexual repro produces offspring with only 50% of females genome (compared to asexul which is 100%)
• Per gen, sexual female only gets HALF of repro fitness compared to the asexual female

Question 3

Briefly describe the study on New-Zealand mud snails and what this shows about the cost of sex

Answer 3

• NZ mud snails have both asexual and sexual populations
• They created a stable, predator free environ with 30% asexual snails (1st gen)
• In the second gen there were 1.6x more asexual snails

= confirms than in a stable (predator free) environ, sexual reproduction is costly

Question 4

Why is selection weaker in asexual populations?

Answer 4

No recombination

Question 5

Describe background selection (in asexual population)

Answer 5

• Selection against strongly deleterious mutations
• And so in the ‘background’ theres fixation of weakly deleterous mutations

Question 6

Describe Muller’s rachet
(In asexual population)

Answer 6

• Stochastic loss of mutation-free chromosomes)
• Accumulation of deleterous mutations
  → ‘ratchet’ only goes in one direction, pop can never go back to having few deleterious

Question 7

Describe genetic hitchhiking
(in asexual populations)

Answer 7

• Selection for strongly beneficial mutations
• Hitchhiking of linked deleterious mutations

Question 8

Describe Ruby in the Rubbish
(in asexual populations)

Answer 8

• Selection against strongly deletrious mutations
• Elimination of linked beneficial mutations