Lecture 9: The evolution of sex

Question 1

all organisms reproduce but reproduction

Answer 1

doesnt always mean SEX –> ASEXUAL REPRODUCTION ACC MAKES MORE SENSE

Question 2

Asexual reproduction:

Answer 2

Mitosis–>
a copying process
-easy, error free and simply
(IPMAT)

Question 3

Sexual reproduction:

Answer 3

2 haploid gametes fuse to form diploid zygote

• involves meiosis
• & therefore recombination & segregation

Question 4

meiosis and unicelular organisms

Answer 4

zygote undergoes meiosis directly

Question 5

the paradox of sex:

Answer 5

-inefficient, complicated and time consuming (meiosis take longer than mitosis)

• difficult & dangerous
• -exposing urself to predators whilst searching for mate
• costly
• -Sexual selection
• -twofold cost of sex

Question 6

two fold cost of sex is aka the cost of males

Answer 6

• john maynard smith
• recognised production of males entails a cost
• asexual female, producing same as a sexual, enjoys a 2fold adv.
• no reproduction potential wasted on sons
• also cost of meiosis, only then genetically half of offspring

Question 7

parthenogenic females produce

Answer 7

only females, who produce more females

Question 8

assumptions of the twofold cost of sex

Answer 8

1) every female produces an equal number of offspring
2) no differential survival
- For sex to evolve, at least on elf these must be violated

Question 9

consequences of recombination for population genetics: sexual recombination creates

Answer 9

sexual recombination creates new & destroys existing gene combinations, whether they are good or bad

Question 10

consequences of recombination for population genetics: recombinatnio can bring together beneficial mutation that arose ____ in different organisms, in an asexual population…

Answer 10

independently

• in an asexual population the same genotype could only be created if the second mutation occurs in a genotype already carrying the first
• THIS IS UNLIKELY
• -therefore SEX can speed up evolution

Question 11

recombination can also reveal

Answer 11

hidden variation , improving the response to selection (in absence of sex this would remain hidden)

Question 12

2 main popular genetic models which help explain the long term benefits of sex

Answer 12

1) Genetic drift - Mullers Ratchet

2) Selection in a changing environment - Red Queen Hypothesis

Question 13

Mullers ratchet 1964

Answer 13

• mutation and genetic drift create problems that sex can solve
• Asexual females must pass on ALL deleterious mutations
• -so number of deleterious can only increase
• recombination means sexual females may not transfer the deleterious mutation & an optimal genotype lost by drift cane reconstructed by recombination

Question 14

Red queen hypothesis:

Answer 14

• sex evolved because recombination brings together novel genotypes with potentially higher fitness, promoting evolutionary adaption
• in unpredictable environments any single genotype mightn’t be universally successful
• QUICK ADAPTIONS (HIGHER CHANCE OF) TO CHANGING ENVIRO

Question 15

red queen hypothesis:: 2 assumptions

Answer 15

• recombination increases the rate of adaption

- some novel genotypes have high fitness

Question 16

Red Queen hypothesis: Assumption; recombination increases the rate of adaption DR

Answer 16

Goddard et al 2005

• effect of sex on the efficacy of NS in yeast
• used yeast as when with sufficient nutrients yeast reproduces ASEXUALLY, but if starved they undergo meiosis = spores equivalent to gametes
• created ASEXUAL yeast strain by deleting 2 genes needed for meiosis
• in HARSH conditions SEXUAL had higher growth rate 94% compared to 80%

Question 17

Red Queen: Assumption novel genotypes have high fitness

Answer 17

• looked at in parasite & host interaction (infection & resistance directed towards the most common genotypes - negative F-d selection)
• parasite 1&2 in population
• shifting of selection,as one parasite becomes more common resistance towards this increases, so then the other becomes more common

Question 18

main difference between sex and asex is

Answer 18

meiosis (recombination & segregation)

Question 19

sexual reproduction has twofold costs but is prevalent in

Answer 19

higher organisms

Question 20

recombination has several beneficial effects:

Answer 20

-pruging of deleterious alleles (muller’s ratchet)
-creating new gene combinations (Red queen)
-