Adaptations & Traits 4

Question 1

hermaphroditic (2)

Answer 1

• having both male and female sex organs or other sexual characteristics
• majority of plants; minority of animals

Question 2

dioecy (2)

Answer 2

• having the male and female reproductive organs in separate individuals
• minority of plants; majority of animals

Question 3

hermaphroditism: advantages (4)

Answer 3

• easier to find mate; “reproductive insurance”: due to selfing, guaranteed mating
• less genetic mixing when selfing
• all of the population is compatible

Question 4

hermaphroditism: disadvantages (3)

Answer 4

• trade-offs: may not be well specialized for specific male/female reproduction
• inbreeding depression if selfing occurs
• limited to those around them

Question 5

dioecy: advantages (3)

Answer 5

• more genetic mixing
• specialization of male/female reproduction
• avoids inbreeding depression

Question 6

dioecy: disadvantages (2)

Answer 6

• susceptible to extreme sex ratio fluctuations at small N

- only 50% of the population is compatible

Question 7

sexual reproduction

Answer 7

• mating with another individual, leading to the production of genetically mixed offspring

Question 8

asexual reproduction (2)

Answer 8

• production of offspring without mating or genetic mixing

- via tillers, budding or fission, or asexual seeds/eggs

Question 9

despite the diversity in organism reproductive systems, what do the majority of eukaryotes practice (2)

Answer 9

• majority reproduce sexually at least every once in a while

- all living eukaryotes descended from an sexual ancestor that already had the genetic tools for sex

Question 10

asexuality: advantages (4)

Answer 10

• reproduce faster by investing in only one sex
• all of the parent’s genes are passed to the offspring
• no competition for mates
• better able to maintain adaptations

Question 11

sexual reproduction: advantages (2)

Answer 11

• more diverse offspring

- faster adaptation due to higher variance

Question 12

evolutionary enigma of sex

Answer 12

• sexual reproduction evolved early and has been maintained across most eukaryotes, despite substantial costs of sex

Question 13

costs of sex (5)

Answer 13

• cost of producing males
• destruction of favourable gene combinations
• cost of finding a mate
• risk of not finding a mate
• risk of disease transmission during mating

Question 14

enigma of sex: cost of producing males

Answer 14

• by dividing resources between daughters and sons, sexual females should be quickly outcompeted by asexual variants that can invest resources only into reproducing females (all else being equal)

Question 15

enigma of sex: destruction of favourable gene combinations (2)

Answer 15

• mom and dad have good gene combinations as they have lived to produce
• sexually produced offspring could contains mixture of genes from mom and dad that is disadvantageous; why break up good gene combinations?

Question 16

what advantages pay the cost of sex

Answer 16

• sex can generate variation needed by selection through recombination and segregation

Question 17

what are two exceptions to this statement: sex generates variation needed by selection

Answer 17

• sex need not increase variation

- not all variation helps selection

Question 18

in what scenario can sex decrease variation (3)

Answer 18

1. selection occurs that favours homozygous individuals
2. after selection, there are fewer heterozygous individuals
3. where asexuality would preserve this variation, sex reduces the variation in the trait by restoring the frequency of heterozygous individuals

Question 19

in what scenario does variation not help selection (2)

Answer 19

1. selection occurs that favours heterozygous individuals
2. sex restores the frequency of homozygotes, increasing variance in a direction that opposes selection (variation produces low fitness offspring)

Question 20

segration load/recombination load

Answer 20

• the reduction in fitness from sex and recombination unravelling the genetic associations built by past selection

Question 21

modifier genes

Answer 21

• genes that alter a trait of interested

- there are modifier genes for sex and recombination

Question 22

negative epistasis hypothesis for sex (2)

Answer 22

• in fitness interactions (epistasis) among genes were predominantly negative: extreme genotypes would be less fit and less frequent, decreasing genetic variance in fitness through disequilibrium
• sex could restore genetic variance and improve response to selection

Question 23

negative epistasis hypothesis for sex indicate that sex/recombination is favoured only when: (3)

Answer 23

• epistasis is negative, but weak
• little variance in epistasis
• sex/recombination is rare

Question 24

does the negative epistasis hypothesis for sex explain why we have sex?

Answer 24

• no, there are too many limitations

Question 25

Red Queen hypothesis for sex

Answer 25

- sexual reproduction has evolved to increase the rate of adaptation in the face of changing interactions with other species

Question 26

challenge of the Red Queen hypothesis for sex (2)

Answer 26

- as long as there is ample genetic mixing within a population and selection is not too strong, the frequency of sex decreases as a result of the Red Queen - this is because sex mainly breaks apart the fit gene combinations that allowed the parents to survive species interactions (high segregation/recombination load)

Question 27

Red Queen hypothesis for sex indicate that sex/recombination is favoured only when: (3)

Answer 27

- epistasis is weak - sex/recombination is rare - there is strong selection per locus