6

Question 1

draw a tree diagram for the various reproductive modes of organisms on earth

Answer 1

reproductive system - sexual/asexual
sexual system - hermaphrodite/dioecious
mating system - self fertilisation/cross fertilisation

Question 2

define parthogenesis

Answer 2

asexual reproduction in which an embryo develops from an egg without fertilisation

Question 3

define clonal propagation

Answer 3

asexual reproduction not involving an egg

Question 4

define a hermaphrodite

Answer 4

individual has both male and female reproductive parts.

Question 5

define dioecious

Answer 5

a characteristic of certain species that have distinct unisexual individuals

Question 6

3 characteristics of sexual reproduction

Answer 6

• 2 parents contribute genetic material to offspring
• meiotic, reductive division to form gametes
• fusion of gametes

Question 7

3 characteristics of asexual reproduction

Answer 7

• 1 parent contributes genetic material
• no meiotic reductive division.
• offspring are genetic replicas (clones) of parents

Question 8

give 2 examples of organisms which can reproduce either sexually or asexually

Answer 8

water fleas (daphnia)
water hyacinth (pontederia)

Question 9

two-fold cost of meiosis

Answer 9

• compared to an asexual female, a sexual female contributes only 50% of her gene copies to the next generation
• this transmission bias favours asexuals in competition with sexual females

Question 10

whereas asexual reproduction maintains favourable combinations of alleles, sexual reproduction

Answer 10

can continually recreate unfavourable combinations of alleles

Question 11

list the 6 costs of sex

Answer 11

• time and energy to find and attract mates
• increased energetic costs of mating
• risk of predation and infection
• cost of producing males
• 50% less genetic transmission
• break up of adaptive gene combinations through segregation and recombination

Question 12

state the 2 main benefits of sex

Answer 12

it allows for the bringing together of favourable mutations and the elimination of harmful mutations (independent assortment recombination)

Question 13

what are the benefits of genetic variation in variable/unpredictable environments known as?

Answer 13

lottery models
- tangled bank hypothesis
- red queen hypothesis

Question 14

tangled bank hypothesis

Answer 14

an evolutionary theory that suggests sexual reproduction increases genetic diversity, which is advantageous in complex and variable environments.

Question 15

in what environments is the tangled bank hypothesis applicable?

Answer 15

in spatially heterogeneous environments

Question 16

in what environments is the red queen hypothesis applicable?

Answer 16

in temporally heterogeneous environments

Question 17

red queen hypothesis

Answer 17

an evolutionary theory that suggests species must constantly adapt and evolve in order to survive while competing against other organisms that are also evolving.

Question 18

describe the evening primrose

Answer 18

• 30% of Oenothera species are functionally asexual
• over time, there have been many independent sexual-asexual transitions

Question 19

describe what experiments on asexual Oenothera have shown

Answer 19

asexual oenothera have:
- more premature stop mutations which lead to dysfunctional proteins
- higher rates of protein sequence evolution
- this implies a greater accumulation of deleterious mutations

Question 20

what is the effect of spatial heterogeneity in selection?

Answer 20

it can facilitate the evolution of sex

Question 21

describe what experiments were carried out on the rotifer Brachionus calyciflorus

Answer 21

• planktonic freshwater animal
• facultatively sexual with genetic variation for the propensity to reproduce sexually or asexually
• each population consisted of two subpopulations, with migration performed manually between them
• 10 replicate populations evolved under each of these conditions for ~70 generations

Question 22

draw diagrams for the experiments conducted on rotifer

Question 23

what were the results of experiments conducted on rotifers?

Answer 23

higher rates of sex are maintained in populations evolving in heterogenous habitats:
- sex declined rapidly over 12 weeks (70 generations) in homogeneous environments
- sex persisted at a much higher level with spatial heterogeneity

Question 24

describe the distribution of asexuality by parthenogenesis

Answer 24

- sporadically distributed across the animal kingdom - more common in invertebrates, rare in vertebrates

Question 25

describe the distribution of asexuality by clonal propagation

Answer 25

- much more common in plants - few species (if any) are exclusively asexual

Question 26

why are asexual species usually t the tips of phylogenies?

Answer 26

- macroevolutionary pattern indicates higher extinction rate - low chance of long term evolutionary persistence - probably due to extremely low genetic variation and accumulation of deleterious mutations

Question 27

describe a rare case of ancient asexuality

Answer 27

- bdelloid rotifers - males are unknown - no sex for millions of years

Question 28

outbreeding

Answer 28

mates are less closely related than random

Question 29

inbreeding

Answer 29

mates are more closely related than random

Question 30

in practice, there is a ----- between outbreeding and inbreeding

Answer 30

continuum

Question 31

outcrossing

Answer 31

- mating with someone else either by outbreeding or inbreeding - fusion of gametes from 2 parents, where gametes derive from meiotic reductive division

Question 32

selfing (self-fertilisation)

Answer 32

- mating with yourself - most extreme form of inbreeding - NOT asexual reproduction - fusion of gametes from 1 parent - gametes derive from meiotic reductive division

Question 33

why is there plenty of potential for inbreeding?

Answer 33

- local population substructure enhances mating among relatives - hermaphroditic organisms have the potential for self fertilisation (most plants, many animals) - in small populations, even random mating can lead to mating among relatives

Question 34

describe two inbreeding avoidance traits in flowering plants

Answer 34

1. timing offset between male and female reproduction - pollen vs ovule maturation within a flower - when male vs female flowers open 2. diverse morphological & physiological mechanisms to avoid selfing - self incompatibility - eg spacing of anther and stigma

Question 35

describe inbreeding avoidance behaviours in animals

Answer 35

- dispersal by one sex - delayed maturation - extra pair copulation - kin recognition and avoidance

Question 36

what are the population genetic effects of inbreeding?

Answer 36

- changes genotype frequencies: increases homozygosity, decreases heterozygosity (H) - does not directly change allele frequencies; does not change polymorphism (P)

Question 37

the effect of inbreeding on the rate of heterozygosity decline depends on

Answer 37

mating patterns

Question 38

define inbreeding depression

Answer 38

the reduction in fitness of inbred offspring compared to outcrossed offspring

Question 39

effects of inbreeding depression

Answer 39

- lower viability (survival) - lower fertility (reproductive output) strong inbreeding depression disfavours inbred offspring - thus favouring outcrossed mating systems

Question 40

why can inbreeding reduce fitness?

Answer 40

due to homozygosity of recessive deleterious alleles

Question 41

what can reduce polymorphism?

Answer 41

competition between homozygous genotypes (selection) and genetic drift of small populations

Question 42

describe the transition from inbreeding depression to selfing

Answer 42

- very common - associated with extensive phenotypic evolution - roughly 20% of plants and hermaphroditism animals are highly selfing

Question 43

describe the frequency in nature of selfing and outcrossing in the short term

Answer 43

- if conditions are favourable selfing can spread via natural selection -> lack of reproductive assurance due to rarity of pollinators or mates -> transmission advantage from self and exported pollen -> low inbreeding depression - but harmful effects of inbreeding depression encourage outcrossing

Question 44

describe the frequency in nature of selfing and outcrossing in the long term

Answer 44

- selfing leads to low diversity and inefficient selection - can drive higher extinction rates in selfing species - macroevolutionary pattern of greater prevalence of outcrossing

Question 45

describe the theory of automatic selection of a selfing gene by R.A fisher

Answer 45

table - selfing variant has a transmission advantage