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BIO120 > Lecture 6 > Flashcards

Lecture 6 Flashcards

1
Q

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

A

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

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2
Q

define parthogenesis

A

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

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3
Q

define clonal propagation

A

asexual reproduction not involving an egg

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4
Q

define a hermaphrodite

A

individual has both male and female reproductive parts.

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5
Q

define dioecious

A

a characteristic of certain species that have distinct unisexual individuals

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6
Q

3 characteristics of sexual reproduction

A
  • 2 parents contribute genetic material to offspring
  • meiotic, reductive division to form gametes
  • fusion of gametes
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7
Q

3 characteristics of asexual reproduction

A
  • 1 parent contributes genetic material
  • no meiotic reductive division.
  • offspring are genetic replicas (clones) of parents
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8
Q

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

A

water fleas (daphnia)
water hyacinth (pontederia)

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9
Q

two-fold cost of meiosis

A
  • 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
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10
Q

whereas asexual reproduction maintains favourable combinations of alleles, sexual reproduction

A

can continually recreate unfavourable combinations of alleles

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11
Q

list the 6 costs of sex

A
  • 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
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12
Q

state the 2 main benefits of sex

A
  • favourable combinations of mutations are brought together more rapidly by sex
  • it allows for the bringing together of favourable mutations and the elimination of harmful mutations (independent assortment recombination)
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13
Q

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

A

lottery models
- tangled bank hypothesis
- red queen hypothesis

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14
Q

tangled bank hypothesis

A

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

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15
Q

in what environments is the tangled bank hypothesis applicable?

A

in spatially heterogeneous environments

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16
Q

in what environments is the red queen hypothesis applicable?

A

in temporally heterogeneous environments

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17
Q

red queen hypothesis

A

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

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18
Q

describe the evening primrose

A
  • 30% of Oenothera species are functionally asexual
  • over time, there have been many independent sexual-asexual transitions
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19
Q

describe what experiments on asexual Oenothera have shown

A

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

20
Q

what is the effect of spatial heterogeneity in selection?

A

it can facilitate the evolution of sex

21
Q

describe what experiments were carried out on the rotifer Brachionus calyciflorus

A
  • 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
22
Q

draw diagrams for the experiments conducted on rotifer

A
23
Q

what were the results of experiments conducted on rotifers?

A

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

24
Q

describe the distribution of asexuality by parthenogenesis

A
  • sporadically distributed across the animal kingdom
  • more common in invertebrates, rare in vertebrates
25
Q

describe the distribution of asexuality by clonal propagation

A
  • much more common in plants
  • few species (if any) are exclusively asexual
26
Q

why are asexual species usually t the tips of phylogenies?

A
  • 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
27
Q

describe a rare case of ancient asexuality

A
  • bdelloid rotifers
  • males are unknown
  • no sex for millions of years
28
Q

outbreeding

A

mates are less closely related than random

29
Q

inbreeding

A

mates are more closely related than random

30
Q

in practice, there is a —– between outbreeding and inbreeding

A

continuum

31
Q

outcrossing

A
  • mating with someone else either by outbreeding or inbreeding
  • fusion of gametes from 2 parents, where gametes derive from meiotic reductive division
32
Q

selfing (self-fertilisation)

A
  • mating with yourself
  • most extreme form of inbreeding
  • NOT asexual reproduction
  • fusion of gametes from 1 parent
  • gametes derive from meiotic reductive division
33
Q

why is there plenty of potential for inbreeding?

A
  • 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
34
Q

describe two inbreeding avoidance traits in flowering plants

A
  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
35
Q

describe inbreeding avoidance behaviours in animals

A
  • dispersal by one sex
  • delayed maturation
  • extra pair copulation
  • kin recognition and avoidance
36
Q

what are the population genetic effects of inbreeding?

A
  • changes genotype frequencies: increases homozygosity, decreases heterozygosity (H)
  • does not directly change allele frequencies; does not change polymorphism (P)
37
Q

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

A

mating patterns

38
Q

define inbreeding depression

A

the reduction in fitness of inbred offspring compared to outcrossed offspring

39
Q

effects of inbreeding depression

A
  • lower viability (survival)
  • lower fertility (reproductive output)

strong inbreeding depression disfavours inbred offspring
- thus favouring outcrossed mating systems

40
Q

why can inbreeding reduce fitness?

A

due to homozygosity of recessive deleterious alleles

41
Q

what can reduce polymorphism?

A

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

42
Q

describe the transition from inbreeding depression to selfing

A
  • very common
  • associated with extensive phenotypic evolution
  • roughly 20% of plants and hermaphroditism animals are highly selfing
43
Q

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

A
  • 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
44
Q

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

A
  • selfing leads to low diversity and inefficient selection
  • can drive higher extinction rates in selfing species
  • macroevolutionary pattern of greater prevalence of outcrossing
45
Q

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

A

table
- selfing variant has a transmission advantage

46
Q
A

BIO120 (16 decks)

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