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Ecology - Evolution > Evolution - Sex and Reproductive Straegies > Flashcards

Evolution - Sex and Reproductive Straegies Flashcards

1
Q

What are examples of sexual system being different among organisms?

A

Asexual or sexual, self-fertilise or outrcross, hermaphroditic or seperate sexes.

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2
Q

Why is difference in sexual system important?

A

Affects genetic variation of a species.

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3
Q

What is difference in genetic variation based on?

A

Mutation rates, either evolving to an optimal level or the lowest possible level.

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4
Q

What is expected if lowest mutation rates are selected for?

A

Mutations only exist because repair system are as efficient as they can be.

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5
Q

What is expected if optimal mutation rate are selected for?

A

Population lineage experience beneficiial mutations fast enough to adapt to environment.

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6
Q

What does fate of mutator allele depend on in asexual reproduction?

A

Progeny are permanently associated with the mutations they cause, where mutations are more often detrimental than are benefical.

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7
Q

What does fate of mutator allele depend on in sexual reproduction?

A

Recombination in meiosis means mutator allele and benefical mutation would seperate, so cannot hitchike to high frequencies.

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8
Q

What is mutation rate likely to be in sexual populations?

A

Against alleles increasing mutation rates.

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9
Q

What are mutations?

A

Not an adaptaton, only a consequence of imperfect DNA replication due to great cost in fitness.

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10
Q

Sexual Reproduction

A

This is syngamy of two genomes, carried out by gametes, followed by reduction in meiosis then gametogenesis.

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11
Q

Why would increased mutation rate be selected against in sexual reproducing populations?

A

Most mutations are either harmful or neutral.

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12
Q

Why might increased mutation rate be benefical to asexual populations?

A

No recombination for benefical mutations, so can provide the genetic material for adaptation

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13
Q

How can higher mutation rates disadvantage asexual populations?

A

Because there is only one allele, a dominant one cannot mask a recessive.

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14
Q

Doecous

A

This refers to species that individuals are either male or female.

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15
Q

Hermaphroditic

A

Species where one individual can produce both kinds of gametes.

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16
Q

What are the two types of asexual reproduction?

A

Vegetative Propogation
Parthenogenesis

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17
Q

Vegetative Propagation

A

This is asexual plant reproduction method where offspring arise from a group of cell.

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18
Q

Parthenogenesis

A

This is a form of reproduction where an egg can develop into an embryo without fertilization by a sperm.

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19
Q

Why does sex/reproduction exist?

A

Increase of genetic variation.

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20
Q

How is sexual reproduction disadvantageous?

A

Reduce genetic variation
Recombination destroys adaptive combinations of alleles.

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21
Q

How may sex reduce genetic varation?

A

Meiotic recombination where variation occurs may due to randomness resulting in same genotype combinations.

22
Q

How may sex destroy adaptive combinations of alleles?

A

This may be due to the emergence of less fit homozygotes recvessive, opposed to asexual.

23
Q

How does linkage disequilibrium reduce in sexual reproduction?

A

Two-locus recombination of two features that code for increased pollination, sexual reproduction would perturb the progeny(may have dominant trait 1 yet recessive trait 2)

24
Q

Linkage Disequilibrium

A

This describes the inheritance of multiple alleles more-so than predicted by chance, due to genetic linkage.

25
Q

How may genes coding for recombination be naturually selected against?

A

If the current allele frequency of the population was stable, and pertubations harmful.

26
Q

Why did sexual reproduction evolve?

A

Recombination in sex breaks down linkage disequilibrium.

27
Q

Why does sexual recombination break down linkage disequilibirum?

A

Genetic variance maintaince by increasing allele combinations by recombination.

28
Q

Why doesn’t asexuality break down LD?

A

A and B mutations only combined when mutation B arises following mutation A

29
Q

Clonal Interference

A

This is competition between linages due to benfeical mutaitons arising in asexual populations/

30
Q

Directional Selection

A

This is when indivdiuals with traits on one side of the mean in their population survive/reproduce better than those on the other.

31
Q

Stabilizing Slection

A

A seleciton force pushing a population toward the average trait.

32
Q

What is an example of stabilizing selection?

A

If A and B code for large size whilst a and b the opposite, stabilizing sleection may select for intermediate, so Ab and aB in excess.

33
Q

Why is sexual selection benefical in stabilizing selection?

A

If in a fluctuating environment where conditions favour larger body size, it can be created quickly.

34
Q

How might parasitism coevolution favour sex/genetic variation?

A

Host develops phenotype resistance increasing in frequency, a parasite evolves to attack it, where parasite genotypes attacking less common vulnerable genotypes become rare, so become prevalent with higher fitness.

35
Q

What did Curtis Lively’s study on Potamopyrgus antipodarum show?

A

The advantage of sexual reproduction over asexual in the presence of parasites.

36
Q

What was Curtis Lively’s experiment?

A

Infected snails with trematodes, over 7 years asexual clones became rare and rare ones common, where previously abundant clones more susceptible to treamatode than previously rare clones.

37
Q

How is fitness increased in genetic drift?

A

Recombination by seperation of benefical and deletrious mutations.

38
Q

Mullers Ratchet

A

This is the process where in the absence of recombination an accumulation of irreversible deleterious mutations result.

39
Q

Describe mullers ratchet…

A

In asexual populations, generations can only contain more deletrious alleles, where zero-mitation class lost to genetic drift over tim, then one mutation eventually etc etc.

40
Q

What did Sarah Otto propose for the advantage of sex/reproduction?

A

Genetic drift and recurrent mutations allow LD between alleles that enhance fitness and neighbouring sites that lower fitness.

41
Q

Hill-Robertson Effect

A

This says that linkage between sites under selection will reduce overall effectiveness of selection in finite population.

42
Q

What is the hill-robertson effect based on?

A

Genetic linkage, when a benefical and harmful allele are genetically linked, the benefical one is prevented from increasing in frequency.

43
Q

Sex Allocation

A

This is the distribution of an organisms resources to male versus female function.

44
Q

Hypothesis of sex ratio being 1:1

A

Should be expected that females are in higher proportion for more rapid growth.

45
Q

What is fishers theory on the sex ratio?

A

Every individual has a mother and a father, both equally contributing to ancestry of subsequent generations, thus if sex ratio differed in progeny, number of grandchildren differ also.

46
Q

How does fishers theory mathematically explain 1:1 sex ratio?

A

If sex ratio was 0.25, average progeny of 4 per female, average number of progeny sired by a male is 12, so 4 grandchildren through each daughter, yet 12 through each son, with 24 grandchilren.
A mutation favouring 50/50 sex ratio wouldmean 8 through daugter and 24 through son, with 32 total grandchildren.

47
Q

Where has the 50/50 sex ratio been tested?

A

Alexandra Basolas test on Platyfish Xiphophorous has three sex chromosomes(females are XX, WX or WY, whilst males are XY or YY.

48
Q

What did Alexandras experiments show?

A

Four of six possible crosses yield a 0.5 sex ratio, whilst XX and YY yields all sons, and WX and XY yields 0.25 sons.
Two populations of 0.25% and 0.78% sex ratios where within 2 generations, it was 0.5 again.

49
Q

How might female-biased sex ratios emerge?

A

Parasitoid wasps, progeny of few females emerge from a single host, as females sons compete for mates with other females sons.

50
Q

Hamiltons Rule

A

This states that an organism is more likely to behave altruistically if the benefit to the recipient multipled by the degree of relatedness between the two individuals exceeds the cost of the actor.

51
Q

Local Mate Competition

A

This is where males compete with their brothes to fertilse their sisters.

Ecology - Evolution (9 decks)

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