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Evolution of diversity > Genetic evolution > Flashcards

Genetic evolution Flashcards

1
Q

What is polymorphic?

A

A population with more than one allele at a locus

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2
Q

What is monomorphic?

A

A population with only one allele at a locus, allele is fixed.

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3
Q

What is C-value

A

the amount of DNA in a haploid genome

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4
Q

What is the C-value paradox?

A
  • genome size does not correlate with size/complexity of organism
  • e.g. similar species can have very different genome sizes, implying the correlation between genome size and complexity is weak
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5
Q

Does the number of genes correlate with genome size?

A

No.

  • number of genes roughly correlate with complexity of organism, but have no link with genome size
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6
Q

Does amount of non-coding DNA correlate with genome size?

A

Yes.

  • The more non-coding DNA there is, the bigger the genome
  • especially prominent in eukaryotes
  • called ‘junk DNA’
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7
Q

State the procceses the changes genome size

A
  1. Gene duplication and loss (in genic region)
  2. Selfish DNA (in nongenic region)
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8
Q

What are selfish genetic elements (SGEs)?

A
  • Genetic segments that have no obvious function but replicate
  • enhanced transmission relative to the rest of the genome
  • Can be detrimental or neutral to the organism
  • Can be chromosomes, genes, haplotypes etc
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9
Q

what cause the enhanced transmission of SGEs?

A
  • Gonotaxis: orientating towards germline cells
  • interference: scuppering the competition (rother genes)
  • Over-reolication: replicating more than once during cell cycle

SGEs fix rapidly unless opposed by evolutionary forces

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10
Q

What are the effects of selfish DNA on the host?

A

Increase genome size because over-replication

  • No function so not selected against
  • those with function often deleterious to host, so selected against
  • Rarely beneficial to host
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11
Q

What is the neutral thoery of molecular evolution?

A
  • Majority of genetic variants in most populations are selectively neutral (not under selective pressure)
  • Most gene variants confer neither advantage nor disadvantage
  • Neutral varaints must accumulate via genetic drift
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12
Q

What gave rise to the neutral theory of molecular evolution?

A
  • Most populations habour more genetic variation than would be expected if natural selection was the only influence
  • Many mutations don’t alter function of protein
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13
Q

How can molecular mutations be neutral?

A
  • Many nucleotide substitutions have 0 effect on phenotype because most amino acids specified by more than one codon
  • synonyous substituitons: changed nucleotide, same amino acid. Therefore no affect on protein function (may change mRNA stability, translation rates etc.)
  • Less likely influenced by natural selection therefore neutral
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14
Q

What nonsynonymous substitutions?

A
  1. Missense sub: change amino acid
  2. Nonsense sub: mutation encodes stop codon
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15
Q

What are the effects of nonsynonymous substitutions?

A
  • Likely deleterious because change in amino acid seqeunce likely to change protein structure
  • Some neutral because sometimes amino acid repliacement does not alter protein’s shape
  • Some advantageous, enhance protein function
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16
Q

Why do synonymous subs accumulate at much higher rate in protein coding genes than nonsynonymous subs?

A

because most nonsynonymous subs are harmful therefore quickly removed form the population

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17
Q

What are pseudogenes?

A
  • copies of genes that are no longer functional
  • not subject to strong selection so have much higher rate of substitution
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18
Q

Why is the fixation rate of new neutral mutation independent of population size?

A
  • population size = N
  • neutral mutation rate = µ
  • number of new mutations = µ2N (2N copies of genes able to mutate in a population of N individual
  • probability of fixation of a new mutation by drift = 1/2N (probability of fixation equals its initial frequency)
  • Rate of fixation of neutral mutations (m) = µ2N x 1/2N = µ
  • Therefore m = µ (the number of new neutral mutations that will fixate via drift depends solely on mutation rate)
  • Rate of fixation depend on probablity of fixation, which depend on population size –> bigger population = smaller chance for a mutation to fixate
  • but fixation rate also depend on the number of new mutations that have arisen, which depend on population size –> bigger population = more mutations
  • Two factors cancel out
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19
Q

What is the basis of molecular clock?

A

Given constant mutation rate, genes in populations diverge in neutral changes at constant rate. Therefore the extent of differnces in neutral genes can be used to calculate divergence time between spp.

20
Q

Does the neutral theory imply that most mutations do not effect individuals?

A

no.

  • many mutations were never observed because they are lethal/ strongly detrimental, so quickly removed
  • The advantageous mutations are quickly fixed, so does not result in significant variation
21
Q

What are the relative rates of synonymous and nonsynonymous subs of amino acids under neutral selection?

A

Rate of synonymous subs ≈ rate of nonsynonymous subs

22
Q

What are the relative rates of synonymous and nonsynonymous subs of amino acids under positive selection?

A

Rate of nonsynonymous subs > synonymous subs

23
Q

What are the relative rates of synonymous and nonsynonymous subs in amino acids under purifying selection?

A

Rate of synonymous subs < nonsynonymous subs

24
Q

What is the morphological species concept?

A

The assumption that members of the same sp. have the same/similar morphological features

25
Q

What are the pros and cons of the morphological species concept?

A

Pros:

  • useful & practical

cons:

  • little use on cryptic spp.
  • members of the same sp. often don’t look the same e.g. sexual dimorphism
  • phenotypic plasticity: phenotype develops differently in response to a different stimulus
26
Q

What are cryptic spp.

A

spp. that are morphologically nondistinguishable but do not interbreed

27
Q

What is the biological spp. concept?

A
  • two populations are separate spp. if they are unable to interbreed and produce any offspring or any fertile offspring
  • if individuals of a group only reproduce with one another, then that group is a disnict species within which genes combine. It becomes an independent evolutionary lineage
28
Q

Pros and cons of biological spp. concept?

A

Pros

  • Key evolutionary concept for sexual organisms

cons

  • practically difficult, need crossing experiments
  • fuzzy boundaries: e.g. ring spp.
  • Asexual organisms not applicable
29
Q

what is the phylogenetic spp. concept?

A
  • spp. like branches of the tree of life
  • one sp. splits into two decendants spp. which thereafter evolve as distinct lineages
30
Q

Pros and cons of phylogenetic spp. concept?

A

pros

  • allows us to consider spp. over evolutionary time
  • based on evolutionary concept
  • applicable to asexual spp.

Cons

  • arbitary boundaries may cause taxonomic inflation
31
Q

What causes speciation?

A
  1. Geographical isolation
  2. Divergent selection
32
Q

What can cause divergent selection?

A
  • Differences in selective pressure
  • differences in selection of mates
33
Q

What are the different types of speciation?

A
  • Allopatric speciation
  • sympatric speciation
  • parapatric speciation
34
Q

What is allopatric speciation?

A

Speciation that results when a population is seperated by a physical barrier

  • seperated populations diverge by mutation, genetic drift and adaptation to different enviroments
35
Q

What is sympatric speciation?

A

speciation that occurs when two groups of the same species live in the same geographic location, but they evolve differently until they can no longer interbreed and are considered different species

36
Q

What can cause sympatric speciation?

A

Reproductive isolation that originates in a population due to disruptive selection and polyploidy

37
Q

How can disruptive seletion cause speciation?

A

e.g. when individuals with certain genotypes have a preference for distinct microhabitats where mating takes place

38
Q

What is polyploidy?

A

Duplication of sets of chromosomes, can arise through autopolyploidy or allopoploidy

39
Q

What is autopolyploidy?

A

duplication of chromosomes in a single species

40
Q

What is allopolyploidy?

A

Combining of chromosomes of two different spp., which often disrupts normal meiosis, result in chromosomes doubling

41
Q

How can polyploidy give rise to speciation?

A
  • tetraploid and diploid cannot produce fertile offspring
  • tetraploid can produce fertile offspring if mate with other tetraploids or if it self fertilises
  • reproductive isolation created
42
Q

What is parapatric speciation?

A
  • new species evolve in contiguous, yet spatially segregated habitats
  • unequal gene flow
  • non-random mating (mostly mate within same geographical region)
  • different habitats influence the development of different species
  • spp. separated by differences in the same environment.
43
Q

What happens if 2 separated populations re-establish contact?

A
  1. Reproductive isolation evolved, 2 populations coexist as seperate species
  2. still interbreed, hybridise and remain one species
  3. Partial isolation: selection against production invable hybrids leads to reinforcement of prezygotic reproductive isolation (mating preferences diverge due to natural selection)
44
Q

What is host shift speciation?

A
  • micro-allopatry due to parasite or plant-feeding insects mating in differnet hosts/natal plant –> reproductive isolation
  • adaptation to new conditions drives further divergence
45
Q

what is ecological speciation/ecological divergence?

A
  • Genetic divergence of populations driven by adaptation to the different abiotic, biotic enviroments
  • important for sympatric and parapatric speciation because gene flow is possible in these two scenarios
46
Q

What are the conditions best for speciation?

A

Divergent selection with some geographic isolation

47
Q

Why is the occurence sympatric speciation hard to prove

A
  • takes too long to conduct experiment
  • present day sympatry could be secondary contact (two sister species could have diverged allopatrically and re-established contact)

Evolution of diversity (4 decks)

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