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BIO1334 Genetics > Evolution > Flashcards

Evolution Flashcards

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Biology 101 flashcards
1
Q

Give the 4 postulates of evolution by natural selection.

A
  • individuals within species are variable
  • some of the variations are passed onto offspring
  • in most generations, more offspring are produced than can survive
  • survival and reproduction are not random; individuals with the highest reproductive success are those with the most favourable variations
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2
Q

What does natural selection produce?

A

Descent with modification.

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3
Q

Describe how natural selection produces descent with modification.

A

Evolution occurs because of changes in allele frequencies
The fittest genotype vary from population to population
Divergence of populations leads to speciation

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4
Q

How is evolution considered?

A

In terms of changes in allele and gene frequencies over time, the average action of selection on genotypes.

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5
Q

What does genotypic variation promote?

A

Phenotypic variation.

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6
Q

What does selection remove?

A

Less fit variants.

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7
Q

When rare, recessive alleles are mostly present in…, and how does this effect their selection?

A

heterozygotes, making selection against them negligible & so rare alleles tend to persist.

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8
Q

How does genetic drift affect allele variation?

A

Leads to gain or loss of alleles.

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9
Q

Give the definition of drift.

A

The chance difference in transmission of alleles leading to fluctuations in allele frequency.

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10
Q

Describe the effect of drift.

A
  • most strongly affects rare alleles
  • greater influence on rare alleles than selection
  • primary mechanism for increasing rare recessive alleles
  • responsible for changing frequencies of natural mutations
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11
Q

What is the founder effect?

A

drift in small populations can produce biased allele frequencies.

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12
Q

Give the 3 types of balancing selection.

A
  • heterozygote advantage
  • frequency dependent selection
  • fluctuating selection
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13
Q

Describe heterozygote advantage.

A

eg sickle shaped red blood cells is maintained by balancing selection in humans of Africa & India due to its resistance to the malaria parasite.

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14
Q

Describe frequency dependent selection.

A

alleles only have an advantage when rare, eg predators develop a search image for snails of a certain colour, the uncommonly coloured snail survives.

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15
Q

Describe fluctuating selection.

A

in unstable changeable environments selection may favour opposing phenotypes/alleles over short timescales, eg beak size in different years (wet vs dry).

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16
Q

What does fitness measure? Give the eqn.

A

reproductive success of a genotype relative to the optimum genotype
W = 1 – s

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17
Q

When s is high, allele frequencies…

A

change rapidly.

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18
Q

Describe the adaptive landscape in multidimensional allele space

A
  • natural selection tends to move populations towards the peaks of hills
  • since the environment changes and adaptive peaks shift, the populations follow a never-ending evolution.
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19
Q

Define stabilizing selection.

A

-intermediate variants are selected for, reduces variance of trait.

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20
Q

Define directional selection.

A

-individuals at 1 extreme are selected for, shifts the mean value of a trait, associated with changing environments.

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21
Q

Define disruptive selection.

A

-individuals at both extremes are selected for, leading to a bimodal distribution, associated with sympatric speciation within a population.

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22
Q

How do bizarre traits evolve?

A
  • competition for mates (increasing reproductive success)

- differences in investment of males and females

23
Q

Define kin selection.

A

changes in gene frequency across generations driven by interactions between related individuals.

24
Q

Give the coefficient of relatedness.

A

R = (1/2)^n

25
Q

If: cost of not reproducing / benefit of helping kin reproduce < relatedness then….

A

you should help your kin, will increase your inclusive fitness.

26
Q

How can genes be used to infer phylogenies?

A
  • compare gene sequence or predicted protein sequence with database sequences
  • eg BLAST or GenBank
  • need to look at homologous genes
  • given a constant mutation rate we can infer when sequences diverged
27
Q

Define molecular clocks.

A

estimate the timing of events on trees
Calibrate timings to fossil record and measured rates of mutation
Selective pressure, generation times and oogenesis vs spermatosis
can affect what rate the clocks run at

28
Q

Define phylogenetics

A

estimating relatedness between species based on sequence data

29
Q

How can we use molecular genetics to infer relatedness of species?

A

Looking directly at DNA sequences.

30
Q

Define speciation.

A

lineage-splitting event that produces 2 or more separate species.

31
Q

Give the biological species concept.

A

a group of organisms capable of interbreeding and producing fertile offspring.

32
Q

Define allopatric speciation.

A

speciation occurs in 2 populations of the same species that have become isolated from one another due to geographical changes.

33
Q

Define sympatric speciation.

A

speciation occurs in a single population.

34
Q

What is speciation reinforced by?

A 
-premating isolation:
Behavioural choices
Spatial constraints
Temporal isolation
Mechanical incompatibility

-post-zygotic isolation
Hybrid inviability
Hybrid sterility

35
Q

Give the ecological species concept.

A

a lineage with the same ‘adaptive zone’ or niche.

36
Q

Give the evolutionary species concept.

A

a single lineage of ancestor-descendant population which maintains its identity from other such lineages and which has its own evolutionary tendencies and historical fate.

37
Q

Define adaptation.

A

a change or the process of change by which an organism or species becomes better suited to its environment.

38
Q

If the rate of mutation or drift balances the selective pressure it may appear that…

A

the population is not under selection.

39
Q

Adaptation occurs when…

A

an organism displays traits that allow it to live in a particular environment and other factors permit this.

40
Q

What do biological factors limit?

A

The niche an organism can persist within.

41
Q

What promotes adaptation?

A
  • moderate mutation rates
  • a small amount of gene flow
  • directional selection
  • developmental competence (related to ancestry)
42
Q

What prevents adaptation?

A
  • inbreeding
  • genetic drift
  • large amounts of gene flow
  • stabilising selection
  • smaller populations have less potential for local adaptation than larger populations
43
Q

Any widespread population is likely to experience what in different parts of its range & the effect of this.

A
  • different environmental conditions

- it will soon consist of a number of sub-populations that differ slightly or even considerably.

44
Q

Define gradualism.

A

evolution generally occurs uniformly and by the steady and gradual transformation.

45
Q

Define punctuated equilibrium.

A

evolution is marked by isolated episodes of rapid speciation between long periods of little or no change.

46
Q

What was the Cambrian explosion?

A

sudden diversity of body plans.

47
Q

Define the use of homologous structures.

A

in extant species allow us to infer functions in related extinct species.

48
Q

Define the use of analogous structures.

A

in unrelated species where there is no common descent mean that great care must be taken in establishing functions of traits in extinct species.

49
Q

Give an example of how we can investigate the formation of complex structures.

A
  • eg the eye.

- we can look at different species of molluscs to look at all the stages of eye development.

50
Q

Define genetic hitchhiking.

A

traits may be selected for because they are linked to something

51
Q

Give an example of how evolutionary solutions are not optimal.

A

the mammalian eye have the choroid membrane in front of the retina which blocks the image.

52
Q

Give Dollo’s Law.

A
  • once a pathway of successive adaptations begins, reversal may be competitively disadvantageous or difficult to achieve.
  • ancestry apparently constrains the range of variation available to natural selection.
  • ie evolution is not reversible, structures or functions discarded during the course of evolution do not reappear in a given line of organisms.
53
Q

Give criticisms of the adaptationist agenda.

A
  • adaptationists seek to find adaptive explanation for every characteristic of an organism
  • however, some things do not have a purpose or role that relates to their function
  • some things are non-adaptive

BIO1334 Genetics (15 decks)

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