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General Biology I > lecture 21: evolution of populations and speciation > Flashcards

lecture 21: evolution of populations and speciation Flashcards

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1
Q

Fuel for evolution of populations?

A

Variation in traits based on genetic variation

Unit of evolution = population

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2
Q

What produces genetic variation in populations? (3)

A
  1. Mutations: permanent changes to DNA —> create new alleles (even new genes/genomes) in populations
  2. Sexual reproduction: creates different combinations of pre-existing alleles in populations
  3. Horizontal Gene Transfer (unicellular species): allows new alleles (or new genes) to be introduced into other populations
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3
Q

Describe importante of mutation in genetic variation and evolution

A
  • Introduce new alleles in populations
  • Mechanism of evolution, but is RARE (we have mechanisms to avoid mutations bc usually bad) —> so not an important force on its own
  • But, ultimate source of all genetic variation in population: if no mutations, no evolution
  • Primary source of genetic variation in asexual populations (bc lifetimes are shorter, so evolution happens faster)
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4
Q

Describe importance of sexual reproduction in genetic variation en evolution

A
  • Shuffle existing alleles into new combinations
  • NOT a mechanism of evolution, but a supporting factor
  • In organisms that reproduce sexually: shuffling of alleles = more important than mutation in producing genetic variation —> bc mutation is rare
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5
Q

How is evolution measured?

A

Measuring allele frequency changes in the gene pool

  • No change in allele frequency = No evolution
  • Small/large change in allele frequency = Evolution
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6
Q

What is “gene pool”?

A

All of the alleles of all the genes in a certain population

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7
Q

During evolution of populations, alleles can become… (2)

A
  1. Fixed: reach frequency of 1

2. Lost: frequency of 0

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8
Q

2 requirements of a population to be in genetic equilibrium

A
  1. Evolution is not occurring: allele frequencies are constant
  2. Mating is random: genotype frequencies are constant (no in breeding/choosing partner for specific phenotype)
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9
Q

How do you predict genotype frequencies in a population that is in genetic equilibrium?

A
  • Population-wide Punnett square
  • Assume: 1. no evolution and 2. mating is random
  • p = frequency of one allele
  • q = frequency of another allele
  • 1 = p^2 +2pq + q^2
  • Frequency of A1A1 genotype = p^2
  • Frequency of A1A2 genotype = 2pq
  • Frequency of A2A2 genotype = q^2
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10
Q

What is evolution?

A

A change in allele frequencies in the gene pool of a population

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11
Q

4 mechanisms of evolution in populations

A
  1. Natural selection
  2. Genetic drift
  3. Gene flow
  4. Mutation
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12
Q

Possible consequences of the four mechanisms of evolution in populations, Affect what? (2)

A
  • Each can change alleles frequencies and cause evolution in a pop.
  • Change will affect:
    1. Genetic variation (decrease, increase, maintain)
    2. Fitness of population (Decrease, increase)
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13
Q

What is natural selection and its consequences on genetic variation and fitness?

A
  • Mechanism: where certain alleles are FAVOURED
  • Effect on genetic variation: increases, maintains or decreases
  • Effect on average fitness: INCREASES FITNESS by producing adaptations
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14
Q

3 patterns of natural selection for quantitative characters

A
  1. Directional selection
  2. Stabilizing selection
  3. Disruptive selection

—> Quantitative, so frequency distribution of phenotypes = bell-shaped curve

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15
Q

What is directional selection?

A
  • Mechanism: favours one extreme and greatly reduces the other in the range of phenotypes (one extreme is high fitness and other is low fitness)
  • Consequence: results in directional change in the average phenotype —> trait/genetic variation in pop can be REDUCED
  • If directional selection continues: beneficial alleles —> fixed while harmful alleles —> lost via purifying selection
  • Usually limited by opposing directional selection form fitness trade-offs
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16
Q

What is stabilizing selection?

A
  • Mechanism: favours intermediate/medium phenotypes and reduces both extremes in populations (both extremes = low fitness and intermediate one = high fitness)
  • Consequence: NO change in average phenotype, trait/genetic variation is REDUCED
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17
Q

What is disruptive selection?

A
  • Mechanism: favours both extremes and reduces intermediate phenotype (both extremes = high fitness and intermediate one = low fitness)
  • Consequences: 2 average phenotypes develop over time (bimodal distribution), trait/genetic variation in pop is INCREASED
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18
Q

What is sexual selection?

A
  • Special case of natural selection where non-random mating causes evolution of pop
  • Favours individuals with heritable traits that ENHANCE FITNESS by increasing their change to attract mates
  • Usually a mechanism of evolution in males —> to compete for females
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19
Q

What is the fundamental asymmetry of sex?

A
  • Males and females have different roles in reproduction process
  • Roles produces DISTINCT criteria that increases fitness of a specific sex
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20
Q

What increases fitness in females?

A
  • Reproduction = energetically expensive in females
  • Strategy: reproduce a few times, but do it well
  • Need traits that allow her to:
    1. Support development of offspring
    2. Choose males with “good alleles” to pass on
    3. Choose male that will provide ressources and care for offspring
    —> These traits increase fitness in females
  • NOT sexual selection; this is natural selection
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21
Q

What increases fitness in males?

A
  • Reproduction = energetically cheap
  • Strategy = reproduce as often with as many females as possible
  • Lead to COMPETITION among males to attract males
  • Need traits that allow him to outcompete other males in attracting mates by:
    1. Force
    2. Being chosen by females
    —> These traits increase fitness in males
    THIS IS SEXUAL SELECTION, not natural
22
Q

2 types of sexual selection

A
  1. Female choice (intersexual selection): females choose males with “good alleles”
  2. Male-male competition (intrasexual selection): males compete for females
23
Q

Consequences of sexual selection?

A
  • Results in sexual dimorphism: traits differ between males and females
  • Males = usually many more traits that function in courtship/male-male competition as sexual selection is more intense in males
24
Q

What is genetic drift? Effect on genetic variation and fitness?

A
  • Mechanism: RANDOM increase/decrease in allele frequencies due to CHANCE EVENTS
  • Effect on genetic variation: tends to DECREASE genetic variation
  • Effect on average fitness: changes = RANDOM, so random effects to fitness; usually DECREASES fitness
25
Q

What causes genetic drift? (3)

A

Can occur by any process/event that involves SAMPLING ERROR where observed results do not fit expected results based on probabilities
1. Random fertilization
2. Population Bottleneck: accidents that remove individuals at random (natural disasters)
3. Founder event: small population can be separated from parent population
—> results in RANDOM changes in allele frequencies in pop. due to sampling error

26
Q

3 important points about genetic drift due to sampling in sexual reproduction

A
  1. Genetic drift changes are RANDOM with respect to fitness as they are caused by chance
  2. Over time: genetic drift can REDUCE genetic variation & cause harmful alleles to be fixed + beneficial ones to be lost OR contrary
  3. Effect of genetic drift = MORE pronounced in SMALL populations —> allele frequency change more rapidly as the smaller the population, the larger the sampling error
27
Q

What is gene flow? Effect on genetic variation + fitness?

A
  • Mechanism: addition/loss of alleles by movement of individuals in/our of population (immigration)
  • Effect on genetic variation: may increase or decrease
  • Effect on fitness: usually random, may increase or decrease
28
Q

Mechanisms in evolution of pop. usually reduce or increase genetic variation? Consequences?

A
  • Tend to reduce genetic variation
  • Pop. with reduced genetic variation = less chance to be able to adapt if there is a change in the environment —> risk of extinction
29
Q

What is mutation? Effect on genetic variation + fitness?

A
  • Mechanism: production of NEW ALLELES
  • Effect on genetic variation: INCREASE genetic variation —> RESTORES it
  • Effect on fitness: random with respect to fitness, may increase or decrease
30
Q

Consequences of mutations (small-scale) (3)

A
  1. Deleterious alleles: decrease fitness and can be eliminated by natural selection (purifying selection)
  2. Neutral alleles: no effect on fitness
  3. Beneficial alleles: rare, but increase fitness & favoured by natural selection
31
Q

Which type(s) of allele is (are) most commonly produced by mutation?

A

Deleterious (or neutral because of redundant codons)

32
Q

Would purifying selection occur faster if the deleterious allele was dominant or recessive in causing a life-threatening disease?

A

Dominant, because those who have it would most likely not be able to pass on alleles as they do not live long
If recessive —> can be carriers, so harder to purify

33
Q

Is mutation an important evolutionary mechanism?

A
  • No, bc it is rare —> mutation alone is slow compared with natural selection, genetic drift, and gene flow in eukaryotes
  • But combined with natural selection —> becomes important evolutionary mechanism
  • mutation = even more significant in bacteria + archaea —> short generation times = faster evolution
34
Q

What is speciation?

A

Splitting event that creates two or more distinct species from a single ancestral group —> if both are distinct enough, they start to diverge

35
Q

How are species identified (2)

A
  1. Biological species concept

2. Morphospecies concept

36
Q

What is the biological species concept + advantages & disadvantages?

A
  • Criterion: reproduction isolation —> no interbreed/fail to produce viable + fertile offsprings = distinct species —> reproductive isolation occurs when no interbreed so gene flow is cut off
  • Logic: no gene flow occurs between populations that are reproductively isolated from each other
  • Advantage: criterion is NOT subjective —> either they are reproductively isolated or not
  • Disadvantages:
    1. Can not be evaluated in fossils
    2. Or in species that reproduce asexually
    3. Difficult to apply when closely related population do not happen to overlap with each other geographically
37
Q

What is the morphological species concept + advantages & disadvantages?

A
  • Criterion: differences in size, shape, or other morphological features
  • Logic: distinguishing features = most likely to arise if pop. are independent and isolated from gene flow
  • Advantages: widely applicable (sexual/asexual species, fossils)
  • Disadvantages: can be very subjective
38
Q

Examples of PREzygotic reproductive isolation in the biological species concept

A
  • Reasons why they won’t attempt mating: habitat isolation (aquatic vs terrestrial), temporal isolation (day vs night), behavioral isolation (mating rituals:
  • Reasons why fertilization is not possible even if they attempt to mate: mechanical isolation (incompatible organs), gametic isolation (incompatible gametes)
39
Q

Examples of POSTzygotic reproductive isolation in the biological species concept

A
  1. Reduced hybrid viability: die young, not strong, unhealthy
  2. Reduced hybrid fertility: strong, but infertile
  3. Hybrid breakdown: usually in plants —> strong + fertile, but breaks down

—> Barriers that prevent production of viable and fertile offspring

40
Q

How does speciation occur?

A
  1. Isolation: pop. become reproductively (genetically) isolated
  2. Divergence: separate patterns of evolution (natural selection) cause population to diverge (start to have different traits)
41
Q

2 types of reproductive isolation

A

May occur in:

  1. Allopatry: GEOGRAPHICAL (physical barrier) isolation between pop. leads to reproductive isolation —> genetically isolated so undergo distinct evolutionary processes
  2. Sympatry: CONTACT members of populations possible but they become reproductively isolated —> possible gene flow, but does not happen
42
Q

How can geographical isolation happen? (2)

A
  1. Vicariance: physical barrier forms (mountain, river) to create sub-populations
  2. Dispersal: sub-population moves to another isolated habitat
43
Q

How can sympatric speciation happen? (3)

A
  1. Niche segregation: variation in niche & DISRUPTIVE selection where hybrids = LESS FIT
  2. Sexual selection: variation in mating preferences —> mating within sub-pop. = increases fitness
  3. Genomic changes: become genetically incompatible, common in plants
44
Q

How can genomic changes cause instant speciation?

A

Mistakes: chance events during cell division can create offspring in pop. with a POLYPLOID genome (more than 2 chromosomes per set)
—> Polyploid individual is reproductively isolated from parents species
—> Create offspring by self-fertilization —> Create pop. of new mutant species
- Common plants because self-fertilization

45
Q

How fast + how much changes occur for speciation?

A
  1. Can occur rapidly or slowly

2. Can result from changes in few or many genes

46
Q

2 models for speed of speciation

A
  1. Punctuated pattern: rapid bursts then long periods of no change (punctuated equilibrium)
  2. Gradual pattern: speciation gradually

—> Combination of both irl
- Punctuated equilibrium = explains why missing of many transitional forms in fossil record

47
Q

What are adaptive radiations?

A
  • Single lineage rapidly produces many descendant species
  • Opposite to mass extinctions
    1. Species forms monophyletic group
    2. Rapid speciation (burst)
    3. Ecologically diverse
48
Q

What triggers adaptive radiations?

A
  1. Ecological opportunity: availability or new resources and niches can drive adaptive radiations (niches become vacant after extinction of dinosaurs —> several species of mammals develop fast)
  2. Innovations: evolution of a key adaptation that allows individuals to exploit new resources and occupy different niches (ex: adaptations of flowers in angiosperms —> increases in effective mechanisms for reproduction on land)
49
Q

How do complex innovations develop?

A
  • Arise from modification of ancestral structures
  • But don’t need a complex innovation for it to be useful to its user
  • Result from exaptations (features that now have other functions that originally)
50
Q

What is Evo-Devo? Developmental biology?

A
  • Research at the interface between developmental biology and evolutionary biology
  • Development biology studies development process in organisms and the underlying cell and genetic mechanisms
  • Helps us understand:
    1. Evolutionary relationships through developmental homologies
    2. How major phenotypic change can occur during evolution
51
Q

What are Developmental control genes?

A
  • Not all genetic change is qual
  • Small genetic change to these control genes —> Can lead to LARGE phenotypic change (multiples changes
  • MASTER CONTROL GENES (homeotic genes) regulate expression of OTHER genes & direct developmental processes (pattern of body)
  • Genetic changes altering these genes —> Foundation of evolutionary change and speciation
  • Mutation can affect genre product itself OR its expression level OR expression pattern in time and space
52
Q

3 types of genetic changes +its consequences

A
  1. Genetic changes altering TIMING of gene expression —> affect TIMING of developmental events (when a gene is expressed: adult stuck in juvenile form) —> Heterochrony
  2. Genetic changes altering RATE of gene expression —>. affect RATE or developmental events (how long a gene is expressed) —> Allometric growth
  3. Genetic changes altering SPATIAL PATTERN or gene expression —> affect SPATIAL PATTERN of developmental events (where the genes are expressed)

General Biology I (19 decks)

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