Quiz 2 Flashcards
(161 cards)
1
Q
Systematics definition
A
The scientific study of the kinds and diversity of organisms and of all relationships among them
2
Q
Phylogenetics definition and fundamental assumption underlying phylogenetics?
A
Generating evolutionary trees
Assumption: Based on similarities we see between traits or organisms or between their sequences, how closely do we think they are?
3
Q
What two things contribute to differences between species (divergence between species from node)?
A
Genetic drift and natural selection
4
Q
True or false: all of the tips (extant taxa) on a phylogeny are equally evolved
- Explain why or why not
A
True
- All lineages on earth have had the same amount of time to “evolve”
- More changes = “more differentiated” but not “more evolved”
5
Q
Internal branch
A
Joins two nodes together
6
Q
External branch
A
Node to leaf
7
Q
Polytomy
A
How uncertainty is shown in a phylogeny
- don’t know which species are most closely related
8
Q
Monophyletic tree
- Also known as…
- And example
A
Part of a tree with an ancestor and all descendants (1 branch is cut; non-monophyletic - >1 branch is cut)
- aka clade
Ex: Vertebrata
9
Q
Paraphyletic tree
- Also known as…
- And example
A
Part of a tree with an ancestor, but not all descendants
- aka Grade
Ex: Birds with flight (excludes all the birds that lack flight)
10
Q
Polyphyletic tree
- And example
A
Part of a tree with where the group’s common ancestor is left out
- Ex: Organisms that have similar traits, but not because they have a common ancestor
11
Q
Homologous traits
A
Traits found in two or more species because of inheritance from common ancestor (common ancestor also had the trait)
12
Q
Analogous traits
A
Traits found in two or more species due to independent evolution (e.g. convergent evolution)
13
Q
What type of traits do we use to infer phylogenies? What would happen if we used the other type
A
We build phylogenies based on homologous traits. If we used the other type, we would infer that certain unrelated organisms are closely related based on phenotypes
14
Q
What are the three steps for generating a phylogenetic tree?
A
- Compile molecular and/or morphological data and align data
- Find the “best tree” using phylogenetic inference
- Estimate support for relationships (statistical test)
15
Q
The data used to infer phylogenies most typically is a compilation of which two things?
A
- Morphological characters
- Molecular data (DNA, RNA, amino acids)
16
Q
The evidence used to infer phylogenies must be analyzed to do what two things?
A
- Maximize homology: similarity that is the result of inheritance from a common ancestor
- Minimize homoplasy: similarity that is the result of convergence
17
Q
What are three features of phenotypic traits used for phylogenies?
A
- Almost always under some form of natural selection.
- Convergent evolution can result in homoplasies (cause errors for phylogeny)
- Easier to measure in fossils
18
Q
What are three features of using genome sequences for phylogenies?
A
- Rarely experience convergent evolution at sequence level
- Synonymous mutations are thought to be mostly neutral (so shouldn’t be evolving convergently)
- Difficult/impossible to measure in fossils
19
Q
What three traits have the slowest evolutionary rate? What type of evolution do they show?
A
- Codon-amino acid relationship
- Cellular house-keeping processes (e.g. histones)
- Basic body plan (e.g. 4 limbs in vertebrates)
These traits show purifying/stabilizing selection, as they are very conserved
20
Q
What trait has a “medium” evolutionary rate? What type of evolution does it show?
A
Synonymous mutations
- Neutrally evolving (a genetic trait or characteristic is changing over time due to random processes like genetic drift, not because of natural selection)
21
Q
What three traits have the fastest evolutionary rate? What type of evolution do they show?
A
- Immune system genes
- Body size
- Colouration
These traits are positively selected for
22
Q
Which traits are very poorly suited to evaluate traits that diverged a long time ago?
A
The traits with the fastest evolutionary rate, e.g. immune system genes, body size and colouration
23
Q
Define homology
A
Similarity that is the result of inheritance from a common ancestor
24
Q
When coding morphological characters, what are you generating?
A
A hypothesis of homology
25
What is an alignment?
When using molecular characters, you can use an algorithm to generate a hypothesis of homology, called an alignment
- Align DNA sequences to minimize the number of differences between them, by accounting for the fact that there can be indels, shifting the sequence
- A molecular alignment is a hypothesis of positional homology between bases/amino acids
26
Define parsimony
The simplest explanation that maximizes congruence and minimizes homoplasy (choosing the simplest explanation among alternative phylogenetic hypotheses
27
What are the 4 steps for parsimony analysis?
1. Choose an outgroup (a species that you have reason to believe is a distant relative of all the other species
2. Build all possible trees for the taxa
3. Map the data onto each tree to generate a "tree length" for every tree
4. Choose the "best tree" (i.e. the tree with the shortest tree length)
28
True or false: the likelihood of a base pair mutating from one to another and back again are not equal
- Explain why or why not
True; transitions are more common than transversions. Therefore, some genetic changes are much more likely than others when building phylogenies
- To account for transitions/transversions, a model would be similar to the molecular clock model, but incorporate different kinds of mutations (there are all sorts of different factors that we need to take into account, such as relative base frequencies, back substitutions, synonymous/non-synonymous substitution ratios, transition/transverstion ratio, number of substitutions per site, different rates in different parts of the molecule, etc)
- So the simplest explanations are not always the best because if you were to use parsimony, you would miss these
29
Explain how codon bias relates to natural selection
Organisms prefer certain tRNAs, making it more efficient to use specific codons over others. Natural selection favours these efficient codons because they increase translation speed and accuracy.
30
The greater the number on a node representing jacknife support values, the...
Higher the confidence that that node is correct (the higher the number, the stronger the support)
31
As branch length increases, what happens to confidence values for each node?
They increase (if two species are more recently diverged, there's less information available to make phylogeny support
32
How does migration affect diverged populations? What happens as migration rate increases/decreases?
Migration pulls these populations back together
As migration rate decreases, populations diverge more and vice versa
33
How does genetic drift affect diverged populations?
Genetic drift causes fading between populations
34
Define inbreeding
Mating between relatives (a form of assortive mating, which is non-random mating: some kind of rule by which you're mating)
35
How does inbreeding impact homozygote and heterozygote frequencies
Homozygotes fix, but heterozygotes are lost
- closely related individuals are more likely to share identical alleles
- Each lineage is acting like a mini population
36
What is the ultimate form of inbreeding?
Selfing (breeding with yourself; seen in hermaphrodites)
37
Inbreeding in large populations occurs almost exclusively because of...
Non-random mating
38
Why is the probability of inbreeding increased in organisms with limited dispersal?
Happens because in organisms with limited dispersal, neighbouring individuals tend to be related
- Inbreeding happens by chance here, because you just happen to bump into your cousin and mate
39
How is inbreeding measured?
By the inbreeding coefficient, F
40
What is F (the Fixation Index)?
The probability that an individual's two alleles at a particular locus are derived from the same copy of the allele in a previous ancestor
41
When are alleles said to be "identical by descent" (IBD)?
When two alleles at a particular locus are derived from the same copy of the allele in a previous ancestor
42
The deficiency of ______ estimates the extent of inbreeding in a population
Heterozygotes
43
What is the formula for the F coefficient?
F= (HE-H)/HE
HE: Expected proportion of heterozygotes in a large, randomly mating population (HE=2pq)
H: Observed proportion of heterozygotes in a population
44
How to calculate HE for formula F=(HE-H)/HE
HE=2pq
45
What are the values for HE, H and F in the absence of inbreeding?
HE=H, so F=0
46
What are the values of HE, H and F given complete inbreeding?
H=0, so F=1
47
When will H be greater than HE? How does this affect F?
In some cases (e.g. hybridization), H>HE, so F<0
48
What is the value of F at Hardy-Weinberg equilibrium?
F=0 because H=HE
49
If you observe a domesticated population with a high amount of inbreeding (F=0.5) due to previous breeding practices, how long would it take for the population to go back to approximately F=0 if you allowed all of the individuals to randomly mate (ignore deviations due to population size)?
1 generation
- HWE re-establishes with 1 generation of random mating (assuming all the other assumptions are also met), and at HWE, F=0
50
Why does inbreeding lead to increased incidence of disease?
Mutations that happen in humans are usually recessive, so increased frequency of homozygosity due to inbreeding results in more recessive homozygotes
51
How would the F coefficient change in a family experiencing inbreeding throughout a long period of time?
It would increase each generation
52
Describe inbreeding depression
Reduced fitness due to inbreeding, so highly inbred lineages experience higher infant mortality per generation
53
How do genetic bottlenecks often go hand in hand with inbreeding and selection
Having a bottleneck increases inbreeding later on, and bottlenecks also decrease genetic variation for selection to act upon
54
What do estimates of Ne take into account?
Deviations from idealized conditions (i.e. inbreeding)
55
How do populations act relative to each other in terms of allele fixation when migration is high?
They act as one "big population", and all go in the same direction
56
How do populations act relative to each other in terms of allele fixation when migration is low?
They go in different directions when migration is low.
57
How to calculate HT?
Expected number of heterozygotes for an entire population:
HT=2pTqT
58
How to calculate HS (HS,i) for each separate population?
2piqi
59
How to calculate average expected heterozygosity across demes? HS bar
HS bar = (sum of Hs,i)/d
60
What does FST measure and what is the formula?
FST measures the divergence in allele frequencies among subpopulations by contrasting the expected heterozygosity in the subpopulations
- FST is the scaled difference between the overall expected heterozygosity (HT) and the expected heterozygosity within populations (HS)
FST= (HT-HS bar)/HT
61
What does it mean when FST=0?
The two sub-populations (demes) have similar allele frequencies
62
What does it mean when FST=1?
The two sub-populations (demes) are maximally different (have opposite allele frequencies)
63
The greater the FST, the (higher/lower) the divergence in allele frequency between populations
Higher
64
When FST >>0, there are (more/less) heterozygotes than expected for the whole population
less
65
What is the Wahlund effect?
When heterozygosity is low because of previously undetected population structure (It occurs when individuals from genetically different subpopulations are combined into a single sample; when a population is made up of smaller separate groups that don't mix much)
66
What are four ecological factors (in general) that might cause the different amounts of divergence between two demes?
1. POPULATION SIZE (i.e. small populations have greater allele fluctuations)
2. MIGRATION (i.e. populations diverge from one another when they have low migration rates)
3. Mutation (new alleles)
4. Drift (random changes in alleles)
67
True or false: gene flow/migration counteracts the effects of genetic drift
True; gene flow increases the genetic similarity among populations
68
What thing(s) could cause two demes to have the same allele frequencies (FST=0, all the variation is within populations)?
High migration rates OR short/no time of isolation(very short amount of time that they've been drifting
69
What thing(s) could cause two demes to be maximally different in allele frequencies (FST=1, all variation is between populations)?
No migration AND long time of isolation
70
In what two ways can gene flow occur?
1. The individuals themselves can move between populations between breeding
2. Adults may remain in original population but gametes are distributed widely
71
True or false: gene flow changes the allele frequencies of the whole species
False; gene flow does not change allele frequencies of the whole species, but may change the local allele frequencies when migrants are different from residents (leading to a change in the FST)
- Gene flow is just moving alleles from one place to another (no individual is living or dying, stuff is just shifting around)
72
If you have a population with many sub-populations, each with one allele present, what would the relative HS and HT values be?
HS=0 but HT would be high (because 2pTqT)
- so you would have a pretty big difference between HT and HS
73
The smaller the population size, the (lower/higher) the migration needs to be to counteract genetic drift (to keep populations together)
Higher
74
Which of these statements about FST would be correct in the simulations we ran in class?
a) It would be lower or equal at the beginning of the simulations than the end
b) It would be lower when migration is lower
c) It would be lower when population size is lower
d) A+B
e) A+C
f) B+C
g) A+B+C
A
All the populations start at the same allele frequencies -> no divergence to begin with
- If migration is high, then FST would be low at the end of the simulations as well
Not B: Low migration, populations aren't mixing, high FST
Not C: When pop. size is low -> populations drift apart, high FST
75
If you see high FST, what 3 things could be causing this?
1. Low migration between populations
2. High genetic drift
3. Populations have been diverged for a while
76
How does gene flow affect allele frequencies among populations?
Homogenizes allele frequencies
77
Describe the interplay between genetic drift and gene flow
Allele frequencies in subpopulations diverge because of genetic drift (increases FST), gene flow between subpopulations counteracts the differentiation caused by genetic drift (decreases FST), and given sufficient time, homogenizing effects of gene flow should balance diversifying effects of genetic drift reaching an equilibrium (the rate of divergence between populations = the rate of coming together)
78
What did Sewall Wright show?
Showed that if subpopulations exchange a fraction, m, of individuals each generation and m is small, then for neutral genes:
FST(equilibrium)= 1/(4Nem+1)
79
What does Nem represent?
The number of migrants each generation
80
At what relative Nem values do populations start to diverge?
Nem<1
81
True or false: Even limited gene flow greatly counteracts the divergence of allele frequencies among populations as a result of genetic drift
True
82
What does an Nem value of 0.25 mean?
1 migrant every 4 generations
83
Wright's solution for FST assumes what type of population?
An idealized population, called the island model
84
What are the 5 assumptions of the island model?
1. Equal and symmetrical migration among all demes
2. Equal and unchanging deme size
3. No extirpation (when a population goes extinct)/recolonization
4. No selection
5. Very low mutation (µ<
85
Describe the wolf example, showing the strong impact of even a single immigrant in a population
Wolves had gone extinct in the Scandinavian peninsula (Sweden and Noway) by the 1960's (from poisoning and hunting)
Based on microsatellite DNA, this pack was descended from a single founding pair which had migrated from Finland and Russia
During the 1980's, genetic diversity (heterozygosity) in this pack declined steadily as a result of inbreeding
In association with the decline in heterozygosity, the pack population size remained small
This limitation of population size probably reflects the consequences of inbreeding depression
In 1991, a migrant male entered the population, bringing with him alleles that were not in the existing population.
Introduction of these novel alleles into the population immediately increased the heterozygosity in the "new" animals that appeared
F=-0.08 for animals born after 1996, which was significantly less than 0
- Observed heterozygosity exceeded that expected by random mating (inbreeding avoidance)
- Population grew exponentially, showing a strong impact from a single immigrant in the population
86
What happened to the heterozygote frequency (genetic diversity) as humans expanded out of Africa?
Decreased, due to founder effects (bottlenecks)
87
True or false: genetic structure reflects geography
True
- e.g. individuals from Spain and Portugal all look similar to each other, they look a little bit more similar to France than they do to Switzerland or Austria
88
When looking at a Manhattan plot of the FST for different alleles, why would there be multiple points showing FST instead of just a single one?
Due to linkage disequilibrium (neutral SNPs hitchhike)
89
What does it mean if we have a negative FST?
HS>HT, due to statistical error (not the same thing as increased heterozygosity due to inbreeding)
90
What might be happening if two sub-populations have the exact same allele frequency of an allele over time?
Migration rate is very high (e.g. m=0.5), so they are effectively a single population
91
What might be happening if allele frequencies are obtained over time for two different species colonizing small islands from the mainland, if species 1 shows increased divergence (high FST) and species 2 shows a small amount of divergence (low FST)?
They have similar rates of gene flow connecting the populations but species 1 has a smaller population size
OR
They have similar population sizes, but species 2 is experiencing more migration between all three populations
92
What could you say about the allele frequencies if they increase very very slightly in two different sub-populations?
The population is probably very large in both species (smallest change in allele frequency)
93
What could you say about 3 alleles (A, B and C) if they're all sampled from a single population but B and C look like they fluctuate together, whereas A fluctuates the opposite direction?
Higher LD between alleles B and C (close together in the genome)
94
Define Mendelian genetics
Controlled by a single genetic variant (e.g. sickle cell anemia, lactose digestion)
95
Define oligogenic genetics
Influenced by a few genes of large effect (e.g. coat colour in mice)
96
Define polygenic genetics
Influenced by many genetic loci (e.g. body size, drought tolerance)
97
True or false: quantitative traits vary continuously
True
98
Mendelian geneticists pointed to traits with a simple genetic basis, showing _____ variation. Biometricians pointed to _____
Discrete
The resemblance between relatives in continuous traits
99
Is the variation responsible for evolution continuous or discrete?
Both
100
Who resolved the controversy of the question "Is the variation responsible for evolution continuous or discrete?" and how?
Fisher resolved this controversy showing how the segregation of Mendelian genes could give rise to continuously distributed phenotypes
- This was the founding of population genetics
101
What happens as the number of loci increases for polygenic traits?
You move towards a normal distribution (the number of possible genotypes increases, the effects of loci are additive and the number of phenotypes increases)
102
What happens to the distribution of genotypes across loci as you add environmental variation?
Traits look more continuous in nature
103
What did Fisher show in terms of allele frequencies?
He showed how the allele frequencies could be related to the mean and variance of the genotype distribution.
- You could relate the underlying genetic variation to how your normal distribution looked in terms of where it was in its mean and variance.
- This is important because it allowed us to study genetics by just doing statistical measurements, looking at means and looking at variances, without knowing anything about the underlying alleles (often we don't know which genes control a trait, but we can measure its mean and variance)
104
Define plasticity
A single genotype produces different phenotypes depending on the environment
105
Define genotype x environment interaction (GxE)
A special kind of plasticity, with a trade-off between genotype and environment (e.g. genotype 1 biomass increases at high light and decreases in low light, while genotype 2 biomass follows the opposite pattern. So it's not like more light is good for every genotype, there's tradeoffs)
106
What's an example of a non-tradeoff effect of plasticity?
How most plants will grow better with more nitrogen
107
Describe the top-down approach of evolution
Quantitative genetics studies how variation in heritable phenotypes is related to fitness (following the changes in mean phenotype caused by selection, without worrying about which genes are involved)
108
Describe the bottom-up approach of evolution
Population genetics studies how allelic variation affects traits/fitness
109
What formula describes Vp (phenotypic variation)?
Vp=VG+VE+VGxE
- VG(genetic variance): The component of phenotypic variance governed solely by the genetic effects, regardless of the environment
-VE: The component determined solely by environmental effects, regardless of genotype (pure phenotypic plasticity, has no impact on allele frequencies
- VGxE: Represents the component of phenotypic variance arising when genetic effects depend on the environment in which they are expressed
110
What can genetic variance (VG) be further decomposed into?
VG=VA+VD+VI
- VA= additive genetic variance, due to the allelic variation itself
VG=~VA
111
What formula describes VA (additive genetic variance due to allelic variation itself)?
VA=2pqa^2
112
a values in 2pqa^2for homozygotes and heterozygotes
homozygotes: -a/+a
heterozygotes: 0
113
When 99% of all individuals have allele A1, there is (a lot/very little) variation in the population and variance (VA) is (high/low)
Very little, low
114
When 50% of all individuals have allele A1 and the other 50% have allele A2, there is (a lot/very little) variation in the population, and variance (VA) is (high/low)
A lot (maximized), high (maximized)
115
If x loci contribute to trait variation, then VA is the...
Sum across the VAs across all loci
116
The greater the number of loci that are affecting a given trait, the (lesser/greater) the VA for that trait
Greater
117
If everything else were equal between these scenarios, which one would you expect would have the highest value of VA if the trait being studied were purely neutral (no fitness effect)?
a) Ne=100, µ=10^-8
b) Ne=100, µ=10^-7
c) Ne=100000, µ=10^-7
d) Ne=10000, µ=10^-8
C
π=4Neµ, so the example with the highest combined values of Ne and µ would have the highest nucleotide diversity, and all else being equal, should mean more trait variation
- Higher diversity = higher pq = higher variance because greater number of loci at higher frequencies
118
Describe how effective population size impacts VA
VA is higher in larger populations - but it plateaus, due to effect of selection
- Drift limits variance in smaller populations (at small Ne)
119
Define narrow sense heritability and provide its formula
The proportion of variance that can be passed on to the next generation (the proportion of variance that is due to genes)
h^2=VA/VP
VA: contribution from genes
VP: contribution from genes and environment
- No units (it's a proportion), so h^2 can be compared easily among species and traits
120
True or false: h^2 may be very sensitive to conditions of an experiment
- Explain why or why not
Because it depends on VE, it may be very sensitive to conditions of the experiment
121
Other than using the formula, what's another way we can estimate heritability?
Using the slope of the regression of offspring on mid-parent trait values
heritability (h^2)=b(parents-offspring)
122
How can heritability be estimated in experimental procedures?
Heritability can be estimated by a number of different experimental procedures comparing the resemblance among relatives.
123
What is a fundamental limit of heritability estimates?
The fact that progeny may resemble parents for other reasons (i.e. environmental, and not genetic, reasons)
SIMILARITY IN ENVIRONMENTS BETWEEN PARENTS AND OFFSPRING CAN RESULT IN BIAS
124
What are two ways that progeny may resemble parents for reasons other than genetics?
1. Parents and progeny live in the same environment (e.g. natal breeding sites of salmon and birds)
2. The condition of parents can influence phenotype of progeny (e.g. food availability is low in parents, conditions of parents is therefore low and thus condition of progeny born will be low irrespective of the genotype
125
Heritability is a function of the (individual/population)
- Explain
Population
Determined by environmental variances, thus strictly a property of a particular population. Different populations can have different heritabilities
126
True or false: A heritability value of 0 for a trait indicates that the given trait is not heritable
- Provide a example
False; if there is no genetic variation in a population, the heritability if the trait will be 0, even if the trait itself has a genetic basis
e.g. an inbred line may show features that are the result of genetic differences relative to other lines (actual heritable differences). However, since there is no variation within this hypothetical inbred population, h^2=0.
127
Explain the heart/stomach example for estimating variance
Having a heart and stomach is genetically determined, but since everyone has them (no variation), their heritability is 0.
- So heritability is not the same thing as something being genetically determined
128
If F=0, is the population at HWE?
Not necessarily, as the homozygotes could be out of the proportions, but still have the heterozygotes be = 2pq
129
What are 3 ways in which natural selection is different from other evolutionary processes?
1. The outcome is predictable from one generation to the next
2. The action of natural selection depends on the phenotype
3. Only natural selection results in adaptation, which is the goodness-of-fit between an organism and its environment
130
True or false: Fisher showed population genetics and quantitative genetics approaches to studying selection to be completely equivalent
True
131
What is Breeder's equation and what relationship does this show between the response to directional selection and heritability?
R=h^2S (for directional selection only)
- Shows that the response to directional selection varies directly with heritability
132
Formula for selection differential
S=µs-µ (the difference between the mean phenotypes of the parents after selection, µs, and the entire population before selection, µ)
133
True or false: R=h^2S is only used for stabilizing selection
False; it's only used for directional selection
134
What is µ'?
The mean phenotypes of the offspring generation
135
What is the formula for response to selection (not using heritability)?
R=µ'-µ
136
Explain how the response to selection is proportional to VA/VP, which is h^2
Only the effect of selection on the genetic component of variation (VA) is passed on to the next generation. The effect of selection on environmental component of phenotypic variation (VE) is lost because it's not heritable
137
What does the selection differential measure in general?
S measures the strength of selection
- Bigger S = stronger selection = smaller number of individuals survive/reproduce
138
What happens to the response to selection if h^2 =0? Explain why
If h^2=0 then R=0
- If heritability is 0, then any changes in allele frequencies caused by selection would not be passed on
139
What happens to the response to selection if h^2 =1? Explain why
If h^2=1, then R=S
- If heritability is 1, then any changes in allele frequencies caused by selection would be passed on
140
Higher heritability results in (smaller/larger) response to selection (R)
Larger
141
What is Fisher's fundamental theorem of natural selection?
The rate of increase in fitness of any organism at any time is equal to its genetic variance in fitness at that time
- If you could measure the heritability of fitness exactly, then R would be the change in fitness from one generation to the next (R=h^2S)
142
Natural selection occurs when there is an association between which two things?
A phenotype and fitness
143
Difference between selection differential and selection gradient
Selection differential is the difference between the mean of selected and non-selected individuals, while the selection gradient is the slope of the regression between fitness and phenotype
144
True or false: neutral alleles are easy to detect within a population
False; it's hard to prove that an allele is neutral, maybe we don't have the statistical power to detect it.
145
If there is a flat relationship between body size and fitness, what would you predict would happen to the species body size over time? Select all that apply
a) Body size would not change over time in an infinite population
b) Body size would gradually increase
c) Body size would gradually decrease
d) Body size would change randomly, faster in a small population
e) Body size would change randomly, faster in a large population
A and D
146
Describe the change in the trait mean and the selection gradient in directional selection
Evolution of the trait mean (at least)
- Occurs when fitness varies positively or negatively with trait size
- Directional selection occurs when the linear selection gradient (slope) is significantly different from 0
147
Describe the change in the trait mean and the selection gradient in stabilizing selection
When the selection gradient is quadratic and negative (γ<0), selection is stabilizing
- Variance decreases between generations, but the trait mean does not change
148
What would happen to heritability if stabilizing selection continued for many generations?
The trait variance would be reduced to 0, so the phenotypic variation condition for natural selection would no longer hold and selection would stop
- Vp decreases, h^2 approaches 0
149
True or false: Most organisms are probably under stabilizing selection most of the time
True
150
Describe the change in the trait mean and the selection gradient in disruptive selection
When the selection gradient is quadratic and positive (γ>0)
- Phenotypic variance increases between generations, can cause divergence if there is something else that prevents interbreeding (some type of assortative mating)
- Average individuals have lower fitness than extreme individuals
- Trait mean does not change
151
True or false: for disruptive and stabilizing selection, one generation of selection is enough to change the variance
True
152
True or false: In directional selection, one generation of selection causes a change in trait mean that is proportional to heritability
True
153
True or false: A given population experiencing directional selection cannot be experiencing disruptive or stabilizing selection at the same time
False; a given population may be experiencing both directional selection and either disruptive or stabilizing selection
154
True or false: stabilizing selection dominates in populations
False; studies have shown that disruptive selection is about as common as stabilizing selection
155
Describe adaptive fitness landscapes
Coined by Sewall Wright
The X and Y axes represent trait values, while the Z axis represents fitness.
Evolution by natural selection favours more fit individuals, so populations always climb upwards on the landscape, until they find a local optimum
156
What kind of selection would a population be experiencing if it was climbing a peak on an adaptive landscape?
Directional selection
157
What kind of selection would a population be experiencing if it was climbing up multiple peaks in an adaptive landscape?
Disruptive selection
158
True or false: evolution by natural selection is an INEVITABLE consequence of three conditions: variance, inheritance and differential reproductive success in association with that variation
True
159
If pairwise FST values between sub-populations are not equal, what does this say about Wright's island model?
It says that these populations aren't following Wright's island model assumptions
160
What model that we looked at requires an equilibrium between genetic drift and migration?
Wright's island model
161
Wright's island model assumes that the alleles are...
Neutral
