HURST Flashcards
(128 cards)
1
Q
what year was on the origin of species published?
A
1859
2
Q
what were the 2 main ideas presented by origin?
A
the continuity of species + evolution by natural selection
3
Q
who else had similar ideas to darwin before him?
A
James Hutton and Patrick Matthew
4
Q
What age did lord kelvin estimate for the earth and why?
A
20-40 million years based on heat loss from a molten origin
5
Q
Why was kelvin’s estimate for the earth’s age inaccurate?
A
Because he didn’t account for radioactive heat and mantle convection
6
Q
what is fisher’s fundamental theorem of natural selection?
A
the rate of evolution = additive genetic variance in relative fitness
7
Q
what does high additive genetic variance in fitness imply?
A
faster adaptive evolution due to more heritable variation in reproductive success
8
Q
what does haldane’s work allow us to calculate?
A
the selection coefficient (s) from observed allele frequency changes
9
Q
what does the selection coefficient measure?
A
the strength of selection on a trait
10
Q
Give me some examples of rapide evolution occurring
A
HIV, penicillin and Cod
11
Q
Why do modern cod mature earlier and stay smaller?
A
selection from fishing pressures for larger, older fish
12
Q
what does recent evidence suggest about the speed of evolution?
A
evolution can occur rapidly - the puzzle is why long periods show little change?
13
Q
if the selection coefficient is 0 what does that mean for the allele?
A
it is fit and there is no selection against it
14
Q
if the selection coefficient is larger than 0 what does that mean for the allele?
A
there is selection against it
15
Q
why does natural selection require heritable traits?
A
because otherwise, selection has no lasting effect - traits must be passed on to affect evolution
16
Q
what is blending inheritance?
A
a now discredited theory where offspring traits are the average of their parent’s which reduces variation
17
Q
why does blending inheritance undermine natural selection?
A
it eliminates variation, leaving no fittest individuals for selection to act upon
18
Q
how does mendelian inheritance resolve blending inheritance?
A
it preserves variation through discrete alleles across generations
19
Q
what are discontinuous traits?
A
traits that are contolled by one gene and fall into distinct categories
20
Q
what are the hardy-weinberg assumptions
A
random mating, no mutation, no selection, no gene flow and infinites population size
21
Q
define allele frequencies p + q
A
A=p, a=q (p+q=1)
22
Q
define genotype frequencies
A
AA=p2, Aa=2pq, aa=q2
23
Q
what happens to variation under mendelian inheritance without selection
A
variation is maintained and genotype freqs stay stable
24
Q
what is meant by fitness in evo terms?
A
relative reproductive success of an allele
25
what is the equation for allele frequency with selection?
p' = [p²(1+s) + 2pq(1+hs)/2] ÷ W
Where W = mean fitness of the population.
26
what does 'h' represent in selection models?
it refers to the dominance of the beneficial allele (h=1 means fully dominant)
27
what would it take for a rare allele to spread?
the fitness of the heterozygote must be greater than the homozygote for the common allele
28
does the mode of inheritance affect whether a new allele spreads under selection?
no - if the heterozygote has higher fitness, the allele increases regardless of the mode of inheritance
29
what does it mean for an allele to invade?
it increases in freq from a low freq due to selection
30
What question helps determine if an allele can invade?
Will the allele's frequency increase when rare? (Check if slope > 1 when p is near zero.)
31
can alleles invade when rare?
yes, if it provides a fitness advantage
32
what are the 3 levels at which evolution can be considered?
species (group selection), individual, allele (gene selection)
33
what does group selection predict for sex ratios?
female biased sex ratios to maximise reproduction (since males only provide sperm)
34
what does fisher's sex ratio theory say?
1:1 sex ratio is more evolutionarily stable, if one sex is rare, alleles producing more of it will be favoured
35
what is a panmitic population?
A panmictic population is one in which all individuals mate randomly with no restrictions, forming a single, genetically mixed group
36
what does hamilton's local mate competition predict?
sex ratios become female-biased if males compete with brothers (wasps in caterpillars)
37
why are sisters more related in haploid-diploid species like bees?
sisters share 75% of genes (from haploid father and 50% from diploid mother) - makes sister-sister cooperation favourable
38
what happens if inheritance isn't mendelian?
alleles can spread even if harmful to individuals if they are transmitted more than 50% of the time (k>0.5)
39
what does k=0.5 mean?
inheritance isn't mendelian
40
what is meiotic drive?
a process where certain alleles distort meiosis to be passed on more than 50% of the time
41
why is meiotic drive considered a selfish genetic element?
It spreads despite reducing individual fertility or harming organismal fitness
42
give examples of selfish genetic elements
male-killing cytoplasmic elemtns (ladybirds), X-linked meiotic drive (flies)
43
how does natural selection differ from gene selection?
natural selection often focuses on phenotype, gene selection focuses on whether a gene increases its own frequency
44
What does it mean if p(AB) ≠ p(A) × p(B)?
It means alleles A and B are not inherited independently, indicating linkage disequilibrium (D ≠ 0)
45
what is linkage disequilibrium?
a non-random association between alleles at different loci measured by: D = p(AB) - p(A)p(B)
46
what causes linkage disequilibrium initially?
when a new, rare mutation arises on a haplotype which creates a non-random association
47
what is the formula for LD decay over generations?
Dₙ = (1 - r)ⁿ × D₀, where r is the recombination rate
48
what happens to D when r=0 (no recombination)?
D remains constant so LD persists
49
what happens to D when r=0.5 (unlinked loci)?
LD decays quickly as loci begin to behave independently
50
how does LD help locate disease-causing genes?
SNPs in strong LD with a disease allele indicate proximity to the disease causing locus
51
why does selection favour lower mutation rates in sexual species?
most mutations are deleterious and if unlinked, mutator alleles can't benefit from the spread of advantageous mutations they produce
52
when can a mutator allele spread in a population?
if it's tightly linked to a beneficial mutation it caused, it can hitchhike with the mutation
53
what is genetic hitchhiking?
when an allele rises in frequency due to linkage with a beneficial allele under selection
54
what genomic pattern does hitchhiking produce?
a region of reduced variation (low polymorphism) around the selected locus
55
where is human genetic diversity highest and lowest?
highest at chromosome tips and lowest in centromeres (recombination rates)
56
what is PS-QR=D used for?
to calculate LD from gamete frequencies
57
what happens to diversity immediately after selection?
it drops sharply near the selected allele due to hitchhiking
58
what is a mendelian trait?
a trait controlled by a single gene (discrete/discontinuous variation)
59
what is a quantitative trait?
a trait influenced by many genes and environment (continuous variation)
60
what does VP= VG+VE mean
Phenotypic variance (VP) equals genetic variance (VG) plus environmental variance (VE)
61
what is heritability?
proportion of phenotypic variance that is due to genetic variance
62
what is broad sense heritability?
H² = VG / VP
It includes all genetic effects: additive, dominance, and epistatic variance
63
what is narrow sense heritability?
h² = VA / VP
It includes only additive genetic variance (VA) — the part passed from parent to offspring
64
what does a high narrow=sense heritability mean?
offspring are more likely to resemble parents as the trait's variation is largely determined by the effects of additive alleles than environmental factors
65
Why is narrow-sense heritability important for selection?
Because only VA predicts a trait’s response to selection — it determines how much offspring resemble parents.
66
what are the components of genetic variation
additive variance, dominance variance and epistatic variance
67
What does it mean if H² or h² = 0?
no genetic contribution to variation in the population, doesn't undermine the importance of genes though
68
how can heritability be measured?
parent-offspring regression
inbred line comparisons
concordance rates
selection experiments
69
how does parent-offspring regression estimate h²?
the slope of the regression line of offspring vs mid-parent trait values estimates narrow-sense heritability
70
limitations of hat are limitations of parent-offspring regression?
they might both share an environment which could confuse the genetic input
71
what does the parent-offspring regression measure?
how much offspring resemble their parents for a particular trait
72
what are problems in twin studies of heritability?
identical treatment of monozygotic twins, shared environment can mimic genetic effects
73
what is a selection experiment?
Applying artificial selection to a trait over generations to see if it responds — indicating heritability
74
what is the response to selection equation?
Response = h² × Selection differential
This predicts the amount a trait will change per generation
75
what is fluctuating asymmetry? does it show heritability?
random differences between left/right traits - rarely heritable
76
why can't farmers breed animals with skewed sex ratios?
there is no heritable genetic variation in sex ratio - it is under strong evolutionary constraint
77
give me two examples of traits rarely showing heritability
fluctuating asymmetries + genetic limits (sex ratios)
78
what does high heritability mean for evolution?
the trait is likely to respond to selection - contributes to evolutionary change
79
what do traits with no heritable variation suggest?
they may be under evolutionary constraint
80
what does the modern synthesis propose about the primary driver of evolution?
natural selection acts upon genetic variation
81
what are 2 key assumptions of the mdoern synthesis
polymorphisms are rare and only most advantageous alleles persist + evolution occurs at a slow pace because of mutation selection
82
what is the gene-centered view of evolution?
evolution is seen as changes in allele frequencies within a population
83
what did gel electrophoresis reveal about the modern synthesis?
it highlighted that polymorphism wasn't rare as there was high protein diversity
84
what implication did lewontin's study have on the modern synthesis?
it showed that natural selection couldn't fully explain genetic diversity - genetic drift may play a role
85
what did kimura observe about the rate of molecular evolution that contradicted haldanes prediction?
1 substitution every 2 years - much faster rate
86
what is the core idea of the neutral theory?
most molecular mutations are neutral and evolve via genetic drift and not selection
87
how is the fixation probability of a neutral allele created?
1/2N, where N is the population size
88
what is the formula for the rate of neutral evolution?
Rate = p(fixation) × mutation rate = 1/(2N) × 2Nμ = μ.
89
what does the neutral theory predict about the rate of evolution across species?
it should be constant if all species have the same generation time
90
what are 2 possible out comes of drift?
fixation or loss of alleles
91
what does the nearly neutral theory add to the neutral theory?
it includes mutations with slight fitness effects
92
what happens to weakly deleterious mutations in small vs large pops?
small: can drift to fixation
large: eliminated by selection
93
how does pop size affect the efficiency of selection?
large: more efficient selection
small: stronger genetic drift, less efficient selection
94
what kind of mutations are likely to fix in small populations?
neutral and weakly deleterious mutations
95
What is the fixation rate of strictly neutral mutations?
Equal to the mutation rate (μ)
96
how are efficiently neutral mutations defined?
Mutations with |s| < 1/(2Ne); behave like neutral mutations, especially in small populations
97
why do small populations tend to have more junk DNA?
genetic drift weakens selection against non-functional DNA
98
what are the 3 major theories of molecular evolutionary change?
positive selection
strict neutral evolution
nearly-neutral evolution
99
what is the Ka/Ks ratio?
the ratio of non-synonymous (Ka) to synonymous (Ks) substitution rates in protein-coding genes
100
how is the Ka/Ks ratio interpreted?
Ka/Ks = 1: Neutral evolution
Ka/Ks > 1: Positive selection (advantageous mutations are being fixed)
Ka/Ks < 1: Purifying (negative) selection (deleterious mutations are being removed)
101
what is a synonymous substitution?
a nucleotide that doesn't change the amino acid sequence of the protein
102
how do you calculate Ka and Ks?
Ka = Ln / Nn
Ks = Ls / Ns
Where:
Ln = # of non-synonymous substitutions
Ls = # of synonymous substitutions
Nn = # of non-synonymous sites
Ns = # of synonymous sites
103
what is the dispersion index?
tells us whether substitutions happen randomly (Poisson process) or show signs of non-random forces, like selection or rate variation
104
what statistical distribution does neutral theory predict substitutions will follow?
a poisson distribution where mean=variance
105
what does it mean when D>1 in real data
there is more variation than expected under neutrality -> possible selection of episodic evolution
106
what is episodic evolution?
periods of rapid evolutionary change in specific lineages or genes due to bursts of selection
107
how do population bottlenecks affect evolution?
they increase drift which allows slight deleterious mutations to fix -> faster evolution in smaller populations
108
why is protein evolution faster in some lineages?
positive selection in specific lineages
bottlenecks reducing selection efficiency - nearly neutral theory
109
What are branch and site tests
Site tests: Look for specific codons under positive selection
Branch tests: Identify branches with increased selection
Branch-site tests: Look for selection at specific codons on specific branches
110
give me examples of some fast-evolving genes in humans:
Lysozyme
Sry (sex-determining gene)
BRCA1 (linked to breast cancer)
FOXP2 (speech and language)
111
are synonymous mutations always neutral?
No—synonymous mutations can be under selection for translation efficiency and codon bias
112
Why do highly expressed genes evolve slowly at synonymous sites
because selection favours codons that optimise translation efficiency
113
why is polymorphism roughly independent of population size?
large pops: more selection, less variation
small pops: more drift, less variation
114
Why is the rate of protein evolution approximately constant over time?
Nearly neutral theory: Trade-off between generation time and population size
Selection episodes: Average out over time
115
What does the dispersion index (D) tell us?
D = 1 → Neutral evolution (random substitutions)
D > 1 → Overdispersion: selection or mutation rate variation (more varied rate of substitutions)
D < 1 → Underdispersion: regular pattern, likely purifying selection (less varied rate of substitutions)
116
what is a B chromosome?
an extra unstable chromosome not part of the normal A chromosome set - can be polymorphic and selfish
117
what did darlington and thomas believe about B chromosomes?
they are selfish genetic elements that spread without benefiting the host
118
what does it mean if a genetic elements violates mendelian inheritance?
it is inherited more or less frequently than the expected 50% from each parent
119
what is a selfish genetic element?
a gene that spreads by manipulating inheritance, even if it is harmful to the organism
120
what is intragenomic conflict?
a conflict between genes within the same genome often over inheritance
121
what is the invasion condition for B chromosomes?
2k(1−t)>1
They spread if the transmission advantage outweighs the fitness cost
122
what is meiotic drive?
when certain alleles bias gamete formation to increase their own transmission
123
what is the SD system in drosophila?
a segregation distorter where a toxin (Sd+) and antidote (Rsp+) bias inheritance in a rock-paper-scissors cycle
124
how do selfish genes like medea spread?
by killing sibling embryos that don't inherit the selfish gene
125
how can sex ratio distorters affect populations?
they skew male/female ratios - potentially causing extinction or triggering evolutio. of suppressors or new sex systems
126
what are 3 ways cytoplasmic factors distort sex ratios?
killing males
feminising males
causing asexual reproduction
127
why can selfish genetic elements drive speciation?
they cause hybrid sterility or inviability which acts as a reproductive barrier
128
why are cytoplasmic elements important?
because they are inherited maternally and so only 'care' about female reproduction as males don't pass them on
