Exam 1 Flashcards
Darwin’s postulates
Individuals vary in phenotypes, variation can be passed down (heritable), each generation more offspring produced than can survive, the variants that result in better survival and reproduction will be better represented in next generation (differential survival and reproductive success)
Modern Synthesis
Fusion of Darwinian evolution and Mendelian genetics, lead to population and quantitative genetics. Unified macro- and micro-evolution. Highlighted other mechanisms of evolution beside natural selection.
Evolutionary genomics
sequencing entire genomes
Group selection
for the good of the group
Holes in modern synthesis?
Epigenetics, evolutionary developmental biology, meta organisms, prokaryotes
Epigenetics
stable phenotypic changes that do not involve alterations in the DNA sequence
evo-devo biology
compares the developmental processes of different organisms to infer how developmental processes evolved
How does evo-devo clash with modern synthesis?
Highlights an important role for non-coding and regulatory
variation in the evolution of organism body plans. Mutations in
“master” regulatory genes may affect large changes in morphology.
meta-organisms
metazoans as “metaorganisms”. These
include the larger organism plus all its endosymbionts (mostly
bacteria). Coevolution between the genomes of endosymbiotic microorganisms and the genome of the host is viewed as a central
consideration in evolutionary change (you can’t understand one without the other).
natural selection
variation in relative fitness within a population
absolute fitness (individual)
the number of offspring produced by that individual in its lifetime
absolute fitness (population)
the population growth rate (absolute fitness of individuals added across all individuals per generation)—this determines the fit of the population to its current environment
relative fitness (individual)
number of offspring produced in that individual’s lifetime relative to other individuals in the population - what matters when in comes to adaptive evolution, because it causes changes in gene frequencies and phenotype distributions
Selection differential (S)
Strength of selection. S=μ selected - μ1. The phenotype selected for minus the mean phenotype
univariate breeder’s equation
R = h^2S. R=response to selection, h^2=narrow sense heritability, S=selection differential/strength of selection
fitness landscape
relationship/covariance between trait value and relative fitness
multivariate breeder’s equation
ΔZ = Gβ. Z= response (change in the trait in the next generation), G= Matrix (correlation between traits), B=selection gradient (coefficient of selection on multiple traits with itself)
Selection model terms
linear, non-linear (univariate), non-linear (bivariate)
linear terms
test for positive and negative directional selection on trait means
non-linear - univariate
test for selection on trait variance (disruptive or stabilizing selection)
non-linear - bivariate
test for correlational selection on pairs of traits
what does positive correlational selection mean for the trait values?
favors similar values of traits (low and low, high and high, etc.). negative favor different values (high and low, etc.)
neutral theory
most SNP variation occurs because of neutral processes does not negate phenotypic plasticity
narrow sense heritability (h^2)
the proportion of phenotypic variance that is due to additive genetic variance (additive genetic variance divided by total phenotypic variance)
h^2=
Va/Vp. Va = additive genetic variance. Vp = total phenotypic variation
epistasis
the effect of a gene mutation is dependent on the presence or absence of mutations in one or more other genes, respectively termed modifier genes. In other words, the effect of the mutation is dependent on the genetic background in which it appears.
non-additive genetic variance
dominance, epistasis
Ve=
environment, genotype (plasticity)
Vp=
Va+Vna+Ve
Why do we only care about additive genetic effects?
includes intermediate values for heterozygotes, selection can actually act on it, while non-additive genetic variance masks the underlying genotype
What are the proximate causes of genetic correlations?
linkage disequilibrium, pleiotropy
linkage disequilibrium
non-random association of alleles at different loci in a given population
pleiotropy
one gene influences two or more seemingly unrelated phenotypic traits
what is the ultimate cause of genetic correlations?
correlational selection
Gmax
dimension in trait space for which there is the maximum amount of genetic variance, axis of Matrix over which G is maximal, eigenvalue, path of least resistance
genetic drift
change in allele frequency in a population due to random sampling of that population (such as random mortality)
gene flow
movement of genes across space from one population to another
chances of a brand new mutation coming to fixation in a population
1/2N (N=population). Two alleles per individual
mutation-selection balance
equilibrium in the number of deleterious alleles in a population that occurs when the rate at which deleterious alleles are created by mutation equals the rate at which deleterious alleles are eliminated by selection. Can be overwhelmed by drift in small populations
population bottleneck
sudden drop in population size that noticeably alters allele frequency
inbreeding depression
deleterious alleles increasingly combined into homozygous genotypes
background selection
losing beneficial alleles because selection acts against the deleterious alleles in the same individual
founder effect
small subgroup breaks off from larger ancestral population and colonizes a new environment (often invasive species)
positives of founder effect
novel genetic recombinations that may not have happened in a larger population, possibly allowing for a new phenotype that increases fitness in new environment
shifting balance model
genetic drift is required to cross fitness valleys and occupy new adaptive peaks
positives of gene flow
possible transfer of beneficial genes, good for small populations to introduce more genetic variation and novel genes
cons of gene flow
bad if maladapted for environment and gene swamping occurs, also bad if hitchhiking genes, mess with existing linked genes
gene swamping
high levels of gene flow can knock population off its local adaptive peak
migration selection balance
equilibrium, natural selection balances maladapted genetic material received from gene flow
genetic rescue
gene flow can provide small populations with fresh genetic variation
evolutionary rescue
new mutation rescues a small, deleterious allele-filled population
forces of evolution
mutation, natural selection, gene flow, genetic drift
There are small populations of grasshoppers living on two islands separated by 1 km of ocean. The environments of these islands differ to the extent that both populations are under equal magnitudes of selection, but in opposite directions. These populations exchange small numbers of migrants each year as individuals will sometimes get caught in storms and blown to the other island. Is it likely that these populations will speciate? How do drift, gene flow, and selection, respectively, influence the probability of speciation?
Though it depends on how small these populations are, how many migrants are exchanged, and whether the migration even leads to gene flow, these two populations of grasshoppers will likely not speciate. Genetic drift would decrease genetic variation in each population, likely leading to the accumulation of deleterious alleles because these populations are small. Though the number of migrants is small, gene flow from the migrants would likely provide a much needed source of genetic variation to counteract the deleterious effects of genetic drift. Gene flow is the largest reason speciation would be unlikely to occur. Genetic drift would weakly increase the likelihood of speciation, due to random changes in genomes likely being different between the two populations, but drift would have a stronger effect of decreasing the chance of speciation, due to increasing the need for genetic variation from migrants. Even though natural selection would select against the traits received from the source population as these individuals are maladapted for the new environment, there would still likely be enough exchange of genetic material to prevent speciation. Therefore, natural selection would increase the probability of speciation, but likely not enough for speciation to actually occur.
gene swamping, critical threshold
knock off adaptive peak, but also probably prevent local extinction
role of genetic architecture in the relationship between gene flow and local adaptation?
genetic architecture can provide resistance to gene flow via processes like inversion.
What role does gene flow play in the maintenance of genetic diversity within populations?
gene flow helps prevent fixation by introducing genetic variation
Under what conditions should gene flow enhance vs inhibit local adaptation?
Enhance when the environment is variable, allowing for adaptation. Inhibit when environment is stable, knocking off adaptive peak.
genetic architecture
physical genetic basis of phenotypes, such as where genes are located, how they are linked, etc.
how does gene flow affect linkage?
gene flow can break up linkage if from at least somewhat adapted population, but reinforce it if from maladapted population, as it leads to higher correlations in the matrix
how can gene flow be an agent of selection?
by spreading advantageous alleles, increasing the genetic variation upon which selection can act
adaptive landscape
at a population level, relationship between absolute fitness and mean phenotype
peak shift
jump from a local peak to another local peak or the global peak
factors that influence the adaptive landscape
environment, intrinsic features of organism, and frequency dependence
“proof” of adaptive landscape
convergent evolution - distantly related organisms evolving in similar conditions will often evolve to be very similar, even though they evolved independently. The further apart in time, the less likely for convergent evolution, but adaptive landscape still influences organisms’ evolution
how might phenotypic plasticity be incorporated into adaptive landscape?
can help explain peak shifts, multiple peaks, and fluctuations. phenotypic plasticity can be a trait itself, and selection can favor it
what are the challenges of understanding macroevolution with adaptive landscape framework?
the time needed for macroevolution is hard to capture with adaptive landscape. However, fluctuations only slow evolution, not stop or change overall direction. Sometimes AL is most helpful tool to think about longterm evolution, as large trends within AL tend to be stable
Gmatrix
central concept in understanding the inheritance of multiple traits, each of which is affected by many genes, consists of additive genetic variances for the traits on its main diagonal and set of additive genetic covariances between traits (arising from pleiotropy and linkage disequilibrium) as its off-diagonal element
Gmatrix
central concept in understanding the inheritance of multiple traits, each of which is affected by many genes, consists of additive genetic variances for the traits on its main diagonal and set of additive genetic covariances between traits (arising from pleiotropy and linkage disequilibrium) as its off-diagonal element
