4th weekly quiz Flashcards
what are the steps to test for adaptation
observation
experiments
comparisons
what does a null hypothesis assume
there is no relationship between the 2 variables being tested
what is the comparative method
comparisons across species to test predictions
what is the issue with using stats with evolution
species are not independent data points
what is a type 1 error
false positive
type 2 error
fasle negative
what is the main method of the comparative method
phylogenetically independent contrasts (PICs)
what is biological scaling (allometry)
the change in organisms in relation to change in body size
what do independent contrasts summarize
summarize the amount of character change across each node in the tree
what can independent contrasts be used to estimate
rate of change across a phylogeny
why might adaptation be absent
genetic constraints
physical constraints
phyletic contraints
trade offs
what are the genetic constraints on adaptation
even if selection should select in favour of the hypothetical trait, it can’t
inertia
what is inertia in evolution
limitations on future evolutionary pathways that have been imposed by previous adaptations
what are physical constraints on evolution
when like certain traits must be there to function (?)
what is a phyletic constraints
historical restrictions based on the evolutionary history of the species
what are the trade off constraints on adaptation
trade off between allocation of energy towards growth vs reproduction
what is multi-level selection
how certain traits can increase fitness at one level and decrease fitness at another level
what is the main function of sex
to allow alleles at one locus to float freely to another locus from generation to generation
why is sex a costly behaviour
- complicated (finding a mate)
- costly (lots of courting and competition)
- dangerous (risk of predation and disease)
- recombination scrambles genotypes (bad if genotype is already in a favourable combination)
- delays reproduction (takes longer)
- genome dilution (females on contribute 1/2 their genetic material)
what is syngamy
fusion of egg and sperm
what is the two-fold costs of sex
less reproduction
parthenogenetic females theoretically have more offspring than sexual females
how does hardy Weinberg genetics and the genetics of selection treat each locus?
what is issue with it?
as independent
alleles are linked in chromosome
what is a haplotype
a group of genes within an organism that are inherited together from a single parent
what is linkage disequilibrium
the non random association of alleles at different loci in a gene population
what does sex do to linkage disequilibrium
sex breaks linkage disequilibrium down
what is linkage equilibrium
when haplotype frequencies in a population have the same value they would if the genes at each locus were combined at random
what is linkage disequilibrium caused by
often by alleles being physically linked (though not necessarily)
do processes that affect allele frequencies (drift, selection) affect other loci
yes
what are the key features of sex
can combine beneficial mutations on same chromosome
reduce linkage disequilibrium
how are recombination rates effected as distance between loci increase
increase
how linkage disequilibrium react as loci become farther apart
decrease
what is clonal interference
the competition between lineages arising from different beneficial mutations in an asexually reproducing population
what does recombination tend to do to genotypes in relation to other genotypes
randomize the genotype
what creates linkage disequilibrium
genetic drift
selection on more than one trait at a time
sampling two populations with different compositions
creation of new mutations
how does drift effect linkage disequilibrium
can both create it and reduce it
how does linkage disequilibrium effect rate of change of populations
can slow it
how can linkage disequilibrium slow evolution in populations
if beneficial mutations happen near “bad” mutations since selection acts on phenotypes so the sum of selection coefficients
strong selection at a loci can drag along alleles on the same loci
what is evidence of a strong linkage disequilibrium in a well mixed population (where HWE should hold) evidence of
recent natural selection
what is sex
bringing haplotypes together for recombination
how does sex speed up evolution
breaks up genotypes
what are some alternatives to sex
vegetative (asexual) propagation
parthenogenesis
gynogenesis and hybridgenesis
what is vegetative (asexual) propagation
development of offspring from part of an adult body
what is parthenogenesis
meiosis suppressed development of offspring from unreduced egg in female
what is gynogeneisis and hydidogenesis
meiosis is suppressed
development of offspring from faux fertilized egg
what sex are the offspring resulting from gynogeneisis and hybridogenesis
all female
what are all asexual vertebrates the result of
hybridization of 2+ other species
why do asexual species go extinct more often
can’t adapt fast enough
they actively deteriorate
what is muller’s rachet
process through which, absence of recombination, an accumulation of irreversible deleterious results
what is genetic load
presence of unfavourable genetic material in the genes of a population
when is muller’s ratchet fastest
in a small populations with high mutation rates and mildly deleterious mutations
what does sex do to muller’s ratchet
breaks it through recombination and outcrossing
why is sex advantageous in the long run
asexuals go extinct more often
why are asexuality immediately advantageous
cost of males
what is the short term benefit of sex
recombination has postive s since it creates variation which is selected for in environments that vary
what are the two main theories for short term benefits of sex
tangled bank
red queen
what is the tangled bank theory
spatial heterogeneity in environments favour sex
- if offspring disperse, the variation created by sex makes them more likely some will be successful in varied environments
- if offspring dont disperse: less likely for competition between siblings
what is the red queen theory
species must adapt and evolve not just. for reproductive success, but also for survival since competing organisms are evolving
what do tangled bank and red queen both predict about when sex is favoured
it is favoured at high stable densities (lots of competition)
when is asexuality most common
in poles and other harsh conditions
what are asexuals often good at
being early colonizers of novel habitats because of rapid growth rate
when should recombination be most common
when litter size is large
within-brood variation is possible
is asexuality rare or common
rare
what does long term mutation load and environmental variation favour (sexual vs asexual)
sexual
how does recombination effect speed of evolution and why
speeds it up
by allowing for more effective selection
does recombination allow purging of mutational load
yes
what is quantitative genetics
study of traits affected by many genes and the environment
what is a population
vague term denoting a set of demographically linked individuals
are interactions stronger between members of the same population or different population
same
what can total variation be broken down into
genetic variation (Vg) environmental variation (Ve) genotype by environment variation (Vge)
what is genetic variation
variation due different allele/genes
what is genetic variation supplied by
mutations
what is environmental variation
variation due to different environments
is environmental variation heritable
no
what is genotype by environment variation
variation due to interactions between genes and the environment
what is a fitness function
relationship between trait value and relative fitness
what is relative fitness
probability of contributing to next generation
what are the different types. of fitness functions
directional selection
disruptive selection
stabilizing selection
what is directional selection
selection for one extreme over the other extreme
how does directional fitness affect the mean phenotype
causes a change in it
what is disruptive selection
selection for both extremes, against moderate traits
how does disruptive selection affect mean phenotype and distribution
broadens distribution but doesn’t necessarily affect mean
what is stabilizing selection
selection for moderate traits, against extremes
how does stabilizing selection affect phenotypic mean and distribution
narrows distribution but doesn’t necessarily change mean
why is recombination (sex) necessary for quantitative genetics
recombination allows us to think of alleles as free from all genetic background and to be able to talk about their mean and additive effects
how much of a population’s variation is due to Vg
50-80%
what does Vp stand for
phenotypic variation
what is Va
additive variation
what is heritability
the proportion of variation (Vp) in a trait that is due to additive variation in genes (Va)
proportion of variation by all genetic effects (Vg)
measure of how well differences in people’s genes account for differences in their traits
what does additive genetic variation determine
degree of resemblance between relatives
determines the response of a population to selection
what does Va estimate
heritability of a trait in a specific single population
what is h^2
= ability to predict differences in offspring based on differences in parents
what is h^2 due to
only additive components of alleles underlying it
what is mid parent value
parental phenotypes
what does it mean when h=0
no heritability
is heritability environment specific
yes
what determines the evolution of a trait
heritability combined with strength of selection
why is heritability for fitness related traits low
since fitness related alleles have fewer genetic variation (since selection lowers variation) = lower heritability
