envs lecture 6 Flashcards
what can we predict
how much evolution will result from selection acting on a trait / how much evolutionary change is caused by selection acting on a trait
what do evolutionary biologists need to know
how much the mean of a given trait will evolve if there’s directional selection
how can we predict how much evolutionary change given by directional selection
by calculating the difference between the mean of a trait at start of new generation and mean of the trait now
what is Breeders equation used for
to predict the amount of evolutionary change that results from selective breeding
basically what is Breeders equation
evolution by directional selection from one generation to the next
what does rate of evolution depend on
strength of inheritance and strength of directional selection
what is h^2
heritability
what happens if h^2 = 0
no resemblance b/w parents and offspring
what happens if h^2 = 1
parents and offspring identical
what is the slope of the line equal to
heritability
what does Breeders equation show the difference between
difference b/w mean trait in next generation and now
what does each point on the graph represent
mean of all offspring in single family plotted against mean of their parents
what does no slope mean
no relationship b/w mean of parents and mean of offspring in a given trait —> heritability is 0
what does straight/diagonal line slope mean
heritability is 1, parents and offspring are identical
equation relating phenotypic, genetic, and environmental variance
Vp = Vg + Ve
what is Vp
overall phenotypic variance
what is Vg
genetic variance (phenotypic variation caused by genetic variation)
what is Ve
environmental variance components
what does gene expression depend on
age and tissue type, interactions among gene loci, and direct environmental influence
examples of variation in phenotype caused by both genes and environment
human height (heritable but influenced by diet)
what is overall phenotypic variation result of
combo of genetic variance in a trait and environmental components
what does partitioning genetic variance do? why do we do it?
distinguishes role of heredity vs. environment
what is variance of genetic components of Vg
Vg = Va + Vd + Vi
what is Va
additive genetic variance
what is additive genetic variance
the average effect of substituting one allele for another
what is Vd
dominane variance
what is dominance variance
variance due to dominance of alleles at same locus
does dominance variance contribute to evolutionary change
nope, because heterozygotes are not intermediate; they’re gonna exhibit phenotype of dominant allele
what is Vi
epistatic interactions of alleles at different loci
what is epistatic interactions
effect of one allele depends on a second allele
what contributes to evolutionary change
only Va (additive genetic variance)
basically what is genetic variance determined by
genetic interactions within individuals averaged over the population
does Vd cause evolutionary change?
no
does Vi cause evolutionary change
nope
do heterozygotes exhibit an intermediate phenotype
nope
what does the locus exhibit
overdominance
what is overdominance
heterozygous phenotype exhibits a more extreme/different phenotype from either homozygote
in this plant example, what happens to the heterozygotes
they are taller than either homozygotes
what happens if we incorporate selection and all short plants die
only heterozygotes are left
what happens if only heterozygotes are left
frequency of alleles do not change; so no evolutionary change in overdominant locus
what is dominance variance
heterozygotes are not intermediate w/r to homozygote phenotypes
what does additive genetic variation do
only variance that contributes to how fast a population evolves in response to directional selection
why doesn’t selection cause evolutionary change in this case
for most traits, additive genetic variance is larger than dominance variance and epistatic variance
what’s up w/ traits with high genetic component (lot of genetic variance)
high heritability
what does it mean to have a high genetic component
a lot of genetic variance
examples of traits w/ high genetic component
traits like height and length
what’s up w/ traits that require lots of resources
sensitive to environmental variation
describe heritability of traits that are sensitive to environmental variation/require hella resources
don’t have as high of heritability
examples of traits that require hella resources (not as high heritability)
traits like body weight, litter size, age of puberty
describe heritability of fecundity and life history characters
low heredity
why is heritability of fecundity and life history low
b/c they are tied to resource availability –> environmental variance
what does environmental fluctuation do
maintains variation and heritability
describe ground finches from Galapagos islands and variation/heritability
in drought, food supply is low and seeds are big and hard –> body and bill sizes are large
after el nino –> hella small soft seeds available –> smaller bird w/ smaller bill is favored
what does this fluctuating environmental variance lead to
variance in selection acting on diff phenotypic traits
what is one of the most basic questions we can ask about genetics of quantitative traits
what loci contributes to these traits
what gene regulates melanic coloration/production of melanin
MC1r gene
what does MC1r gene produce
melanocortin receptor 1 protein
what is MCTr gene an example of
parallel phenotypic evolution
what is parallel phenotypic evolution
changes that are parallel at the level of the gene but but at level of nucleotide
what does parallel phenotypic evolution lead to
changes occur in diff parts of gene in diff organisms, but still same result –> melanization in all of them
example of melanic parallel phenotypic evolution
AA substitutions in diff parts of protein cause melanization in snow goose, jaguar, mice, etc.
what is the genetic basis of this polymorphism (some yellow some melanic) in coloration/melanin
few amino acid substitutions in MC1r protein
what are other amino acid subs in MC1r important for
encoding for red hair in humans and melanism in mice and chickens
is MC1r gene also involved in snow geese and arctic skuas light and melanic morphs?
yup
what is tied to melanin polymorphism in lesser snow goose and parasitic jaeger
single amino acid substitutions
what is the association b/w particular mutations and
degree of melanism
what do they mean by particular mutation
copy number of variant MC1r alleles
what does heterozygotes being intermediate and having multiple copies of gene mean
makes the trait quantitative rather than mendelian
why do snow geese exhibit wide array of phenotypes rather than just 3
Heterozygotes are intermediate and in some cases there may be multiple copies of this gene, which makes the trait become effectively quantitative rather than mendelian
