adaptation 4 - quantitative traits Flashcards
(42 cards)
Quantitative traits
Are influenced by the combined activity of several genes (polygenic)
Often influenced by the environment, to varying degrees
Have patterns of continuous trait variation, rather than having discrete categories
Often have a mean and variance
possible barriers for response to changing conditions
pikas: low elevation is a barrier to moving to other more northern mountain ranges, bc cant stand heat
meaning of adaptation in 336
undergoing genetic change
in other contexts, used instead of acclimating
distribution of traits affected by different factors
general normally distributed
Why are quantitative traits normally distributed?
Bc affected by multiple loci and environmental factors
Evolution of traits with normal distributions by natural selection
- trait must vary btwn individuals
- trait must affect fitness
- trait must be heritable
3 forms of selection on quantitative traits
- directional selection
- stabilizing selection
- disruptive selection
related to how selection impacts one generation
Fitness function
shows fitness of individuals with certain “values” of a quantitative trait
Directional selection
individuals with more severe “values” of a quantitative trait have greater fitness
variation shifts in one direction or another
stabilizing selection
variation decreased
disruptive selection
variation increases
average effect
determines how much the mean of a trait Z changes when we know an individual carries this particular allele, assuming PAIRED AT RANDOM with another allele from population
Breeding Value
(A)
Breeding value of an individual (or genotype) measures the average contribution of that individual to the trait mean of its offspring, if crossed with an average range of mating partners
Breeding value equation
(mean of pop) + 2*([mean of offspring] - [mean of population])
what does breeding value measure
the degree to which an individual’s phenotype is expected to be transmitted to their offspring
what is phenotype a function of
P = genes + environment
BREAKS DOWN Into
(A + D + I) + E
What could genetic component of phenotype be broken down into?
A - additive genetic effects (breeding value)
D - dominance effects
I - Interaction effects (epistasis btwn loci)
def. additive effects of alleles
average effect of all alleles that contribute to a phenotype
def dominance effects
effects of dominance interactions among alleles at each locus
def epistasis
The effect of interactions among alleles at different loci
why do we focus on additative effects in the evolution of quantitative traits
non-additive effects are disrupted every generation therefore no predictable effect on offspring
env. not genetically based
therefore, natural selection acts on additive effects
Artificial selection vs natural
breeders focus on picking individuals for crosses to move the mean trait values/change traits of group
natural selection acts on differential success of individuals with different trait values, affects how a trait mean will change in response
phenotypic variance
(VP)
describes the variability among a set of individuals for a particular trait
NOT always do to genetic differences (VG), not all genetic differences passed to next generation (VA)
