envs lecture 6 (first 16 slides) Flashcards
what changed human civilization
selective breeding/domestication for agriculture
when did humans harness evolution
11,000 years ago
examples of selective breeding
bred wheat that provided more grain, cows that produced more milk
what did this selective breeding/domestication do
allowed ppl to abandon nomadic lifestyle and settle in communities
quantitative traits
traits that vary continuously and are therefore affected by anywhere from several to thousands of loci
example of quantitative traits
crop yield, milk production, body height
what are polygenic traits
quantitative traits; vary continuously, affected by several/thousands of loci [poly genic cuz multiple genes]
quantitative genetics
study of how quantitative traits are inherited and how they evolve
what effects quantitative traits
both genes and environment interact to affect it
example of domesticated plant
modern corn
where do phenotypic differences in branching pattern between modern corn and its ancestor come from
small number of genetic changes
examples of other differences
size of cob
where do differences in size of cob come from
changes at many loci
example of quantitative trait that varies continuously
human height
what is a normal distribution (varies continuously) curve look like
bell-shaped curve
genotypic variatoin
encoded in DNA: only 4 possible nucleotides, A, T, C, G
is genotypic variation discrete or continuous
discrete
is phenotypic variation discrete or continuous
continuous
what is another word for phenotypic traits
quantitative traits
what kinda distribution for quantitative/phenotypic traits
normal distribution
what kinda curve for quantitative traits
bell shaped curve
how do traits go from discrete genotype to continuous phenotype
many traits affected by many genes AND environmental influences on individual within its lifetime
are quantitative traits affected by many or only a few genes
many genes
example of quantitative traits
height
how many genes is height influenced by
thousands
how else are phenotypic traits influenced
by the environment over lifetime of individual
is this environmental influence genetic or non genetic
non-genetic
what does this variance in environment do to bell curve
smooths it out
can we see genotypes
no
is phenotype or genotype directly seen
phenotype
what is discrete vs continuous phenotype determined by
combo of genetic and environmental variation
what are blue bars
frequencies of phenotypes in population w/o influence of environmental variance
green curves
frequencies of phenotypes for each of genotypes in given population w/ addition of environmental variance
red curves
frequencies of phenotypes for entire population
what does selection act on
phenotype; at level of individual
how do phenotypic distributions become w/ more loci
smoother
what happens w/ more loci
phenotypic distributions become normal
what else can smooth out phenotypic distribution
more environmental variance
what can occur from evolution of allele frequencies w/o addition of new mutations
large changes
important component of evolution of quantitative traits
large changes in quantitative traits can occur by evolution of allele frequencies w/o addition of new mutations
what is a key point for this polygenic quantitative trait
phenotypic distributions for allele frequencies p = 0.25 and p = 0.75 do not even overlap
what can happen w/ multiple loci
can move outside initial range
what do horns on head of horned lizard do
deters predation
where is the natural variation in lizards
variation in length of these protective horns on head of lizard
what does survival vary with for lizards
length of horn
what does fitness function show
lizards w/ longer horns survive better
what do fitness functions show
describe/quantifies how selection acts on quantitative traits
3 basic modes of selection on quantitative traits
directional, stabilizing, disruptive
what does directional selection do
favors change in the mean of a trait in one direction (either toward a greater or lesser value)
what does stabilizing selection do
favors individuals near the population mean
what does stabilizing selection reduce
phenotypic variance in trait –> gives narrower population phenotypic distribution
what does disruptive do
favors largest and smallest
what does disruptive do to variance
increases variance in the trait
example of directional silection
drought led to changes in seed size; larger bills have higher survival ate –> mean beak size shifted and became larger
example of stabilizing selection
human birth weight; infants w/ birth weight much smaller and much larger than average have lower probability of survival
example of disruptive selection
black bellied seedcracker survival depends on lower mandible length; intermediate birds have lowest survival and become less common –> smallest and largest billed ones have highest fitness
what does the type of selection acting on an organism depend on
both phenotypic distribution of organism and phenotypic distribution of food items
when is directional selection at play
most individuals in a population fall within a region of the plot where the fitness function is increasing/decreasing [bill evolves toward a size that is optimal for feeding on hemlock]
when is stabilizing selection at play
if population lies near a peak of the fitness function [tightens the mean around the bill size optimal for feeding on seeds from lodgepole pine cones]
when is disruptive selection at play
if population lies at a low point in fitness function [causes bill size to evolve both larger and smaller towards the two diff sized but available food items]
can selection act on more than one phenotypic trait at once
yeah
correlational selection
selection favors combos of traits
what do evolutionary biologists ask
how and why mean values of traits evolve (often caused by directional selection); important to quantify the strength of selection
selection gradient
measures strength of directional selection on a quantitative trait
relative fitness
individual fitness/mean fitness all individualsh
how do you mesaure selection gradient
measure trait of interest and fitness for a set of individuals who vary in the trait of interest
positive beta
indicates selection favors larger values of the trait
negative beta
indicates selection favors smaller values of the trait
beta is zero means
no directoinal selection
female guppies
prefer males w/ more orange
who has higher fitness among male guppies
males w/ more orange
moderately strong directional selection
-0.5 and 0.5
very strong directional selection
1
is directional selection always strong
sometimes; other times it isn’t
Stronger selection gradient (Beta produces
larger change in size
Lower, but positive gradient (Beta) produces
smaller change in mean trait value
negative selection gradient (-0.5 Beta)
produces a small reduction in size
positive beta selection for
larger size
negative beta selection for
smaller size
