chapter 13 - processes of evolution Flashcards
what is evolution?
genetic/phenotypic change in populations from generation to generation
what is Darwin’s theory of selection?
variation among individuals in a population affect their chance of survival and reproduction - natural selection produces evolutionary change
what is artificial selection?
selective breeding of plants/animals by humans
ex. dog breeds
natural selection vs non-selective (neutral) hypothesis using deer example:
natural selection: deer killed by cars differ in some heritable trait(s) relative to deer not killed by cars
neutral selection: the presence of many deer and many cars result in some deer being killed by cars
members of a population must have _____ genetic variation to evolve
heritable
genotype vs phenotype
genotype: genetic makeup
phenotype: physical expression of genes
when do populations evolve?
when organisms with different genotypes survive and reproduce at different rates
do individuals evolve?
no - populations do
define a population
a group of the same species that live and breed in a particular geographic area
members become adapted to where they live
define adaptation
processes by which useful traits evolve
define a gene pool
the sum of all copies of all alleles at all loci in a population
the source of genetic variation
define fitness
the reproductive contribution of a phenotype to next generations relative to other phenotypes
essentially: how many viable offspring does the inheritance of this phenotype produce?
what are the 3 ways natural selection can act on quantitative variation?
stabilizing, directional, and disruptive selection
define stabilizing selection
maintaining the average phenotype
define directional selection
selection that favors traits that vary in 1 direction
define disruptive selection
selection that favors phenotypes at both extremes away from the mean
define sexual selection
acts on characters that determine reproductive success
favors traits that increase chances of reproduction
what are the two types of sexual selection? define them:
inTRAsexual: traits like bright colors, long horns, etc. that improve one’s chances of mating compared to other members of the same sex
inTERsexual: traits that are considered more attractive to the opposite sex
define allele frequency - what is the equation?
the proportion of an allele in a gene pool
p = (# copies of an allele in a population) / (sum of alleles in the population)
p + q = 1
polymorphic vs monomorphic
poly: if a locus as 2 alleles, A and a, that can result in 3 genotypes: AA, Aa, and aa
mono: if a locus only has 1 allele - is a “fixed” allele
define hardy-weinberg equilibrium
a model population in which allele and genotype frequencies do not change
define genetic structure
the frequency of different alleles at each locus and the frequency of genotypes in a Mendelian population
what are the assumptions/conditions required to meet hardy-weinberg equilibrium? (5 conditions)
random mating, infinite population size, no gene flow (migration of genes in and out of the population), no mutation, no natural selection
what is the H-W genotype frequency equation?
p^2 + 2pq + q^2 = 1
where p = 1 allele and q = another allele
what is the H-W model used for?
measuring deviation from the model & mechanisms of evolution within a population
define nonrandom mating
occurs when sexual reproduction is biased in some way
self fertilization is a common form of nonrandom mating
mutation as an evolutionary force?
mutation creates new alleles and is the source of genetic variation
define genetic drift
random variation in allele frequencies
how does population size affect genetic drift?
inversely related
small population = large change by genetic drift
large population = small change by genetic drift
what is bottlenecking?
a temporary decrease in population size
much of genetic variation is lost due to bottlenecking
what is the founder effect?
the reduced genetic diversity which results when a population is descended from a small number of colonizing ancestors
descendent generations exhibit higher frequencies of alleles present in founder individuals
what is a neutral allele?
an allele that doesn’t affect fitness
what kind of alleles are subject to natural selection?
alleles that influence individual fitness (survival and reproduction)
define positive selection
natural selection increases the frequency of an allele that increases individual fitness
define balancing selection
natural selection maintains intermediate frequencies of alleles at the locus because heterozygotes are favored
how do rare beneficial dominant vs recessive alleles affect positive selection?
dominant: alleles increase rapidly with positive selection, but change is fast when common
recessive: alleles increase slowly with positive selection, but change is fast when common
