if individuals of a particular phenotype survive and/or produce more offspring than others: (2)
- phenotype must be a product of the genotype (i.e. heritable)
- genotype vary in their fitness
rate of change
a function of selection intensity
fixation meaning
only allele in 100% of population
changes in genotype frequency (allele frequencies have not changed but genotype frequencies have); what could reset the genotypes back to start?
1 generation of random mating
patterns of selection (4):
- recessive vs dominant alleles
- heterozygotes favoured
- homozygotes favoured
- frequency-dependent selection
patterns of selection: (1) recessive vs dominant alleles
individuals with +/+ or +/- are normal, -/- do not survive (recessive lethal)
patterns of selection: (1) recessive vs dominant alleles:
selection is rapid/slower when a recessive allele is ___(2) and lethal
selection is rapid when a recessive allele is common and lethal
selection is slower when a recessive allele is rare and lethal
patterns of selection: (2) heterozygotes favoued
heterozygote advantage/superiority: the fitness of heterozygotes is greater than any homozygote
(the equilibrium point depends on selection pressure)
patterns of selection: (3) homozygotes favoured
heterozygote inferiority/underdominance - the fitness of heterozygote < fitness of either homozygote
patterns of selection: (4) frequency-dependent selection
ex. red/yellow orchids (after pollinator is fooled, they try to switch between flow colour to look for nectar); if small % of population, that colour’s pollen will be picked up more!
higher reproductive success if lower frequency in colour
inbred stock meaning
starting stock that were all genetically identical to each other (i.e. no genetic variation)
mutation-selection balance
- many mutations are deleterious
- selection may remove deleterious alleles but mutations may re-introduce them, hence they persist
- mutation-selection balance = rate of new copies of a deleterious allele produced by mutation EQUALS rate of selection removing them
gene flow (migration) may be caused by:
- dispersal - one-way movement of a juvenile individual away from place of birth
- transport of pollen, seeds, spores by any means
what does gene flow tend to do?
- it tends to homogenize allele frequencies among populations
- tends to prevent evolutionary divergence of populations
- may function to decrease the population-level impact of natural selection and/or other mechanisms of evolution
-> if populations all exchange at an equal rate, eventually each population will on an equilibrium frequency of alleles (w/o other evolutionary forces)
-> would equal avg allele frequencies of the populations
Fst meaning?
a measure of variation among populations in allele frequencies at a locus
- “fixation index”
Fst value range, can be computed for how many populations, what does it decrease with?
range: 0-1
0 = all populations have identical allele frequencies
1 = no alleles are shared among populations
can be computed for 2 or more populations
gene flow reduces Fst among populations
evolution: (4) by genetic drift
- random changes in allele frequencies from one generation to the next (sampling error)
- does not lead to adaptation
what can genetic drift lead to? (2)
- fixation
- decline in heterozygosity
effective population size meaning
- ideal theoretical population size that would lose heterozygosity at the same rate as the actual (census) population size (assume everyone breeds)
- almost always lower than the actual
- WHY: not everyone in population breed
what is the probability of fixation of one allele or another?
depends on starting frequency
- A=0.6, B=0.4;
- probability that drift will fix A is 0.6, and B is 0.4
demographic events that can cause genetic drift: (2)
- founder events
- bottleneck
found event meaning
occur when a population is founded by a small group of individuals
- may considered a form of genetic drift
bottleneck meaning
a sharp decline in population size followed by population recovery
H-W assumes random mating (panmictic) includes (4)
- inbreeding
- outbreeding
- positive assortative mating
- negative assortative mating
- does not on its own change allele frequencies
- does impact genotype frequencies, so in conjunction with natural selection, can have important evolutionary consequences
