Variation within and among populations Flashcards
(24 cards)
negative frequency-dependant selection
- the less common a phenotype is = higher its fitness
- rare variants have a selective advantage
- specifically due to rarity
positive frequency-dependant selection
-the more common the phenotype is = the higher oits fitness
- e.g. warning colourisation is poisonous species
- does not help maintain variation
heterozygote advantage
-when diff. alleles are favoured under different environmental conditions, heterozygotes may outperform homozygotes
colais butterfly as an example for heterozygote advantage
- certain variants of PGI gene = better able to fly in cold conditions
- others better at flying in warm temps
- heterozygotes can fly a greater range of temps
sick cell anaemia as an example for heterozygote advantage
- incomplete recess, genetic disorder = causes RBCs to deform
- homozygous recessive = phenotype
- heterozygous = mix of deformed and normal blood, resistant to infection by malaria parasite
models of gene flow
- continental island model
- island model
- stepping stone model
- geographic variation
continental island model
- one way gene flow from large continental mainland to smaller island pop.
- allele frequency on island changes at a rate dependant on
1) rate if gene flow
2) diff. in allele frequency between island and mainland
island model
- gene flow among many pops exchanging immigrants w/ each other
stepping stone model
- allow sub-pops to change individuals only with adjacent sub-pops in one or two dimensions
- two sub-pops far apart experience little gene flow
- probability of mating decreases w/ distance
geographic variation
- discrete pops = single large pop or several isolated pop (unlikely)
- continuous populations = phenotypic differences leading to recognition of 2 subspecies
evolutionary constraints
- development of many potential favourable traits prevented by lack of genetic variation
- allele doesn’t exist in the population
- mutation has not given rise to allele that would produce the phenotype
lack of genetic variation
- natural selection cannot act on trait if no genetic variation
- some phenotypes are sure to environment, not genetics
- allele or gene for trait doesn’t exist in the population
trade-offs
- one trait trade offs
- resource allocation
one trait trade offs
- e.g. birth weight
- high birth weight increases survival in first few weeks
- too large = high mortality rate at birth
resource allocation
- trade offs between growth & mortality
- tree species that grow quickly have higher mortality rates
- too much energy put into one to support the other
types of trade offs
- allocation contraints
- functional conflicts
- shared biochemical pathways
- ecological circumstances
- sexual vs. natural selection
gigantism in capybaras as an example of trade offs
theories of two trade offs
1) body size = negative correlation w/ pop size (lack of resources)
2) gigantism achieved via generating higher no. of cells & rates of cell proliferation = increase in likelihood of cancer
microevolution
- change in allele frequencies within pop
- overtime turns to macroevolution
stasis
- some lineages don’t change much in outward appearance for long periods of time
- e.g. horseshoe crab
- some lineages evolve more slowly than others
“rate of character changes” types
- lineages can change slow or quick
- happens in a single direction or reverses
lineage splitting and speciation
- key evolutionary innovation = rapid diversification
extinction
- due to bad genes
- bad luck
Bergmann’s rule
- within a species, individuals in colder climates tend to be larger than those in warmer ones
hypotheses for Bergamnn’s rule
- heat conservation
- heat mortality
- resource availability
- starvation resistance
