Week 1 Flashcards
Fisher
The modern synthesis
several genes can contribute to a single trait
Positive selection
NS that increases the frequency of a favourable allele
Negative selection
NS that decreases the frequency of a deleterious allele
balancing selection
acts to maintain two or more alleles in a population
stabilising selection
maintains the status quo and acts against extremes
directional selection
leads to a change in a trait over time
artificial selection
form of directional selection
successful genotypes are selected by breeder, not through competition
Disruptive selection
operates in favour of extremes and against intermediate forms
intrasexual selection
members of one sex compete with one another for access to the other sex (fighting)
intersexual selection
females choose thier mates
males compete for the attention of females with bright colours and advertisement displays
biological species concept
species are group of actually or potentially interbreeding populations that are reproductively isolated from other such gorups
Morphospecies concept
members of same species usually look alike, have similar DNA sequences that are distinct from other species
cryptic species
organisms that had been traditionally considered as belonging to one species because they look similar, but turn out to belong to two species because of a distinction at the DNA sequence level
ring species
species with populations that are reproductively but not genetically isolated
gene exchange occurs indirectly through intermediate populations
ecological species concept
there is a one-to-one correspondence between a species and its niche; impossible for two species to coexist in same location if their niches are too similar because competition will lead to extinction of one of them
phylogenetic species concept
members of a species all share a common ancestry and fate; members of a species have one common ancestor; useful in asexual species; limited use
Pre zygotic isolating factors
behaviourally isolated gametic isolation mechanical incompatibility temporal isolation geographic or ecological isolation
post zygotic isolating factors
genetic incompatibilities
two ways by which populations become allopatric
dispersal and vicariance
dispersal
some individuals colonise a distant place far from the main source population
vicariance
geographical barrier arises within a single population, separating it into two or more isolated populations
vicariance-derived speciation is easier to study as easier to date
peripatric speciation
few individuals from a mainland population disperse to a new location remote from original population and evolve separately
change accumulates faster in the isolated populations than in original population (genetic drift more pronounced)
Adaptive radiation
bout of unusually rapid evolutionary diversification in which NS accelerates the rate of both speciation and adaptation; Occurs when there are many ecological opportunities available for exploitation
co-speciation
speciation that occurs in response to speciation in another species
host-parasite speciation
sympatric populations
for speciation to occur sympatrically, NS must act strongly to counteract the homogenising effect of gene flow
no geographical separation
BSC does not apply to
asexual or extinct organisms
speciation
occurs when two populations that are genetically diverging become reproductively isolated from each other
cannot produce viable, fertile offspring together
allopatric population
populations geographically separated from each other
peripatric speciation is a type of
dispersal
order of M
molar milli molar micro molar nano molar femto molar
n=
CV
m=
n x Mw
Darwin’s two observations
members of a population often vary in their inherited traits
all species can reproduce more offspring than their environment can support (struggle for survival)
what is changing over time in NS
the inherited traits of a POPULATION
Darwin’s two inferences
those with higher survival rate contribute more offspring to next generation
accumulation of favourable traits in the population over many generations
heritable variations in traits
is randomly produced through mutation and sexual reproduction
