3.5 speciation Flashcards
mutation
a permanent and random change in the DNA base sequence
allele frequency
how common an allele in a population is
gene pool
total set of alleles in a population
genetic drift
the random change in allele frequency due to chance events. it is necessary for evolutionary change
founder effect
when a group of individuals from an existing population move to a new area and reproduce isolated from the original population. it is likely to cause fixed or lost alleles, leading the founding population to have little genetic diversity
bottleneck effect
the drastic decrease of population numbers due to a sudden catastrophic event - causing an under-representation of alleles in the gene pool
migration
the movement of individuals from one poplation to another, hence alleles. it usually causes genetic drift. when migrating individuals interbreed into a new population, the genetic variation is decreased, which may create new allele combinations and eliminate a unique population
emigration = leaving, immigration = entering
gene flow
the movement of genes/alleles between different gene pools
directional selection
favours 1 phenotype, is against the other
disruptive selection
favours both extremes, goes against the average phenotype
stabilising selection
favours the average phenotype, goes against both extremes
speciation
a term that describes how species form. it occurs when there is little gene flow, possibly due to reproductive isolation. it can occur slowly over time or instantly
species
a group of interbreeding, or potentially interbreeding, individuals which give rise to fertile offspring
allopatric speciation
a type of speciation due to geographical barriers and/or isolation. it causes differences to accumulate, which are due to different selection pressures, mutations and natural selection. overtime, the populations no longer recognise each other
sympatric speciation
where populations become distinct species in the same geographical location. since there is no geographical barriers, the effect of reproductive isolating mechanisms are greater. it tends to take more time to accumulate differences due to overlapping selection pressures and gene flow
prezygotic isolating mechanisms
occurs before fertilisation
includes: temporal, ecological, gamete mortality, behavioural, mechanical/structural
spatial RIMS cause isolating mechanisms to develop
postzygotic isolating mechanisms
occurs after fertilisation
includes: hybrid sterility, hybrid inviability, hybrid breakdown
temporal
organisms reproduce and are active at different times. ex. seasonal flower bloomings and diurnal vs nocturnal animals
ecological
populations live in different habitats or are in different niches
gamete mortality
due to chemical differences in the egg and sperm (or pollen) , the gametes cannot fuse to become a zygote
behavioural
organisms have different courtship behaviours, ex. singing and dancing. there are unique to each species and are unrecognisable to others
structural/mechanical
the variation of colour, pattern, size etc… is different for each species and unattractive to another. for insects usually, mating apparatuses are also unique and specific, hence will not fit together physically
hybrid sterility
healthy offspring can be produced, however, it will be sterile
hybrid inviability
the zygote cannot be fully developed, usually resulting in stillbirth or miscarriages. the offspring may be born, but will die before maturity
hybrid breakdown
the first generation of offspring are fertile, however, their offspring are infertile/inviable
reason for rims
to preserve a species and makes the production of offspring expend the least amount of energy, which is favourable
autoploidy
polyploidy occurs in the same species due to non-disjunction. usually the organism will self fertilise
alloploidy
polyploidy occurs in different species, which are closely related. hybrid will not form if the species aren’t close enough. non-disjunction usually has to occur twice
diverging evolution
an ancestral parent species split into 2 or more species, resulting in evolution. usually caused by rims (mostly prezygotic), selection pressures, and geographical isolation. the species produced will be quite similar due to the common ancestor
adaptive radiation
rapid diverging evolution, causing large phenotypic and ecological diversity. several species will be formed by a common ancestor, which exploit different niches. it is usually in response to a new habitat, decrease in competition, or development of a new feature
convering evolution
evolution of similar traits in unrelated species, usually the result of occupying similar habitats or ecological niches - which hence select for similar features. species don’t usually breed together
parralel evolution
when species formed through diverging evolution from a common ancestor develop similar features (usually just one) due to changing selection pressures
analogous
same function in species but did not evolve from the same ancestor. for example, bat and bird wings. they both fly but they aren’t related and the structure of the wings are different
homologeous
species from the same ancestor have features that have different functional apsects. for example, humans have 5 fingers, bats have 5 segments in their wing, and whales have 5 bones in their fins
