10.3 gene pools and speciation Flashcards
get specied
what is a species
a group of organisms that can interbreed to produce fertile offspring
what is a population
individuals of the same species living in the same place and time
what is a gene pool
the set of all variations of all genes present in an interbreeding population
what is allele frequency expressed as in a gene pool?
percentage or proportion
what are the forces of change in a gene pool
random genetic drift
emigration / immigration
selective predation
mutation
founder effect
what is random genetic drift
sudden hostile physical conditions sharply reduce natural pop to v few survivors
eg: cold, flooding, drought
what is mutation + how it is a force of change in gene pool
random, rare, spontaneous changes in the genes occur in gonads, leading to possibility of new characteristics in the offspring
what is the Founder effect
a barrier may arise within a population, instantly isolating a small sample of the original pop – may be carrying unrepresentative selection of gene pool, but will be the basis of the new population – another form of genetic drift
what is the prerequisite for evolution
genetic variation
what happens when populations are isolated from each other?
genetic drift
different selective pressure
cause pops to evolve differently
when differences accumulate –> speciate
what are the different types of selections (3)
stabilising
directional
disruptive
what happens in stabilising selection?
occurs when the existing variations that are beneficial are already common
stabilising selection acts against extremes of a trait
usually remain as one species
what happens in directional selection
occurs when one extreme of a trait offers a survival or reproductive advantage
increases allele freq at one phenotypic extreme, reducing them at other
usually remains as one species
what happens in disruptive selection
most frequent phenotype becomes a disadvantage, individuals at both extremes have better rates of survival and reproduction
population may break into 2 species
what is the Hardy-Weinberg formula
p^2 + 2pq + q^2 = 1
p^2: frequency of homozygous dominant individuals
2pq: frequency of heterozygous individuals
q^2: frequency of homozygous recessive individuals
what is speciation
formation of one or more new species from an ancestral species
what does speciation require
genetic variation, time and selective pressure
what is reproductive isolation
failure of individuals from two populations to mate and produce fertile offspring
what does reproductive isolation result in
elimination of gene flow between the populations
what are the 3 main isolation barriers
geographic
behavioural
temporal
what happens in geographic isolation
separation of populations by a physical barrier reducing/ preventing gene flow
allopatric speciation: new species emerging during geographic separation of a population from other populations
what happens in behavioural isolation
any genetically-influenced difference in behaviour that acts to reduce / eliminate gene flow between portions of a population
sympathetic speciation: when a portion of a population develops into a new species while living in the same geographic area as the ancestral population
what happens in temporal isolation
any shift in timing of a behaviour that acts to reduce or eliminate gene flow between portions of a population
occurs when portions of a population are reproductively actively at different times
eg: portions of the population may mate or flower at different times of day / seasons
rates of speciation (3)
GRADUALISM
ABRUPTLY
PUNCTUATED EQUILIBRIUM
GRADUALISM
occurs when major changes are the cumulative product of slow but continuous minor changes
mutation or immigration occasionally introduces new alleles to the gene pool, which are then acted on by natural selection, becoming more common or disappearing
PUNCTUATED POLYPLOIDY
implies long periods without appreciable change and short periods of rapid evolution
species generally stable during long periods while stabilising selection works to maintain the existing phenotype of the species
however, periods of stability are punctuated by rapid busts of phenotypic change
often result of major upheavals such as long-term climate shifts / arrival (through immigration of evolution) of a new species with strong ecological impact
stabilising selection would shift to directional or disruptive selection
what is polyploidy
refers to the presence of more than two complete sets of chromosomes in a cell
can be caused by the total non-disjunction of chromosomes during mitosis or, most commonly, meiosis 1
