Gene Pools and Speciation

Gene Pools & Speciation Gene Pools Define gene pool Sum total of all genes (and their alleles) present in an interbreeding population ………………………………………………………………………………………………………………………………………………….......... ………………………………………………………………………………………………………………………………………………….......... Outline a factor that influences genetic drift and identify two conditions by which this factor may occur Genetic drift is a change in composition of a gene pool due to random events and is impacted by population size ………………………………………………………………………………………………………………………………………………….......... Size affects stability of allele frequencies (high drift in small populations / low drift in large populations) ………………………………………………………………………………………………………………………………………………….......... Population bottlenecks (occur when an event reduces population size by an order of magnitude) 1. …………………………………………………………………………………………………………………………………………………... Founder effect (when a small group breaks away from a larger population to colonise a new territory) 2. …………………………………………………………………………………………………………………………………………………... Compare the different types of selection Stabilising Selection Where an intermediate phenotype is favoured at the expense of both phenotypic extremes Effect: …………………………………………………………………………………………………………………………………………….. Human birth weights (too large = birthing complications / too small = risk of infant mortality) Example: ………………………………………………………………………………………………………………………………………… Directional Selection Where one phenotypic extreme is selected at the cost of the other phenotypic extreme Effect: …………………………………………………………………………………………………………………………………………….. Antibiotic resistance in bacteria (presence of antibiotic = ⬆ resistance) Example: ………………………………………………………………………………………………………………………………………… Disruptive Selection Where both phenotypic extremes are favoured at the expense of the intermediate phenotypes Effect: …………………………………………………………………………………………………………………………………………….. Pigmentation of peppered moth (dark or light coloration for camouflage) Example: ………………………………………………………………………………………………………………………………………… Speciation Discuss the different types of reproductive isolation Temporal Description Example Temporal isolation occurs when two …………………………………………………………… Leopard frogs and wood frogs reach …………………………………………………………… populations differ in their periods of …………………………………………………………… sexual maturity at different times in …………………………………………………………… activity or reproductive cycles …………………………………………………………… the spring and hence cannot interbreed …………………………………………………………… …………………………………………………………… …………………………………………………………… Behavioural isolation occurs when two …………………………………………………………… Certain populations of crickets may be …………………………………………………………… populations exhibit different specific Behavioural Geographic …………………………………………………………… courtship patterns morphologically identical but only …………………………………………………………… respond to specific mating songs …………………………………………………………… …………………………………………………………… …………………………………………………………… …………………………………………………………… Geographic isolation occurs when two …………………………………………………………… …………………………………………………………… populations occupy different habitats or …………………………………………………………… …………………………………………………………… separate niches within a common region …………………………………………………………… …………………………………………………………… …………………………………………………………… …………………………………………………………… Lions and tigers occupy different habitats and do not interbreed (usually) Define speciation Speciation is an evolutionary process that results in the formation of new species from pre-existing species ………………………………………………………………………………………………………………………………………………….......... It occurs when reproductive isolating mechanisms prevent two organisms from producing fertile offspring ………………………………………………………………………………………………………………………………………………….......... Distinguish between allopatric and sympatric speciation Allopatric Allopatric speciation occurs when a geographical barrier physically isolates populations of an ancestral species ………………………………………………………………………………………………………………………………………………….......... The two populations begin to genetically diverge until they can no longer interbreed (speciation) ………………………………………………………………………………………………………………………………………………….......... Sympatric Sympatric speciation is divergence of species within the same geographical location (no physical barrier) ………………………………………………………………………………………………………………………………………………….......... Reproductive isolation may be a result of genetic abnormalities (e.g. chromosomal errors) ………………………………………………………………………………………………………………………………………………….......... Explain, with the aid of the diagram, how polyploidy can result in a speciation event Sympatric speciation is most commonly caused as the result of a meiotic failure during gamete formation ………………………………………………………………………………………………………………………………………………….......... If meiotic cells fail to undergo cytokinesis, chromosomal number will double in the gamete (diploid not haploid) ………………………………………………………………………………………………………………………………………………….......... This will result in offspring that have additional sets of chromosomes (polyploidy) ………………………………………………………………………………………………………………………………………………….......... Speciation will result if the polyploid offspring are fertile but cannot interbreed with the parent population ………………………………………………………………………………………………………………………………………………….......... It is more common in plant species that can self-fertilise and reproduce asexually (vegetative propagation) ………………………………………………………………………………………………………………………………………………….......... Distinguish between phyletic gradualism and punctuated equilibrium Phyletic gradualism Speciation occurs following continuous change at a constant pace over a long period of time ………………………………………………………………………………………………………………………………………………….......... Arises via a gradual accumulation of mutations (big changes result from many small changes) ………………………………………………………………………………………………………………………………………………….......... Punctuated equilibrium Speciation occurs rapidly in bursts with long periods of stability in between ………………………………………………………………………………………………………………………………………………….......... In stable periods, characteristics are maintained, but this is punctuated by periods of environmental change ………………………………………………………………………………………………………………………………………………….......... Compare divergent and convergent evolution Convergent Divergent Ancestral relatedness Species do not share common ancestry Species share a common ancestry Evolutionary effect Adopt similar phenotypic features due to shared selection pressures Adopt dissimilar phenotypic features due to different selection pressures Type of adaptation Analogous structures Homologous structures