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UBC Bio 121-Evolution review.doc

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BIOL 121
James( Jim) Cooke

UBC Bio 121: Evolution-James Cooke Lena C Definition: Evolution- Change in genetic characteristics-allele frequencies over time via natural selection * Individuals do not evolve, selection acts on individuals;population is evolving when ratio of genetic type is changing Natural Selection- individuals with certain heritable traits tend to produce more offspring than individuals without that trait, leads to change in genetic makeup. * Natural Selection has 4 postulates: 1. Variation in population-Individual organisms that make up a population must vary in traits they posses, ex: size & shape 2. Heritable variation-Some traits are heritable 3. Selection-In every generation more offspring are produced than survived;only some individuals in the population survive long enough to produce offspring 4. Differential survival or reproduction- survival and reproduction are not random; those with favorable variations survive an go on to reproduce * Natural selection is not goal directed or progressive. It simply favors individuals better adapted to the environment at the time * Natural selection does not require competition, just a fitness difference *Selection does not equal evolution; evolution is an outcome of the process of natural selection Population- collection of individuals in a group Darwinian Fitness- ability to produce more offspring, relative to that ability in other individuals in a population * Darwin referred to successful individuals as "more fit" than other individuals Ex: Self sacrificing alleles: individuals with this alleles do not produce offspring.As a result, selfish alleles increase frequency while self-sacrificing alleles decrease in frequency, therefore it is not possible for individuals to sacrifice based on choice for the good of the species. Adaptation- increases individual's ability to create offspring; heritable trait that increases the fitness of an individual in a particular environment than other individuals lacking the trait Acclimation- changes in an individuals phenotype that occur in response to changes in environmental conditions Vestigial trait- structures with no function; ex: human tail bone Genetic Correlation- genetic constraint; lack of genetic variation;selection on one trait causes change in another trait.Occur because of pleitropy-single gene affect more than one trait Fitness Trade-off- compromise between traits; Balancing selection or heterozygote advantage- heterozygous individuals increase fitness than homozygous= genetic variation maintained in population Genetic variation- # and relative frequency of alleles that are present in a particular population *low genetic variation= bad for population when environment changes effects population Directional selection- one extreme phenotype have higher fitness than the average or other extreme=reduce genetic variation over time Disruptive selection- only extreme phenotype on either range of variation have higher fitness=genetic variation overtime Stabilizing selection- only average phenotype have higher fitness=no genetic variation over time Genetic drift-any change in allele frequencies due to random events; causes allele frequencies to change randomly. May cause increase or decrease fitness;drift up or down. May cause loss or fixation of alleles (0=loss, 1=fix). Most pronounced in small population Genetic bottleneck-sudden reduction of the # of alleles in a population=change in allel frequencies Founder Effect- change in allele frequencies that often occurs when a new population is established from a small group of individuals due to sampling error Gene flow- movement of alleles between populations; when individuals of one population leaves and joins another then breed.Allele frequencies may change from new alleles from immigrated population and the other remove alleles from their old populations Mutation-introduce new alleles, can be advantageous or detrimental Inbreeding-mating between relatives; mating wit closely related individuals Sexual Selection-occurs when individuals within a population differ in their ability to attract mates; females invest more in their offspring than males Asymmetry of sex-1. Eggs are large and consume large energy, females produce few young over course of lifetime. Female fitness is limited primarily by ability to gain resources to produce more eggs. 2. Men can have limitless # of offspring, male fitness limited to # females it can mate with Sexual Dimorphism- any trait that differs between males and females; ex: antlers on deer=male Intersexual fitness- competition between male and female on how they look Intrasexual fitness- competition within species for reproduction & resources;male vs male Hardy-Weinberg principle-describe the allele frequencies in a population; gene pool combine at random; a null hypothesis: what happens when evolutionary mechanisms are not operating Biological Species Concept-reproductive isolation between populations;advantage: isolation=evolutionary independence; disadvantage: does not apply to fossils & asexual species Mechanisms of reproductive isolation: Prezygotic isolation- before fertilization: Temporal- isolated b/c breeding at different times Habitat- isolated b/c breed at different habitat Behavioral-population do not interbreed b/c courtship displays differ Mechanical-male and female genitalia are incompatible Postzygotic isolation-reproduction isolation resulting from mechanism that operate after mating of individuals of two different species occurs Hybrid viability-hybrid offspring do not develop normally & die as embryo Hybrid sterility- hybrid offspring mature but are sterile adults Morphospecies Concept-morphologically distinct populations; identify evolutionary independent lineages by difference in size, shape or other morphological features; advantage: widely applicable; disadvantage: subjective in research Phylogenetic Concept- smallest monophyletic group on phylogentic tree; based upon share in common ancestor; advantage: widely applicable; disadvantage: very few well- estimated phylogenis available Phylogeny-evolutionary history of a group of organism Phylogenetic tree- show ancestor-descendant relationship among populations or species, clarifies who is related to whom Branch-a population through time Node/fork- the point where 2 branches diverge; when ancestral groups split into 2 or more descendant groups Tip (terminal node)-end point of a branch, represents group Cladistic approach- based statist
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