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129 Cards in this Set
- Front
- Back
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Vestigial traits
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Reduced or incompletely developed traits that were present in a common ancestor
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gradualism
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gradual geological changes
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Uniformitarianism
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steady change can result in big differences
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Homology
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Similarity in form through common descent
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developmental homology
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similarity through common developmental pathways
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genetic homology
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Similarity in the Genetic Code
ex: Eye location in human and fruit fly influenced by same gene |
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Natural Selection
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the process by which better adapted organisms are more likely to survive and become the parents of the next generation
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Adaptations
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evolutionary modifications that improve the chances of survival and reproductive success
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Over-production
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Many more individuals are born in each generation than will survive to reproduce
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Variation
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variation within populations
ex: dog breeds |
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Differential Reproductive Success
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individuals with certain traits have a better chance of surviving and reproducing than others with slightly different traits
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Heritability
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Some of the traits resulting in differential survivorship and reproduction can be passed from one generation to the next
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Time
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Changes have occurred over vast periods of time
Measured in generations |
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what are darwins 5 observations
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time, heritability, differential reproductive success, variation and over production
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Adaptation
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a trait that that has formed through differential survival and reproduction – natural selection.
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Darwinian Fitness
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the ability to pass genes from one generation to the next
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common ancestry
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All existing organisms are modified descendants of other organisms
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Historical constraints
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all traits evolve from preexisting traits
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pleiotropy
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single allele affects multiple traits
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phenotypic variation
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changes in traits from one generation to the next
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genotypic variation
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changes in allele frequency from one generation to the next
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species
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a group of populations with the ability to interbreed
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population
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a localized group of individuals in the same species
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gene pool
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the aggregate of genes in a population
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diploid organisms
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have two alleles for each gene locus
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homozygote genotypes
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both alleles same
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Heterozygotes genotypes
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two different alleles
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Allele frequency
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the relative frequency (proportion) of an allele in a population
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is the hardy-weinberg equation being in equillibrium a sign of evolution?
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no, if its in equilibrium, then evolution is not occuring
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what are the five conditions of the hw theory?
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Random Mating
No mutation Large population size – no genetic drift No migration – no gene flow No natural selection |
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What is adaptive evolution?
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change in a population as a result of natural selection that in turn, results in the offspring’s ability to pass on a greater proportion of their genes
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nonadaptive evolution ?
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nonadaptive evolution does not affect the offspring’s ability to pass on genes to the next generation
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inbreeding
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mating between closely related individuals
causes accumulation of deleterious alleles inbreeding depression |
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assortative mating
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mating between individuals of similar phenotypes
increases homozygosity |
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Mutation
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a direct change in the DNA sequence of the germ cells
ultimate source for genetic variation |
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Genetic Drift
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smaller populations are more likely to experience changes in allele frequencies due to drift
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bottleneck effects
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disasters reduce population size resulting in a non-representative sampling of the original gene pool
- reduces genetic variability |
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founder effects
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colonization of a new habitat by a few or single individual from the parent population resulting in a decrease in genetic variation
e.g. Hawaiian “picture-winged” Drosophila |
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Gene Flow
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genetic exchange of fertile individuals between populations
ex:Frequency of black and white peppered moths |
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what Three ways can natural selection alter the frequency of heritable traits.
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1) stabilizing selection
2) directional selection 3) disruptive selection |
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Directional Selection
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extreme forms at either end of the distribution have higher fitness
average shifts to the left or the right while the variance does not change ex:human height, beak width in Galapagos finches |
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Disruptive Selection
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variants at both ends of the distribution have higher fitness than intermediate forms
no change in the average but increases the variance rare can result in new species Rhagoletis flies, black-bellied seed cracker |
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founder effects
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colonization of a new habitat by a few or single individual from the parent population resulting in a decrease in genetic variation
e.g. Hawaiian “picture-winged” Drosophila |
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runaway selection
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exaggerated traits through a positive feedback loop with female choice for males with extreme traits
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Sexual Selection
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A subset of Natural selection in which traits are exclusively related to reproduction
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phenotypic plasticity
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the phenotype depends on the environment in which the organism is raised
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Discrete traits
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categorical in nature
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Quantitative or continuous traits
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continuous variation in trait
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epistasis
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multiple loci acting on a single trait
e.g. height, color patterns |
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Mutation
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ultimate source of genetic variation
only mutations in the germ line can be inherited |
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Recombination
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most important source of variation
the unique combining of different alleles during meiosis |
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Diploidy
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hides genetic variation as recessive alleles
the rarer the allele - the greater the protection |
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hybrid vigor
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crossbreeding between varieties that produces more successful offspring
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heterozygote advantage
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heterozygote has a greater fitness than either homozygote
sickle-cell anemia |
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Polymorphism
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discrete variation that results in two or more forms within a population
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Frequency-dependent selection
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the reproductive success of one morph declines if it becomes to common
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Clinal Variation
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gradual geographical variation in a species’ phenotype
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gradient variation
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spatial or temporal environmental variation
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Heterozygote advantage
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heterozygotes have higher fitness – maintains genetic variation because neither allele has higher fitness
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Codominacne
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heterozygote phenotype affected by both alleles
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Recombination
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most important source of variation
the unique combining of different alleles during meiosis |
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hybrid vigor
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crossbreeding between varieties that produces more successful offspring
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heterozygote advantage
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heterozygote has a greater fitness than either homozygote
sickle-cell anemia |
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Is all variation adaptive?
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Neutral genetic and phenotypic variation is abundant and clearly not all of it is adaptive
e.g. neutral allele – does not affect fitness allele variation in human hemoglobin e.g. human chin e.g. human finger prints |
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historical constraints
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evolution uses existing structures and genes, modifies them to better solutions
selection can only act on existing variation |
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evolutionary compromises or tradeoffs
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The connection between genotype and phenotype can be ambiguous
e.g. pleitropy - a single gene that effects many traits sickle-cell gene |
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allometric growth
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difference of relative rates of growth for different parts of the body
human head - negative |
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Heterochrony
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changes in the rates of developmental timing
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paedomorphosis
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speciation that has resulted from the retention of larval characteristics relative to the parent species
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progenesis
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development that results in adults with larval phenotypes
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Homeosis
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alterations in the placement of different body parts
spatial displacement – additional segments in segmented organisms Modular bauplans |
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Conspecifics
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members of a species
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Anagenesis
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phyletic evolution - transformation of one species into another
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Cladogenesis
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branching evolution - building of one or more species from an ancestral (parent) species
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allopatric speciation
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geographic barriers isolate populations and function as barriers to gene flow
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Vicariance
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the splitting of populations by geologic events
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Dispersal
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the movement of individuals into new novel habitats
Some times referred to a parapatric speciation Founder effects |
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sympatric speciation
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Separation of the populations is not a physical barrier, but differences in environmental conditions or behavior
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disruptive selection
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The role of natural selection is stronger then the effect of gene flow maintaining reproductive isolation
ex:Heavy metal tolerance in plant species |
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Reproductive Barriers
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Mechanisms that prevent reproduction between individuals of closely related populations
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Prezygotic Barriers
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prevent the fertilization and the formation of a zygote
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spatial/habitat isolation
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individuals that live in different places in the environment
E.g. Rhagoletes flies – hawthorns and apples Incipient species |
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Temporal isolation
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breeding at different times of the year
e.g. eastern and western spotted skunk |
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behavioral isolation
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differences in behavior prevent matings
e.g. many closely related bird species |
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mechanical isolation
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anatomical incompatibility
e.g. hemipenes of closely related snake species |
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gametic isolation
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failure to form a zygote
e.g. many aquatic species with external fertilization |
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Postzygotic Mechanisms
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prevent the zygote from developing into a fertile adult
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hybrid zygote abnormality
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developing zygote dies due to genetic incompatibility
e.g. Rana (frogs) |
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hybrid sterility
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- hybrid offspring are not fertile
e.g. mule |
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hybrid breakdown
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- F1 hybrids are fertile, but F2 are not
e.g. cotton species |
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what are PREzygotic reproduction barriers?
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gemetic isolation,spatial/habitat isolation ,Temporal isolation ,behavioral isolation,mechanical isolation
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what are POSTzygotic reproduction barriers?
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hybrid zygote abnormality,hybrid sterility,hybrid breakdown,
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Secondary Species Contact
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Two previously separated populations once again come into contact
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how do we know if speciation occurs after Secondary Species Contact
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if interbreeding is unable to occur
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Introgression
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the spread of genes from one species to another via hybridization
- particularly in plants where new lines can reproduce asexually Aspidoscelis |
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Evolutionary Radiations
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Rapid divergent evolution within a lineage in a relatively short time.
ex:13 species of Darwin’s finches in the Galapagos Islands. |
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gradualism
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evolutionary change occurs at a constant and steady pace
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punctuated equilibrium
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evolution is episodic characterized by burst of rapid change and long periods of stasis
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Phylogenetics
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Reconstructing the evolutionary history of a lineage and showing ancestor-descendant relationships in a tree
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Cladistics
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taxa grouped based on synapomorphies (shared-derived characters)
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Phenetics
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taxa grouped based on measured similarities and differences (without taking into consideration homology)
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Ancestral
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features that were present in the ancestors of the group
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Derived
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features that arose within the group under study
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pleisomorphies
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Ancestral characters
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apomorphies
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Derived characters
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synapomorphies
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Shared-derived characters
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Parsimony
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most likely explanation is one that implies the least amount of change
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Evolutionary reversal
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reverting back to the ancestral condition
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Outgroup
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members of a closely related group that are not within the group of interest
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homoplasy
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similarity in function due to
convergent evolution and parallel evolution |
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convergent evolution
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independent evolutionary events that have led to similar phenotypes
ex:Flight in insects, mammals and birds |
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parallel evolution
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similar developmental processes in distantly related taxa
*Results in traits that do not reflect the evolutionary history – thus uninformative* |
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monophyletic group
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contains an ancestor and all of its descendants
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paraphyletic group
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a group that does not contain all descendants of an ancestor
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polyphyletic group
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a group that has more than one ancestor
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Substitution
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replacement of nucleotide base
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Synonymous or silent substitution
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no effect on phenotype
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Non-synonymous substitution
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changes AA sequence
Most are deleterious |
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Neutral Theory
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most mutations are selectively neutral – genetic drift important
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DNA-DNA hybridization
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similarity determined through annealing properties
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Restriction mapping
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similarity based on DNA fragment size
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DNA sequencing
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direct comparison of the genetic code
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Gene families
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a group of genes with related function
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Gene duplication
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from part of gene to entire genome
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Orthologs
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a single gene passed on through a common ancestor
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Paralogs
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related through duplication
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petrification
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minerals in the groundwater seep into tissue
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fossils that retain organic material
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amber, freezing, mummification
- potential to provide DNA |
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trace fossils
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foot prints, burrows, leaf impressions
- can infer behavior and ecology |
