Honors Bio Unit 3: Evolution

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48 Terms

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Evolution

The process of biological change in populations over time that makes descendants genetically different from their ancestors.

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Two types of evolution

Microevolution & Macroevolution

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Microevolution

Evolution can occur on a small scale affecting a single population

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Macroevolution

Evolution on a large scale affecting changes in species across a population

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Charles Darwin’s Theory

Natural Selection

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Natural Selection

Organisms with the “best” traits (adaptations) will live longer and reproduce more than others,
causing changes in the population over time by acting on traits that are heritable.

  • Survival of the Fittest

    • Fitness

  • Based on:

    • Overproduction of offspring

    • Variation

    • Adaptation

    • Descent with modification

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Fitness

A measure of how well you can survive in your environment and pass on your genes

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Overproduction of Offspring

Lots of offspring and limited resources causes competition for those resources

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Variation

Differences in the physical traits of organisms

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Sources of Variation

  • Random mutations = ultimate source

  • Genetic recombination

  • Migration (gene flow)

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Adaptation

A feature that allows an organism to better survive in its environment

  • Beneficial traits will become more common over time

    • Because organisms should live longer and thus be able to reproduce more

    • This changes the gene pool = combined alleles of all individuals in a population

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Gene pool

The combined alleles of all individuals in a population

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Descent with Modification

A change in gene frequency over time

  • Natural selection leads to populations with new phenotypes adapted to new situations

  • Their traits come from their ancestors

  • Beneficial traits should become more common over time

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Individuals do not evolve, populations do!

  • An individuals does not evolve, because their allele frequencies don’t change. Populations evolved because their allele frequencies change.

  • Individuals in a population can be subject to natural selection, but the individual itself cannot ‘evolve’ in the biological sense of the world. They can only contribute to the evolution of a population by affecting the allele frequencies in that population.

  • Analogy: Pixels do not play, videos do.

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3 Modes of Selection

  1. Directional Selection

  2. Disruptive Selection

  3. Stabilizing Selction

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<p>Directional Selection (Extreme) </p>

Directional Selection (Extreme)

Increases the expression of an extreme version of a trait in a population.

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<p>Disruptive Selection (2 groups)</p>

Disruptive Selection (2 groups)

A process that splits a population into 2 groups;
removes individuals with average traits and favors the two extremes

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<p>Stabilizing Selection (Average)</p>

Stabilizing Selection (Average)

Eliminates extreme expressions of a trait when the average expression leads to higher fitness.

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Allele Frequencies

Each allele has a frequency in a population’s gene pool

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Allele Frequency

# of times the allele appears in a population (how common it is)

  • The higher the frequency = the greater the allele is there
    (and the more common the trait is)

  • Shows how frequently the allele appears in the gene pool

    • Gene pool = the combined alleles of all individuals in a population

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p + q = 1

Formula for calculating frequencies

  • p = frequency of the dominant allele

  • q = frequency of the recessive allele

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5 Mechanisms of Microevolution

  1. Mutations

  2. Natural Selection

  3. Genetic Drift

  4. Gene Flow

  5. Non-random Mating (Sexual Selection)

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Mutations

Any change in the DNA sequence

  • Creates new genotypes and thus new phenotypes

    • Changes the allele frequency too

  • Increases variation

  • Can be harmful, beneficial, or neutral

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Genetic Drift

Random Change in the frequency of alleles in a population over time

  • Usually a sharp decrease in population size

  • Usually results in a loss of genetic variation

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Gene Flow

The movement of genes into/out of a population

  • Occurs during migration

  • Results in an increase in genetic variation

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Sexual Selection (Non-random Mating)

The selection of traits that aren’t necessarily good for survival fitness, but you can’t pass on your genes without them, because you can’t reproduce.

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Genetic Equilibrium (Hardy-Weinberg Equilibrium)

When there are NO changes in the allele frequencies in a population over time.

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Speciation

Forming of a new species by evolution from pre-existing species

  • Some sort of isolation must occur

  • Gene pools gradually become different and are no longer able to reproduce

    • The 2 groups are different species

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Species

Group of organisms that can successfully interbreed and produce viable, fertile offspring.

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Isolation

Separation of different population into smaller units,
to prevent interbreeding between distinct species

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Types of Isolation

  • Geographical

  • Temporal = timing

  • Behavioral

  • Ecological = different niches (roles in the ecosystem)

  • Reproductive

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Niche

Role in the ecosystem

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Extinction

Elimination of a species

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Gradual Extinction

Occurs at a slow rate
(eg. changes in climate, natural disasters)

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Mass Extinction

Occurs when a catastrophic event changes the environment suddenly
(eg. massive volcano, tsunami)

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Gradualism

Slow, constant changes over a long period of time.

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Punctuated Equilibrium

Bursts of change → periods of stability

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<p>Divergent Evolution</p>

Divergent Evolution

A number of different species arise from one common ancestor

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Adaptive Radiation

A type of divergent evolution occuring on a small scale over a shorter period of time

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<p>Convergent Evolution</p>

Convergent Evolution

When unrelated species evolve similar characteristics because they live in similar environments

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Coevolution

Occurs when two populations of organisms form a specialized relationship and thus change in response to each other
(eg. flowers and the insects that pollinate them)

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Taxonomy

Field of biology that classifies organisms

  • Organizes organisms by similar characteristics

  • Divided into 3 domains

    • Eubacteria = prokaryotes (“true bacteria”, like pathogens)

    • Archaebacteria = prokaryotes in extreme environments

    • Eukarya = eukaryotes

  • Then further subdivided

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Bionomial nomenclature

2-name naming system

  • Genus species

    • Always in italics

    • First capitalized, second not

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Phylogeny

Evolutionary history of a species

  • Works to piece together evolutionary history of relatedness based on shared inherited characteristics

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Phylogenetic tree

A diagram used to predict evolutionary relationships among groups of organisms

  • Branch points show a news species diverging from the common ancestor

  • Classifies organisms into major taxa (groups) based on evolutionary relationships

  • Classifies groups of species in the order in which they descended from a common ancestor using homologous features

    • Any heritable traits (DNA, proteins, anatomical structures, etc.) that are the result of divergent evolution

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Maximum Parsimony

Use the simplest explanation for creating the tree

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What can we learn from a phylogenetic tree?

  • Which groups are most closely related

  • Which groups are least closely related

  • Which group diverged first (longest ago).

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<p>Reading Phylogenetic Trees </p>

Reading Phylogenetic Trees

  • Start from the “root” = common ancestor

    • As you move away from the root, you move forward in time

  • Speciation = branching of a family tree

  • Extinction = loss of one of the branches

  • Each node represents a more recent common ancestor.