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General Biology: Evolution and Development Study Guide

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  • What are the three body axes in animal development?

    Anterior-posterior (head to tail), dorsal-ventral (back to belly), and left-right axes established by morphogen gradients.

  • What is pattern formation in embryonic development?

    The process by which cells acquire different identities based on their position using morphogen concentration gradients.

  • Define a morphogen and its role.

    A signaling molecule with a concentration gradient that determines cell fate; different concentrations specify different cell identities (e.g., Bicoid in Drosophila).

  • What is a regulatory cascade in gene expression?

    A sequence where one gene product activates or represses the next, amplifying initial signals into precise cell fates (e.g., Bicoid → gap genes → pair-rule genes → segment polarity genes → Hox genes).

  • What do homeotic (Hox) genes do?

    Specify the identity of body segments. Mutations can transform one segment into another. They are conserved and collinear (chromosome order matches body axis expression).

  • Explain heterometry, heterochrony, and heterotopy.

    Heterometry: change in amount of gene expression. Heterochrony: change in timing. Heterotopy: change in location of gene expression.

  • What is the key insight of Evo-Devo regarding gene expression and evolution?

    Same genes can produce different outcomes due to changes in gene regulation, driving evolutionary differences without altering gene sequences.

  • Difference between typological and population thinking in evolution?

    Typological: species are fixed ideal types, variation is noise. Population: variation within populations is real and important; populations evolve over time.

  • List the four postulates of natural selection.

    1) Variation exists. 2) Variation is heritable. 3) More offspring produced than survive. 4) Survival and reproduction are non-random.

  • What were Darwin's two major influences on his theory?

    1) Lyell's geology: Earth is ancient with slow changes. 2) Malthus: populations overproduce leading to competition and struggle for existence.

  • Difference between individual and population in evolution?

    Individual: target of selection (traits selected for/against). Population: unit of evolution (allele frequencies change over generations).

  • What is Hardy-Weinberg equilibrium (HWE)?

    A null model where allele frequencies remain constant if no evolution occurs; requires no selection, random mating, no mutation, no migration, and large population size.

  • How does inbreeding affect allele and genotype frequencies?

    Allele frequencies remain unchanged; genotype frequencies shift toward more homozygotes and fewer heterozygotes. Does not cause evolution directly but exposes recessive alleles to selection.

  • Describe the four modes of natural selection.

    Directional: favors one extreme, reduces variation.
    Stabilizing: favors intermediate, reduces variation.
    Disruptive: favors extremes, increases variation.
    Balancing: maintains multiple alleles, maintains/increases variation.

  • What is genetic drift and when is it most significant?

    Random changes in allele frequencies due to chance, most powerful in small populations, can fix or lose alleles randomly.

  • Compare founder effect and bottleneck effect.

    Founder effect: small group starts new population with subset of alleles.
    Bottleneck effect: population size drastically reduced, survivors carry random allele subset.
    Both reduce genetic variation.

  • How does gene flow influence populations?

    Movement of alleles between populations; homogenizes populations making them genetically similar; low gene flow allows divergence and speciation.

  • Why is mutation important for evolution?

    Mutation is the ultimate source of new genetic variation; without it, evolution would lack raw material for change.

  • How do you identify the most closely related taxa on a phylogenetic tree?

    Find the taxa that share the most recent common ancestor by tracing back to the deepest shared node; tip order does not indicate relatedness.

  • Define monophyletic, paraphyletic, and polyphyletic groups.

    Monophyletic: ancestor and all descendants (valid clade).
    Paraphyletic: ancestor and some descendants (invalid).
    Polyphyletic: taxa from different ancestors (invalid).

  • Difference between homologous and homoplastic characters?

    Homologous: similarity due to common ancestry.
    Homoplastic: similarity due to convergent evolution, misleading for trees.

  • What is the Biological Species Concept and its limitation?

    Species are groups that can interbreed and produce fertile offspring, reproductively isolated from others. Limitation: cannot apply to asexual organisms, fossils, or allopatric populations.

  • What is the order of events in allopatric speciation?

    1) Geographic barrier or colonization isolates populations.
    2) Genetic divergence via selection, drift, mutation.
    3) Reproductive isolation evolves as a result.

  • Contrast prezygotic and postzygotic isolation barriers.

    Prezygotic: prevent mating or fertilization (behavioral, temporal, mechanical).
    Postzygotic: reduce hybrid fitness after fertilization (sterility, inviability).

  • What happens during fusion and reinforcement at secondary contact?

    Fusion: insufficient divergence leads to populations merging.
    Reinforcement: low hybrid fitness strengthens prezygotic barriers, completing speciation.

  • What is a molecular clock and how is it calibrated?

    Estimates divergence times using DNA/protein mutation rates; calibrated with fossil record to anchor timing.

  • Define adaptive radiation with an example.

    Rapid diversification of one lineage into many ecological niches. Example: Darwin's finches in the Galápagos.

  • What is the Cambrian Explosion and its significance?

    ~541 million years ago, rapid appearance of most major animal phyla in fossil record; shows evolution can be rapid and complex body plans evolved.

  • Name two limitations of the fossil record.

    1) Incomplete preservation (soft-bodied organisms rarely fossilize).
    2) Biased toward hard-bodied organisms; gaps are absence of evidence, not evidence of absence.