Natural Selection
Define natural selection in one sentence and name the two necessary conditions for it to occur.
Natural selection: differential survival and reproduction of individuals with heritable traits suited to the environment. Two necessary conditions: heritable variation and differential reproductive success. Review this closely for accuracy, especially in math, as AI may have limitations.
What is speciation?
Speciation: process where one lineage splits into two or more genetically distinct species.
What is a phylogeny?
Phylogeny: evolutionary history and relationships among organisms, usually shown as a tree.
What does a cladogram show?
Cladogram: branching diagram showing relationships based on shared derived traits; not necessarily scaled to time
Name two types of evidence (fossil, anatomical, molecular, etc.) that support evolution.
Two types: fossil record and molecular (DNA/protein) evidence; also comparative anatomy, embryology, biogeography
Give an example (biological scenario) of directional selection and explain how allele frequencies change.
Example: Peppered moths in industrial England — dark morph increases when soot darkens trees (allele for dark coloration increases in frequency). Review this closely for accuracy, especially in math, as AI may have limitations.
Contrast allopatric and sympatric speciation with one brief example of each.
Allopatric: geographic isolation (e.g., river splits population). Sympatric: reproductive isolation without geographic separation (e.g., polyploidy in plants).
How do shared derived traits (synapomorphies) differ from shared ancestral traits (symplesiomorphies) in building phylogenies?
Synapomorphy: derived trait shared by a clade (e.g., feathers in birds). Symplesiomorphy: ancestral trait shared beyond the clade (e.g., backbone in vertebrates).
On a cladogram, what does a node represent?
A node represents a common ancestor where a lineage diverged (a branching point)
Explain how transitional fossils support the theory of evolution; give one specific example.
Transitional fossils show intermediate character states (e.g., Archaeopteryx with both reptile and bird traits)
Explain the difference between artificial selection and natural selection; include one classroom example for each.
Artificial selection: humans choose traits (e.g., dog breeding). Natural selection: environment selects (e.g., pesticide resistance evolves without human-designed breeding). Review this closely for accuracy, especially in math, as AI may have limitations.
Describe the role of reproductive isolation in speciation and give two types of reproductive isolating barriers.
Reproductive isolation prevents gene flow. Prezygotic: temporal, behavioral, mechanical, gametic. Postzygotic: hybrid inviability or sterility. Review this closely for accuracy, especially in math, as AI may have limitations.
Explain why molecular data (DNA sequences) often give more resolution than morphological data when reconstructing phylogenies.
Molecular data provide many independent characters (nucleotides) and often less subjectivity than morphological trait coding; helpful for recent divergences
Interpret this brief cladogram statement: “Species A and B share a more recent common ancestor with each other than either does with Species C.” What does that imply about branching order?
It implies A and B share a more recent common ancestor (their node is closer) than either shares with C; branching order places A and B as sister taxa
Describe genetic drift and explain how a population bottleneck differs from the founder effect.
Genetic drift: random allele frequency change. Bottleneck: large population reduced drastically → loss of alleles. Founder effect: small group colonizes new area → allele frequencies differ from source.
Describe how sexual selection differs from natural selection and give one real-world example.
Sexual selection: selection arising from mating success (e.g., peacock tail). Natural selection includes survival; sexual selection may reduce survival while increasing mating success. Review this closely for accuracy, especially in math, as AI may have limitations.
Explain how polyploidy can cause rapid speciation in plants; include why it works genetically.
Polyploidy doubles chromosome number; instant reproductive isolation from parent diploids because gametes incompatible — common in plants (e.g., wheat)
Describe horizontal gene transfer and explain one way it can complicate phylogenetic reconstruction.
Horizontal gene transfer (HGT): genes move between lineages (common in microbes), mixing signals and creating reticulate patterns rather than tidy bifurcating trees.
Describe how to root an unrooted cladogram and explain why rooting matters for evolutionary interpretation.
Rooting can be done using an outgroup (a lineage known to be outside the ingroup). Rooting gives directionality (ancestral → derived).
Explain the concept of adaptive radiation and describe one classic example (what triggered it and what diversified).
Adaptive radiation: rapid diversification into many niches often after new habitat or extinction event (e.g., Darwin’s finches after colonizing Galápagos)
Using Hardy-Weinberg as a baseline, list three assumptions of Hardy-Weinberg equilibrium and explain how violating each can lead to evolution by natural selection or other mechanisms.
Hardy-Weinberg assumptions: large population (no genetic drift), no migration, no mutation, random mating, no selection. Violations: small population → drift; migration → gene flow; selection → allele frequency change.
Outline a hypothetical sequence of events (population sizes, isolation, selection, genetic changes) that leads from one species to two distinct species over time.
Example sequence: large population → subpopulation isolated by barrier → different selection pressures and drift → accumulation of genetic differences → reproductive isolation evolves → speciation completed.
Given two competing phylogenetic trees for a group of organisms, name three lines of evidence you would use to evaluate which tree is better supported.
Evaluate trees using congruence with molecular data, fossil-calibrated divergence times, and statistical support measures (bootstrap/posterior probabilities), plus parsimony and likelihood scores
List and explain three common mistakes students make when reading cladograms (for each, show why it’s incorrect and what to look for instead).
Common mistakes: reading left-to-right as progress (incorrect: nodes, not tips, show relationships); assuming branch length = time without scale (incorrect unless labeled); treating similarity as always indicating close relationship (homoplasy/convergence can mislead).
Provide a concise explanation (including an equation or simple notation for allele frequency change) of how selection coefficient (s) affects changes in allele frequency for a beneficial allele in a large population under selection. Include assumptions.
Selection effect: approximate change in frequency of a beneficial allele each generation ≈ sp(1-p) for small s, where s is selection coefficient and p allele frequency; stronger s → faster increase