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Exam 1 LT
Biodiversity Spring 2026
| Question | Answer |
|---|---|
| Identify Darwin and Wallace's contribution to the theory of evolution | Charles Darwin and Alfred Russel Wallace independently developed the idea of natural selection Their key contribution was identifying the mechanism that explains how evolution happens |
| Place Darwin and Wallace's theories in context of ideas proposed previously | Jean-Baptiste Lamarck (early 1800s) suggested that organisms change in response to their environment and pass on acquired traits While his mechanism was incorrect, Lamarck was the first to argue that species change over time and can go extinct |
| What are the five lines of evolution supporting evolution | Fossil record Biogeography Convergent evolution Direct observation (natural and artificial selection) Homologies |
| Describe the mechanism of natural selection | The process by which populations evolve because individuals with certain inherited traits survive and reproduce more successfully than others. Three main steps: variation, overproduction and competition, and differential reproductive success |
| Define descent with modification | Means that: All species are descended from common ancestors, Populations change over generations, and Descendant species are similar to their ancestors explains what happens over time: populations gradually change, and all species share common ancestor |
| Define homology | Fundamental similarity due to descent from a common ancestor |
| Define fossil | Traces of past organisms, usually preserved in sedimentary rock |
| Define homologous structure | body structure in different species that is fundamentally similar because it was inherited from a common ancestor, even if the structure now serves different functions |
| Define analogous structure | structure that is similar in function but not in evolutionary origin. These structures arise through convergent evolution, not shared ancestry |
| Define convergent evolution | 2 species from different lineages show similar characteristics because they occupy similar environments |
| Define vestigial structure | A spatial record of evolution |
| Define evolutionary tree | diagram that represents evolutionary relationships among organisms, showing how species are related through common ancestry and descent with modification |
| Define biogeography | study of the geographic distribution of species, both past and present, and provides a spatial record of evolution |
| Define artificial selection | process by which humans selectively breed organisms for desired traits, causing evolutionary change over generations |
| Define adaptation | heritable trait that increases an organism’s survival and reproductive success in a particular environment, produced by natural selection over time |
| What did Darwin/Wallace propose in the findings? | They proposed that: Individuals in a population vary, Many of those traits are heritable, More offspring are produced than can survive (resources are limited), Individuals with advantageous traits have higher reproductive success |
| According to Darwin and Wallace what happens over time regarding natural selection? | Over time, this leads to adaptations and descent with modification—populations gradually change across generations, and new species can arise |
| How did Darwin and Wallace build on Lamarck's ideas? | Darwin and Wallace improved on these earlier ideas by: Rejecting inheritance of acquired characteristics Providing a testable mechanism (natural selection) Supporting their theory with multiple independent lines of evidence |
| What is "Fossil record" related to evolution? What does it show? | Fossils are preserved remains or traces of ancient organisms. Their positions in rock layers help indicate relative age. Although incomplete, the fossil record shows: Gradual change over time, Transitional forms between ancestral and descendant species |
| What is "Biogeography" related to evolution? What are key patterns? | Biogeography is the geographic distribution of species. Key patterns: Isolated islands and continents have many endemic species, Closely related species appear in nearby regions, Similar fossils on distant continents suggest past land connections |
| What is "Convergent evolution" related to evolution? What does this show? | Convergent evolution occurs when unrelated species evolve similar traits because they live in similar environments that are analogous Shows: natural selection independently shapes organisms in comparable ways when they face similar environments |
| What is "Natural Selection" related to evolution? What is an example and what did the example show? | Observations in real time (i.e. Galapagos finches) This directly demonstrates evolution occurring within populations |
| What is "Artificial Selection" related to evolution? What are examples? What does selective breeding show? | Humans Humans deliberately breed organisms for desired traits (e.g., dogs, crops) Selective breeding shows that: Large changes can occur over relatively short time spans, Genetic variation already present in populations allows these changes |
| What is "Homologies" related to evolution? What are the three types? | similarity due to shared ancestry Anatomical, developmental, and molecular |
| What is anatomical homology? | Same basic structures (like forelimb bones) modified for different functions. |
| What is developmental homology? | Different species resemble each other during embryonic stages (e.g., human embryos show gill ridges and tails), indicating common ancestry. |
| What is molecular homology? | All life uses DNA. Closely related species have more similar DNA sequences than distant relatives. |
| Explain how the smallest unit of evolution is a population | Evolution is a change in allele frequencies over time Individual organisms do not evolve during their lifetimes; instead, populations evolve across generations as the frequencies of alleles in gene pools change |
| Explain why variation in populations is common | Most genes are polymorphic (have two or more alleles) Mutations introduce new alleles Sexual reproduction reshuffles alleles through recombination Gene flow introduces alleles from other populations |
| Explain why variation is necessary for natural selection | Selection can only act on heritable differences among individuals. Without variation, all individuals would have equal fitness, and no trait would be favored or eliminated |
| What is the Hardy-Weinberg equilibrium equation for allele frequency? What does each variable represent? | p + q = 1 p = frequency of dominant allele q = frequency of recessive allele |
| What is the Hardy-Weinberg equilibrium equation for genotype frequency? What does each variable represent? | p^2 + 2pq + q^2 = 1 p² = homozygous dominant 2pq = heterozygous q² = homozygous recessive |
| Describe the five conditions required for Hardy-Weinberg equilibrium | No mutations No natural selection Very large population size (no genetic drift) No migration (no gene flow) Random mating |
| Do populations have to meet all the conditions to remain in Hardy-Weinberg equilibrium? What do real populations do? What happens because of this? | Yes Real populations violate at least one of these conditions, allele and genotype frequencies usually change over time, meaning evolution occurs |
| What are the four patterns of natural selection? | Directional selection Stabilizing selection Disruptive selection Balancing selection |
| What is directional selection? What is an example? | Favors one extreme phenotype Antibiotic resistance |
| What is stabilizing selection? What is an example? | Favors intermediate phenotypes and selects against extremes Bird clutch size |
| What is disruptive selection? | Favors two or more extreme phenotypes over intermediates |
| What is balancing selection? | Maintains multiple alleles in a population including heterozygote advantage and frequency-dependent selection |
| What is an example of heterozygote advantage? | Sickle cell trait and malaria resistance |
| What is frequency-dependent selection? | Rare phenotypes have higher fitness |
| Define sexual selection | Form of natural selection that favors traits increasing mating success |
| What are the two types of sexual selection? Explain the difference | Intrasexual selection: Competition between members of the same sex (e.g., male-male combat) Intersexual selection: Mate choice by one sex, typically females choosing males with certain traits (e.g., elaborate displays) |
| Is natural selection goal-oriented? What is acted on? Why do traits persist? | No, acts only on existing variation Produces organisms that are “good enough”, not perfect Traits persist because they increase fitness in a specific environment, not because they are optimal or intentional. |
| Explain why genetic drift has a greater effect in small populations | Genetic drift is the random change in allele frequencies due to chance, not fitness. It has a greater effect in small populations because random events can dramatically alter allele frequencies |
| What are two situations where genetic drift occurs? Define them | Bottleneck effect: Population size is drastically reduced by chance events Founder effect: A small group establishes a new population with different allele frequencies |
| Define gene pool | All alleles for all genes in a population |
| Define population | Members of the same species living in the same area |
| Define microevolution | Small-scale changes in allele frequencies within populations |
| Define macroevolution | Large-scale evolutionary changes that produce new species or groups |
| Define bottleneck effect | Loss of genetic variation after a dramatic population reduction |
| Define founder effect | Reduced genetic variation when a new population is founded by few individuals |
| Define genetic drift | Random changes in allele frequencies due to chance |
| Define gene flow | Movement of alleles between populations |
| Define migration | Physical movement of individuals between populations |
| Define fitness | An individual’s reproductive success and contribution to the next generation’s gene pool |
| Define species based on the biological species concept. Describe limitations of this perspective. | Defines a species as a group of organisms that can interbreed in nature and produce viable, fertile offspring Limitations: Cannot be applied to asexual organisms Difficult or impossible to test in fossils Some species can hybridize occasionally |
| Define species based on the morphological species concept. Describe limitations of this perspective. | Defines species based on physical characteristics Limitations: Subjective (depends on observer) Morphologically similar species may be genetically distinct Phenotypic variation within a species can be misleading |
| Define species based on the ecological species concept. Describe limitations of this perspective. | Defines species based on ecological niche (habitat, resources, role) Limitations: Different species can occupy similar niches Difficult to apply broadly |
| Define species based on the phylogenetic species concept. Describe limitations of this perspective. | Defines species as the smallest monophyletic group on a phylogenetic tree Limitations: Requires extensive genetic data No clear cutoff for genetic difference |
| Why is reproductive isolation is necessary for divergence? | Reproductive isolation prevents gene flow between populations. Without gene flow, populations can accumulate genetic differences through mutation, natural selection, and genetic drift. Over time, this divergence can lead to speciation |
| What are the eight mechanisms of reproductive isolation? What are there categories? | Prezygotic barriers: Habitat isolation, Temporal isolation, Behavioral isolation, Mechanical isolation, and Gametic isolation Postzygotic barriers: Hybrid inviability, Hybrid sterility, and Hybrid breakdown |
| Common ways sympatric speciation occurs | Sympatric speciation occurs without geographic separation and commonly involves: Habitat differentiation within the same area Polyploidy (especially in plants) Sexual selection leading to assortative mating |
| Why is allopatric speciation is most common? | Allopatric speciation occurs when populations are geographically separated, completely interrupting gene flow. This allows genetic differences to accumulate independently, making it the most prevalent mechanism of speciation. |
| Define speciation | Formation of new species |
| Define reproductive isolation | Barriers preventing gene flow |
| Define fusion | Reproductive barriers weaken and populations merge |
| Define biological species concept | Species defined by ability to interbreed |
| Define allopatric speciation | Speciation via geographic isolation |
| Define sympatric speciation | Speciation without geographic isolation |
| Hybrid zone | Region where two species interbreed |
| Define polyploidy | More than two sets of chromosomes |
| Define hybrid | Offspring of two different species |
| Define intraspecific | Within a species |
| Define Interspecific | Between species |
| Define adaptive radiation | Rapid diversification into many species |
| How did the evolution of eukaryotic cells happen? What is the evidence? | Eukaryotic cells evolved via endosymbiosis, where ancestral prokaryotes engulfed other bacteria that became mitochondria and chloroplasts, supported by: Double membranes, Circular DNA, and Independent replication |
| Biases of the fossil record: what is the fossil record biased towards | The fossil record is biased toward: Organisms with hard body parts Species that lived in aquatic environments Abundant and widespread species Soft-bodied, rare, or terrestrial organisms are underrepresented |
| What are the Main steps in the origin of life? What is the evidence | Formation of organic molecules Polymerization into macromolecules Formation of protocells Origin of self-replicating molecules (RNA world) Evidence includes laboratory experiments and geological data, though exact mechanisms remain speculative |
| When did the earth form (approximately)? | ~4.6 billion years ago |
| When did prokaryotes first appear (approximately)? | ~3.5-4 billion years ago |
| When did eukaryotes first appear (approximately)? | ~2 billion years ago |
| When did multicellular eukaryotes first appear (approximately)? | ~1.5 billion years ago |
| When did animals first appear (approximately)? | <1 billion years ago |
| When did land plants first appear (approximately)? | ~500 million years ago |
| When did humans first appear (approximately)? | ~200, 000 years ago |
| What are major environmental changes that have occurred? What has happened as a result of these changes? | Atmospheric oxygen increase, Climate shifts, Continental drift, and Mass extinctions These changes caused extinctions and opened ecological niches, promoting adaptive radiation. |
| What is radiometric dating? | Radiometric dating uses isotope half-lives to estimate absolute age |
| What does the depth of a fossil reveal? | Fossils deeper in sedimentary rock are older than those above (relative dating) |
| Where did the first living cells evolve from? What evidence is there to support this? | The first living cells evolved in oceans, supported by early marine fossils and chemical stability of water. |
| What does spatial expression of genes mean? What does it influence? | Genes expressed in different locations and timings during development influence: Body patterning, Limb formation, Organ placement |
| Relate early development and evolutionary relationships | Comparing embryos reveals shared developmental pathways, helping infer common ancestry and evolutionary relationships |
| Does spatial expression of genes cause any evolutionary differences? | Small changes in spatial expression of genes can produce major evolutionary differences. |
| Why evolution is not goal-oriented | Evolution does not plan or strive for perfection. It acts on existing variation and favors traits that improve reproductive success in current environments only. |
| Define protocells | Precursor cell-like structures |
| Define hydrothermal vents | Hot, mineral-rich ocean vents |
| Define alkaline vents | pH-gradient vents aiding organic synthesis |
| Dine rikozynes | RNA molecules with catalytic function |
| Define endosymbiont | Organism living inside another |
| Define Cambrian explosion | Rapid diversification of animals |
| Define unicellular | Single-celled |
| Define multicellular | Many-celled |
| Define prokaryote | Cell without nucleus |
| Define eukaryote | Cell with nucleus |
| Define adaptive radiation | Rapid diversification |
| Define Half-life | Time for half of a radioactive isotope to decay |
| Are phylogenetic trees final? | Phylogenetic trees are not final — they are hypotheses based on current data. As new evidence becomes available (especially genetic data), trees may be revised or redrawn. |
| What are reasons they may be revised? | New fossil discoveries Improved molecular data Better understanding of homology vs homoplasy |
| What is a monophyletic group? What is another name for it? | Includes a common ancestor and all of its descendants Clade |
| What is a polyphyletic group? | Includes a common ancestor but not all descendants |
| What is a paraphyletic group? | Includes species from different ancestors, grouped by superficial similarity (e.g., “warm-blooded animals”) |
| What type of group is preferred (monophyletic, polyphyletic, paraphyletic)? Why? | Monophyletic They accurately reflect evolutionary history and descent from a common ancestor |
| What does the principle of parsimony state? | The principle of parsimony states that the simplest explanation — the tree requiring the fewest evolutionary changes — is preferred. |
| Why is the simplest explanation preferred for phylogenetic? | Fewer trait changes = more likely tree Helps choose among multiple possible trees Core idea in cladistics |
| How do neutral mutations spread through populations? | Neutral mutations do not affect fitness. They can spread through populations by genetic drift rather than natural selection |
| What are the key points of neutral mutations? | Random changes in allele frequencies More likely to spread in small populations Accumulate steadily over time |
| What are neutral mutations the basis for? | Molecular clocks |
| What does a molecular clock use to determine when they diverged? | A molecular clock uses the number of DNA or protein differences between species to estimate how long ago they diverged. |
| What are the principles of a molecular clock? | More differences = more time since divergence Mutation rates are not perfectly constant Fossils are used to calibrate molecular clocks |
| What do fast-evolving genes show? What do slow-evolving genes show, related to molecular clocks? | Fast-evolving genes → recent divergences Slow-evolving genes → deep evolutionary history |
| What is horizontal gene transfer? | Movement of genes between unrelated organisms Common in prokaryotes Produces a “web of life”, not a simple tree |
| What is convergent evolution? | Similar traits evolve independently due to similar selection pressures Produces homoplasies Can make unrelated species appear closely related |
| What are the naming rules for a binomial nomenclature? | Two-part scientific name: Genus + species Genus capitalized, species lowercase Both italicized (or underlined) |
| What do convergent evolution and horizontal gene transfer do with tree construction? How? | Both processes complicate tree construction by obscuring true ancestry |
| What is the taxonomic hierarchy (broad → specific)? | Domain Kingdom Phylum Class Order Family Genus Species |
| What is each level of the taxonomic hierarchy called? | Each level is called a taxon |
| Define phylogeny | evolutionary history of a species |
| Define systematics | study of biological diversity and evolutionary relationships |
| Define taxon | any named taxonomic group |
| Define sister taxa | two lineages sharing an immediate common ancestor |
| Define analogy | similarity due to convergent evolution |
| Define homology | similarity due to shared ancestry |
| Define clade | monophyletic group |
| Define monophyletic | ancestor + all descendants |
| Define paraphletic | ancestor + some descendants |
| Define polyphyletic | groups from different ancestors |
| Define shared ancestral character | trait present before the most recent common ancestor |
| Define shared derived character | trait that evolved in the most recent common ancestor |
| Define homoplasy | similarity not due to common ancestry (often from convergence) |
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