Lab Analysis
Learning Objectives
In this lesson, you will:
- Analyze data from evolution experiments and studies
- Interpret phylogenetic trees and cladograms
- Evaluate fossil record evidence
- Apply Hardy-Weinberg equilibrium concepts
Practice Quiz
Analyze these evolution lab scenarios. Click to reveal each answer.
Question 1: In a population, 84% of individuals show the dominant phenotype. If the population is in Hardy-Weinberg equilibrium, what is the frequency of the recessive allele?
Answer: If 84% dominant, then 16% are homozygous recessive (q2 = 0.16). So q = 0.4 (40% recessive allele frequency).
Explanation: Hardy-Weinberg: p2 + 2pq + q2 = 1. The recessive phenotype frequency (q2) gives us q. Here, sqrt(0.16) = 0.4.
Question 2: A cladogram shows a branch point between cats and dogs before a branch point between cats and lions. What does this tell you about relationships?
Answer: Cats and lions share a more recent common ancestor than cats and dogs. The more recent the branch point, the more closely related the organisms.
Explanation: Reading cladograms: count branch points between organisms. Fewer branches = closer relationship.
Question 3: Fossil layers show: bottom layer has trilobites only; middle layer has trilobites and simple fish; top layer has fish and amphibians. What pattern does this show?
Answer: Progression from simpler to more complex organisms over time. Older (deeper) layers have older organisms; newer layers show evolution of vertebrates.
Explanation: The fossil record shows organisms appearing in a sequence consistent with evolutionary predictions - fish before tetrapods, invertebrates before vertebrates.
Question 4: Scientists find that cytochrome c protein is identical in humans and chimps but differs by 13 amino acids between humans and moths. What does this suggest?
Answer: Humans and chimps are more closely related (recent common ancestor) than humans and moths (distant common ancestor). More differences = more evolutionary distance.
Explanation: Molecular biology provides evidence for evolution. Proteins accumulate differences over time; fewer differences indicate closer relationship.
Question 5: In an experiment, bacteria in two environments (with and without antibiotics) are compared after 100 generations. What results would support natural selection?
Answer: The antibiotic environment population should show higher frequency of resistance genes. Control population should maintain original frequencies.
Explanation: This tests directional selection. The selective pressure (antibiotic) should cause evolution; no pressure means no selection.
Question 6: What conditions must be met for a population to be in Hardy-Weinberg equilibrium?
Answer: 1) No mutation, 2) Random mating, 3) No selection, 4) Large population size (no drift), 5) No gene flow (no migration).
Explanation: These conditions are rarely met in nature. Hardy-Weinberg is a null hypothesis; deviations indicate evolution is occurring.
Question 7: A transitional fossil shows features of both fish (scales, fins) and amphibians (limb-like fins, lungs). Why is this significant?
Answer: Transitional fossils provide direct evidence of evolution between groups. Tiktaalik, for example, shows intermediate features between fish and tetrapods.
Explanation: These fossils demonstrate evolutionary transitions that theory predicts. They fill gaps in the fossil record.
Question 8: In a simulation, 1000 red and 1000 blue beads represent alleles. Each generation, 100 beads are randomly selected to "reproduce." What evolutionary process is being modeled?
Answer: Genetic drift. Random sampling of alleles, especially with small sample sizes, can cause allele frequency changes unrelated to fitness.
Explanation: With only 100 beads selected, by chance you might get 55 red and 45 blue, changing frequencies. This effect is stronger with smaller populations.
Question 9: An island has finches with beak depths normally distributed around 10mm. After a drought that killed plants with small seeds, surviving finches average 12mm beak depth. What type of selection occurred?
Answer: Directional selection. The mean shifted in one direction (toward larger beaks) because larger beaks were better for surviving large seeds.
Explanation: This is documented in the Galapagos finch studies by the Grants - observable evolution in response to environmental change.
Question 10: How would you design an experiment to test whether a trait is due to genetic inheritance or environmental factors?
Answer: Raise genetically similar organisms in different environments (tests environmental effects) AND raise genetically different organisms in the same environment (tests genetic effects). Compare trait expression.
Explanation: This tests nature vs. nurture. Common garden experiments and twin studies use this approach to separate genetic and environmental contributions.
Next Steps
- Practice reading phylogenetic trees
- Review Hardy-Weinberg calculations
- Move on to claim-evidence writing when ready