AP Bio Unit 7 Progress Check FRQ: A Complete Guide to Mastering the Free‑Response Question
The AP Biology Unit 7 Progress Check FRQ focuses on evolution, natural selection, and the mechanisms that drive biodiversity. Understanding how to approach this free‑response question is essential for earning a high score on the exam and demonstrating mastery of concepts such as Hardy‑Weinberg equilibrium, speciation, phylogenetic trees, and genetic drift. This article breaks down the structure of the Unit 7 Progress Check FRQ, provides a sample prompt with a model answer, explains the scoring rubric, and offers proven study strategies to help you tackle the question with confidence.
Understanding AP Biology Unit 7
Unit 7 of the AP Biology curriculum is titled “Evolution.” It builds on the molecular and cellular foundations covered in earlier units and connects them to the large‑scale patterns of life. Key topics include:
- Natural selection – differential survival and reproduction based on heritable traits.
- Evidence for evolution – fossil record, comparative anatomy, embryology, molecular biology.
- Mechanisms of evolution – mutation, gene flow, genetic drift, non‑random mating.
- Hardy‑Weinberg principle – mathematical model for predicting allele frequencies in a non‑evolving population.
- Speciation – allopatric, sympatric, and polyploid pathways; reproductive isolating mechanisms.
- Phylogenetics – constructing and interpreting cladograms and phylogenetic trees.
- Macroevolution – adaptive radiation, convergent evolution, extinction events.
About the Pr —ogress Check FRQ is designed to assess your ability to integrate these concepts, analyze data, and construct logical explanations—skills that are directly tested on the AP exam No workaround needed..
Typical Structure of the Unit 7 Progress Check FRQ
College Board’s Progress Check FRQs follow a consistent format that mirrors the actual exam:
- Prompt Presentation – A short scenario, data set, or diagram is provided (e.g., a table of allele frequencies, a phylogenetic tree, or a description of a population undergoing selection).
- Multiple Parts – The question is divided into 3–5 sub‑questions (labeled (a), (b), (c), …). Each part targets a specific skill:
- (a) Often asks for a description or identification (e.g., “Identify the type of selection illustrated”).
- (b) Requires calculation or interpretation (e.g., “Calculate the expected genotype frequencies using Hardy‑Weinberg”).
- (c) Demands explanation or prediction (e.g., “Explain how genetic drift could alter allele frequencies in a small isolated population”).
- (d) May involve drawing or labeling a diagram (e.g., “Add the missing branch to the cladogram”).
- (e) Sometimes asks for an evaluation of experimental design or a real‑world application.
- Answer Space – Each part includes lined space for a concise, bullet‑style response. Full sentences are not required, but clarity and completeness are essential.
Understanding this layout helps you allocate time effectively: spend roughly 2–3 minutes per part, leaving a few minutes at the end to review.
Sample FRQ Prompt and Model Answer
Below is a realistic example that mirrors the style of the Unit 7 Progress Check FRQ. Use it to practice identifying what each part is asking and how to structure a high‑scoring response.
Prompt
A population of Drosophila melanogaster has two alleles for wing shape: W (normal wings) and w (vestigial wings). Day to day, in a sample of 500 flies, the observed genotype counts are: WW = 245, Ww = 210, ww = 45. Because of that, persimilis* (vestigial wings). > (e) Sketch a simple phylogenetic tree showing the relationship among three Drosophila species: D. That's why melanogaster (normal wings), D. So compare these expected values to the observed counts and state whether the population appears to be evolving. > (d) If a new predator preferentially preys on flies with vestigial wings, describe how the allele frequencies would likely change over several generations.
simulans (normal wings), and *D. That's why > (c) Propose one evolutionary mechanism that could explain any deviation from Hardy‑Weinberg expectations observed in part (b). Now, >
(a) Calculate the allele frequencies of W and w in this population. > (b) Using the Hardy‑Weinberg equation, determine the expected genotype frequencies if the population is in equilibrium. Indicate which trait is likely ancestral.
Model Answer (concise, bullet‑style)
(a)
- Total alleles = 2 × 500 = 1000.
- Number of W alleles = (2 × 245) + 210 = 700.
- Number of w alleles = (2 × 45) + 210 = 300.
- p (frequency of W) = 700/1000 = 0.70.
- q (frequency of w) = 300/1000 = 0.30.
(b)
- Expected genotype frequencies:
- WW = p² = 0.70² = 0.49 → 0.49 × 500 = 245 flies.
- Ww = 2pq = 2 (0.70)(0.30) = 0.42 → 0.42 × 500 = 210 flies.
- ww = q² = 0.30² = 0.09 → 0.09 × 500 = 45 flies.
- Observed counts match expected exactly (245, 210, 45).
- Conclusion: The population is not deviating from Hardy‑Weinberg expectations; no evidence of evolution at this locus.
(c)
- If a deviation were observed (e.g., excess of heterozygotes), one plausible mechanism is heterozygote advantage (overdominance), where the Ww genotype confers higher fitness than either homozygote, maintaining both alleles in the population.
(d)
- Predation against vestigial wings reduces fitness of ww individuals.
- Selection pressure favors W allele → p will increase, q will decrease over generations.
- Eventually
(d) (continued)
- Eventually, the frequency of w would decline significantly, potentially approaching extinction if selection pressure remains strong. This demonstrates directional selection favoring the W allele, driving evolutionary change in the population.
(e)
- A simple phylogenetic tree would show a common ancestor branching into two lineages: one leading to D. persimilis (vestigial wings) and another splitting into D. melanogaster and D. simulans (both with normal wings).
- The ancestral trait is normal wings (W), as both D. melanogaster and D. simulans retain this trait, while D. persimilis exhibits the derived trait of vestigial wings. The tree reflects divergence due to evolutionary mechanisms such as mutation, selection, or genetic drift.
Taken together, these results illustrate how population genetics and phylogenetics operate at different scales but are governed by the same evolutionary principles. Whether examining short-term fluctuations within a single population or long-term divergence among species, the interplay of mutation, selection, drift, and inheritance shapes the genetic architecture of natural populations. The Drosophila population described in parts (a) through (c) is currently in Hardy–Weinberg equilibrium, indicating that allele frequencies are stable in the absence of evolutionary forces. Even so, part (d) shows that introducing a selective pressure—such as predation against vestigial wings—can quickly disrupt that equilibrium, driving directional selection and altering allele frequencies over generations. persimilis*. Which means part (e) places these microevolutionary changes in a broader historical context: the normal-wing condition appears ancestral in this clade, while vestigial wings represent a derived trait that arose in the lineage leading to *D. Understanding these mechanisms is essential for predicting how organisms respond to changing environments and for reconstructing the evolutionary history of life.
To detect the predicted shift in allele frequencies, researchers could employ a combination of phenotypic scoring and molecular genotyping. Even so, by marking individual flies with non‑lethal color tags and recapturing them across multiple generations, the proportion of heterozygotes (Ww) and homozygotes (WW, ww) can be quantified directly. Complementary allele‑specific PCR or sequencing assays would allow precise measurement of the W and w alleles in pooled DNA samples, enabling estimation of the selection coefficient (s) that quantifies the fitness advantage of the W allele under predation pressure. Experimental manipulation of predation risk — for example, raising cages with and without visual predators — demonstrates a measurable increase in W frequency within a few dozen generations, confirming the theoretical prediction of directional selection.
The genetic basis of the vestigial wing phenotype in D. persimilis offers a clear target for fine‑mapping studies. In practice, candidate genes such as vestigial (vg) and scalloped (sd) are known regulators of wing development in Drosophila. Because of that, a loss‑of‑function mutation in vg, for instance, could produce the reduced wing morphology observed in the field population. Still, sequencing the transcriptomes of individuals from both winged and vestigial lines would reveal differential expression patterns, while CRISPR‑mediated editing of the suspected locus in a laboratory strain would test causality. If the mutation is indeed a null allele, its spread in the wild would illustrate a classic case of phenotypic evolution driven by a single, easily observable trait.
Beyond the Drosophila system, the dynamics described illustrate broader principles applicable to many organisms. Day to day, in small, isolated populations, genetic drift can temporarily mask the effects of selection, allowing the w allele to persist at low frequencies despite its deleterious role in the presence of predators. In practice, conversely, high migration rates from neighboring populations with a higher W frequency could counteract local adaptation, maintaining polymorphism for longer periods. Modeling these interacting forces — selection, drift, mutation, and gene flow — provides a strong framework for predicting how traits respond to ecological changes such as the introduction of new predators, habitat alteration, or climate‑driven shifts in resource availability Not complicated — just consistent..
The official docs gloss over this. That's a mistake.
From a phylogenetic perspective, the placement of the vestigial wing trait on the Drosophila tree invites hypothesis testing about the timing of its origin. Molecular clock analyses, calibrated with fossil dates, suggest that the vg loss‑of‑function mutation arose approximately 2–3 million years ago, coincident with the divergence of the persimilis lineage. Comparative studies across the genus can reveal whether similar wing‑reduction events have occurred independently, supporting the notion of convergent evolution driven by comparable selective pressures That's the whole idea..
In a nutshell, the interplay of genetic equilibrium, selective pressures, and ancestral trait reconstruction demonstrates how microevolutionary processes manifest within a single population and how they are embedded within the larger tapestry of species history. By integrating empirical data with theoretical models, we gain a clearer picture of the mechanisms that shape biodiversity, informing both evolutionary theory and practical applications such as pest management and conservation genetics Not complicated — just consistent. No workaround needed..
