AP Biology Unit 7 focuses on evolution, including concepts such as natural selection, speciation, genetic drift, and Hardy-Weinberg equilibrium. To help you prepare for the AP Biology exam, we have compiled a set of classified questions with detailed answers and explanations.
Key Topics in AP Biology Unit 7:
- Natural Selection and Adaptation
- Genetic Drift and Gene Flow
- Hardy-Weinberg Equilibrium
- Speciation and Evolutionary Patterns
- Phylogenetics and Cladograms
- Evidence for Evolution
Classified Questions with Answers and Explanations
Question 1: Natural Selection
Q: A population of beetles initially consists of green and brown individuals. Over time, the frequency of brown beetles increases due to predation on green beetles. Which mechanism best explains this change?
A: Natural Selection
Explanation: Predators prefer green beetles, leading to differential survival and reproduction. Brown beetles pass their traits to the next generation, increasing their frequency in the population.
Question 2: Hardy-Weinberg Equilibrium
Q: A certain population of frogs has 36% homozygous recessive individuals for a particular trait. Assuming Hardy-Weinberg equilibrium, what is the frequency of the dominant allele?
A: 0.4
Explanation: The recessive allele frequency (q) is the square root of 0.36, which is 0.6. Using p + q = 1, we find p = 1 – 0.6 = 0.4.
Question 3: Genetic Drift
Q: A small population of rabbits is isolated after a flood. Over time, the allele frequencies in this population change significantly. What process is responsible?
A: Genetic Drift
Explanation: Genetic drift occurs due to random changes in allele frequencies, especially in small populations. This can lead to loss of genetic variation and even fixation of alleles.
Question 4: Speciation
Q: Two populations of birds live on separate islands. Over thousands of years, they develop distinct mating calls and cannot interbreed. What type of speciation has occurred?
A: Allopatric Speciation
Explanation: Physical separation prevents gene flow, leading to the evolution of reproductive isolation and the formation of two distinct species.
More Questions
Question 1: Hardy-Weinberg Equilibrium
A population of beetles has two alleles for coloration: B (brown) and b (green). The frequency of the recessive allele (b) is 0.4. If the population is in Hardy-Weinberg equilibrium, what percentage of the population is heterozygous for this trait?
Answer:
The percentage of heterozygous individuals is 48% .
Explanation:
To solve this, we use the Hardy-Weinberg equation:p2+2pq+q2=1
where:
- p is the frequency of the dominant allele (B),
- q is the frequency of the recessive allele (b).
Given that q=0.4, we can calculate p:p+q=1⟹p=1−q=1−0.4=0.6
The frequency of heterozygotes (2pq) is:2pq=2(0.6)(0.4)=0.48
Thus, 48% of the population is heterozygous.
Question 2: Genetic Drift
A small island population of 50 lizards experiences a sudden volcanic eruption that kills 30 individuals. After the disaster, the allele frequencies in the population shift significantly. What evolutionary mechanism is primarily responsible for this change?
Answer:
The primary mechanism is genetic drift .
Explanation:
Genetic drift refers to random changes in allele frequencies that occur in small populations due to chance events. In this case, the volcanic eruption caused a bottleneck effect , where a significant portion of the population was eliminated randomly, leaving only a small subset of survivors. This random sampling leads to a shift in allele frequencies, which is characteristic of genetic drift.
Question 3: Directional Selection
In a population of rabbits, fur length varies from short to long. Over several generations, the average fur length increases because longer fur provides better insulation in a cold environment. Which type of selection is occurring here?
Answer:
This is an example of directional selection .
Explanation:
Directional selection occurs when individuals at one extreme of a phenotypic range have higher fitness than those at the other extreme. In this case, rabbits with longer fur are better adapted to the cold environment, leading to an increase in the average fur length over time as shorter-furred rabbits are selected against.
Question 4: Speciation
Two populations of birds live on opposite sides of a mountain range. Over time, they evolve into distinct species that cannot interbreed. What type of speciation is this?
Answer:
This is an example of allopatric speciation .
Explanation:
Allopatric speciation occurs when populations of the same species are geographically separated, preventing gene flow between them. Over time, genetic differences accumulate due to mutations, natural selection, and genetic drift, eventually leading to reproductive isolation. In this case, the mountain range acts as a geographic barrier, leading to the formation of two distinct species.
Question 5: Evidence for Evolution
Which of the following is NOT considered evidence for evolution? a) Homologous structures
b) Vestigial structures
c) Acquired characteristics
d) Fossil record
Answer:
c) Acquired characteristics
Explanation:
Acquired characteristics refer to traits that an organism develops during its lifetime due to environmental influences or use/disuse (e.g., muscles growing larger through exercise). These traits are not heritable and therefore do not contribute to evolution. In contrast:
- Homologous structures (e.g., the forelimbs of humans, bats, and whales) show shared ancestry.
- Vestigial structures (e.g., pelvic bones in whales) are remnants of features that were functional in ancestors.
- The fossil record provides direct evidence of changes in species over time.
Question 6: Sexual Selection
Male peacocks have elaborate tail feathers that make them more visible to predators but also attract mates. What type of sexual selection is this an example of?
Answer:
This is an example of intersexual selection .
Explanation:
Intersexual selection occurs when members of one sex (usually females) choose mates based on specific traits. In this case, female peacocks prefer males with elaborate tail feathers, even though these feathers may increase predation risk. This preference drives the evolution of exaggerated traits in males.
Question 7: Coevolution
Flowering plants and their pollinators (e.g., bees) often exhibit adaptations that benefit both species. For example, flowers may evolve specific shapes or colors to attract certain pollinators, while pollinators evolve specialized mouthparts to access nectar. What is this process called?
Answer:
This process is called coevolution .
Explanation:
Coevolution occurs when two or more species reciprocally affect each other’s evolution. In this case, the flowering plant and its pollinator exert selective pressures on each other, leading to the development of mutually beneficial adaptations.
Question 8: Founder Effect
A group of 10 birds migrates to a remote island and establishes a new population. Over time, the allele frequencies in this population differ significantly from those in the original mainland population. What evolutionary mechanism explains this difference?
Answer:
This is an example of the founder effect .
Explanation:
The founder effect occurs when a small group of individuals becomes isolated from a larger population, leading to reduced genetic diversity and altered allele frequencies. The new population reflects only the genetic variation present in the founding individuals, which may not represent the genetic diversity of the original population.
Final Thoughts
Practicing classified questions with explanations is one of the best ways to prepare for the AP Biology exam. Understanding the mechanisms of evolution, genetic variation, and speciation will help you answer both multiple-choice and free-response questions with confidence.
For more AP Biology practice questions and study resources, bookmark our site and stay tuned for the next unit breakdown
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