AP Biology: Reproductive Isolation Practice Questions
Practice reproductive isolation with original AP Biology multiple-choice questions. Each item connects mechanisms of isolation, gene flow, selection, and speciation with a clear explanation.
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1. Two frog populations live in the same pond, but one group mates in early spring and the other mates in late summer. Which reproductive barrier is most directly described?
Explanation. Temporal isolation is a prezygotic barrier in which populations reproduce at different times, reducing opportunities for mating and gene flow.
2. Which example best represents behavioral isolation?
Explanation. Behavioral isolation occurs when differences in courtship signals or mating behaviors prevent individuals from recognizing each other as suitable mates.
3. A mule is usually sterile even though it develops from a horse and donkey mating. Which type of barrier does this illustrate?
Explanation. Reduced hybrid fertility is a postzygotic barrier. Fertilization occurs and the hybrid can survive, but the hybrid has greatly reduced ability to produce fertile offspring.
4. Two closely related snail species have shells that coil in opposite directions, making successful mating physically unlikely. Which barrier is this?
Explanation. Mechanical isolation is a prezygotic barrier caused by incompatible reproductive structures or physical fit, which prevents successful mating or gamete transfer.
5. Why do prezygotic barriers reduce gene flow more directly than postzygotic barriers?
Explanation. Prezygotic barriers act before a zygote forms, so they can prevent alleles from moving between populations through fertilization in the first place.
6. In a plant study, pollen from Species A lands on the stigma of Species B, but fertilization does not occur because the pollen tube fails to develop. Which barrier is most likely?
Explanation. Gametic isolation occurs when gametes or reproductive cells from different species are incompatible, preventing fertilization even if mating or pollen transfer occurs.
7. Two fish populations occupy the same lake. One breeds in shallow gravel beds, while the other breeds in dense aquatic plants. Which barrier best fits this pattern?
Explanation. Habitat isolation can occur when populations use different microhabitats for reproduction, so they are less likely to encounter each other as mates.
8. A hybrid plant generation is fertile, but its offspring have very low survival and fertility. Which postzygotic barrier is described?
Explanation. Hybrid breakdown occurs when first-generation hybrids are viable or fertile, but later-generation offspring show reduced viability or fertility.
9. Which evidence would best support the claim that two populations are becoming reproductively isolated?
Explanation. Reduced successful reproduction between populations is direct evidence of reproductive isolation and reduced gene flow.
10. How can geographic isolation contribute to reproductive isolation over time?
Explanation. When gene flow is reduced by a physical barrier, populations can diverge genetically. Over time, differences may produce prezygotic or postzygotic barriers.
11. A researcher compares mating calls in two insect populations and finds that females respond only to calls from their own population. What is the dependent variable in this experiment?
Explanation. The dependent variable is the measured response. In this experiment, the researcher manipulates the call type and measures whether females respond.
12. Which statement avoids a common misconception about speciation?
Explanation. Speciation is usually a population-level process involving reduced gene flow and accumulated differences. Barriers may be geographic, behavioral, temporal, mechanical, gametic, or postzygotic.
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FAQ
What is reproductive isolation in AP Biology?
Reproductive isolation is any barrier that reduces successful gene flow between populations by preventing mating, fertilization, or the production of viable and fertile offspring.
What is the difference between prezygotic and postzygotic barriers?
Prezygotic barriers act before a zygote forms, such as temporal, behavioral, habitat, mechanical, or gametic isolation. Postzygotic barriers act after fertilization, such as reduced hybrid viability, reduced hybrid fertility, or hybrid breakdown.
How does reproductive isolation connect to speciation?
When reproductive isolation reduces gene flow, populations can diverge through mutation, genetic drift, and natural selection. Over time, that divergence can lead to speciation.