20th Century Quiz
Questions: 16 · 10 minutes
1. Two partially diverged populations begin exchanging many migrants each generation. What is the most likely immediate effect of this renewed gene flow?
Their mutation rates become identical
Postzygotic barriers automatically become stronger
Their allele frequencies tend to become more similar
Each population immediately becomes a separate species
2. Which pairing best captures the central achievement of the 20th-century modern evolutionary synthesis?
Combining ecology with the inheritance of traits acquired during life
Combining Mendelian inheritance with Lamarckian use and disuse
Combining chromosome theory with the claim that evolution occurs only through mutation
Combining Darwinian natural selection with Mendelian genetics
3. Females of two closely related insect species respond to different courtship signals and therefore do not mate with males of the other species. Which barrier is this?
Behavioral isolation
Gametic isolation
Hybrid breakdown
Geographic isolation
4. In which population would genetic drift generally have the strongest effect?
A large mainland population receiving many migrants
A small population isolated on an island
A large population with frequent interbreeding across regions
A population whose size remains very large despite environmental change
5. In evolutionary biology, what does genetic isolation most directly mean?
The mutation rate of a population has permanently decreased
Two populations have reached identical allele frequencies
Gene flow between populations has become limited or absent
Natural selection has stopped acting on a population
6. How did Theodosius Dobzhansky contribute to the 20th-century modern evolutionary synthesis?
He revived inheritance through use and disuse as the main evolutionary mechanism
He connected genetic variation in natural populations with evolutionary change and speciation
He discovered the molecular double-helix structure of DNA
He argued that natural selection could not change allele frequencies
7. Fertilization occurs between two populations, but most hybrid embryos fail to develop fully. How should this barrier be classified?
A prezygotic barrier based on mating time
A prezygotic barrier based on courtship
A postzygotic barrier involving reduced hybrid viability
A geographic barrier preventing contact
8. Two marine species release eggs and sperm into the same water, but proteins on their gametes prevent fertilization between species. Which barrier is responsible?
Gametic isolation
Mechanical isolation
Temporal isolation
Reduced hybrid viability
9. Two frog populations live near the same pond, but one breeds in early spring and the other in midsummer. What barrier is operating?
Mechanical isolation
Temporal isolation
Habitat isolation
Reduced hybrid fertility
10. A few birds colonize a distant island. By chance, their allele frequencies differ markedly from those of the original mainland population. What best explains this pattern?
The founder effect
Hybrid breakdown
Assortative mating
Disruptive selection
11. Under the biological species concept associated with Ernst Mayr, species are primarily defined as which of the following?
Organisms that share nearly identical external features
Populations descending from any common ancestor, regardless of reproduction
Organisms occupying the same habitat and eating the same food
Populations that actually or potentially interbreed and are reproductively isolated from others
12. A plant undergoes chromosome doubling. It can reproduce with similarly doubled plants but cannot produce fertile offspring with the original population. What has most directly occurred?
Gene flow has eliminated differences between the populations
A behavioral barrier has developed through courtship preferences
Convergent evolution has made the populations genetically identical
Polyploidy has created reproductive isolation
13. A new canyon divides a beetle population. After many generations without interbreeding, the two populations develop reproductive barriers. Which process does this illustrate?
Allopatric speciation following geographic separation
Artificial selection directed by humans
Sympatric speciation caused by competition in one location
Convergent evolution between unrelated species
14. After gene flow stops, which process can make isolated populations diverge through random changes in allele frequencies?
Recombination within a single individual
Nonrandom mating
Stabilizing selection
Genetic drift
15. Two species can mate and produce healthy adult offspring, but those offspring cannot produce young of their own. Which reproductive barrier is demonstrated?
Habitat isolation
Reduced hybrid fertility
Behavioral isolation
Gametic isolation
16. Two bird populations have different plumage, but when they meet, they mate freely and produce fertile offspring. What conclusion is best supported?
They are definitely separate species under the biological species concept
Their offspring demonstrate reduced hybrid fertility
Plumage differences alone do not establish reproductive isolation
Their plumage difference proves that gene flow has stopped