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Genetics and Evolution

Evolution and speciation Practice Questions

20 free Evolution and speciation practice questions for the USMLE Step 1. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.

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Question 1 of 20 Medium

Which of the following best defines biological evolution in a population genetics context?

  1. A Change in an individual’s DNA during its lifetime
  2. B Change in allele frequencies within a population over time
  3. C Change in protein structure caused by a mutation
  4. D Change in a species driven by individual migration events

Correct answer: Change in allele frequencies within a population over time

Evolution in population genetics refers to changes in allele frequencies across generations within a population, not changes within an individual’s lifetime.

Question 2 of 20 Medium

Which of the following is NOT considered a primary mechanism driving evolution?

  1. A Natural selection
  2. B Genetic drift
  3. C Gene flow (migration)
  4. D Somatic cell mutation

Correct answer: Somatic cell mutation

Somatic cell mutations affect only the individual and are not heritable in a population; evolution requires heritable changes in allele frequencies — mechanisms are mutation (in gametes), natural selection, genetic drift, and gene flow.

Question 3 of 20 Medium

What effect does genetic drift most strongly have on a population?

  1. A Consistently favoring beneficial alleles over deleterious ones
  2. B Randomly altering allele frequencies, mainly in small populations
  3. C Increasing gene flow and mixing between separate populations
  4. D Generating entirely new mutations in the gene pool

Correct answer: Randomly altering allele frequencies, mainly in small populations

Genetic drift causes random fluctuations in allele frequencies, and its impact is greatest in small populations where sampling effects are more pronounced.

Question 4 of 20 Medium

What is the consequence of gene flow between two previously isolated populations?

  1. A Increased genetic differentiation
  2. B Decreased genetic variation within each population
  3. C Increased homogenization of allele frequencies
  4. D Formation of a new species immediately

Correct answer: Increased homogenization of allele frequencies

Gene flow (migration) introduces new alleles into a population or mixes gene pools between populations, which tends to homogenize allele frequencies and reduce divergence.

Question 5 of 20 Medium

Which condition must be met for populations to undergo speciation?

  1. A Continuous gene flow between the two populations
  2. B Reproductive isolation that prevents interbreeding
  3. C Identical environmental pressures acting on both groups
  4. D Large population size that minimizes any genetic drift

Correct answer: Reproductive isolation that prevents interbreeding

Speciation requires reproductive isolation, so that gene flow is limited or absent — allowing genetic divergence and formation of distinct species.

Question 6 of 20 Medium

What is the most common mode of speciation observed in nature, especially when populations are geographically separated?

  1. A Sympatric speciation
  2. B Allopatric speciation
  3. C Parapatric speciation
  4. D Hybrid speciation

Correct answer: Allopatric speciation

Allopatric speciation — speciation through geographic isolation — is widely regarded as the most common mode, because physical barriers prevent gene flow and allow divergent evolution.

Question 7 of 20 Medium

In allopatric speciation, which force tends to contribute most to genetic divergence between the geographically separated populations?

  1. A Ongoing gene flow between the populations
  2. B Genetic drift together with natural selection
  3. C Somatic mutation in non-reproductive cells
  4. D Horizontal gene transfer between individuals

Correct answer: Genetic drift together with natural selection

Once gene flow is blocked by geographic separation, genetic drift and natural selection act independently in each isolated population, promoting divergence in allele frequencies and phenotypes over time.

Question 8 of 20 Medium

Which scenario best illustrates peripatric speciation?

  1. A A large population divided by a rising mountain range
  2. B A small group colonizing a remote island and diverging from the mainland
  3. C Continuous populations diverging gradually across an environmental gradient
  4. D Two populations in the same area evolving separately without interbreeding

Correct answer: A small group colonizing a remote island and diverging from the mainland

Peripatric speciation involves a small, peripheral population becoming isolated (such as on an island), leading to rapid genetic divergence from the mainland population — a special case of allopatric speciation.

Question 9 of 20 Medium

Which type of speciation can occur even when populations inhabit the same geographic area (i.e., without physical separation)?

  1. A Allopatric speciation
  2. B Peripatric speciation
  3. C Sympatric speciation
  4. D Vicariant speciation

Correct answer: Sympatric speciation

Sympatric speciation occurs without geographic isolation — new species arise within the same area, often through ecological, behavioral, or genetic (e.g., polyploidy) divergence that reduces gene flow.

Question 10 of 20 Medium

Which factor can facilitate sympatric speciation in plants more readily than in animals?

  1. A Behavioral isolation
  2. B Polyploidy (genome duplication)
  3. C Geographic separation
  4. D Large body size

Correct answer: Polyploidy (genome duplication)

Polyploidy — duplication of the entire chromosome set — can instantly create reproductive isolation within a population, a mechanism particularly common in plants and conducive to sympatric speciation.

Question 11 of 20 Medium

What is adaptive radiation?

  1. A Evolution of similar traits in unrelated species over time
  2. B Rapid diversification of a lineage into species suited to different niches
  3. C Gradual change accumulating within a single species over time
  4. D Extinction of one species followed by the evolution of another

Correct answer: Rapid diversification of a lineage into species suited to different niches

Adaptive radiation refers to rapid speciation from a common ancestor into many species, each adapted to exploit distinct ecological niches — explaining much of biodiversity.

Question 12 of 20 Medium

Which phenomenon can lead to loss of genetic variation and increase the probability of fixation of deleterious alleles in small populations?

  1. A Gene flow
  2. B Natural selection favoring heterozygotes
  3. C Genetic drift (bottleneck effect)
  4. D Adaptive radiation

Correct answer: Genetic drift (bottleneck effect)

A population bottleneck — a sharp reduction in population size — increases the impact of genetic drift, which can randomly fix alleles (even deleterious ones) and reduce genetic variation.

Question 13 of 20 Medium

Which outcome is LEAST likely if two populations remain in contact and continue exchanging migrants (gene flow)?

  1. A Reproductive isolation leading to speciation
  2. B Genetic homogenization across the populations
  3. C Decrease in genetic differentiation over time
  4. D Increasingly shared allele frequencies between them

Correct answer: Reproductive isolation leading to speciation

Ongoing gene flow homogenizes allele frequencies and reduces divergence, making speciation via reproductive isolation highly unlikely while migration continues.

Question 14 of 20 Medium

Which process introduces new heritable variation into a population that can be acted upon by evolutionary forces?

  1. A Genetic drift
  2. B Mutation
  3. C Gene flow
  4. D Adaptive radiation

Correct answer: Mutation

Mutation produces novel alleles in gametes, providing the raw genetic variation necessary for evolution; without mutation, other mechanisms have no new variants to act upon.

Question 15 of 20 Medium

How can sexual selection contribute to speciation within a population?

  1. A By steadily increasing overall population size
  2. B By shaping mate choice, driving reproductive isolation without geographic barriers
  3. C By preventing any genetic divergence among individuals
  4. D By promoting continuous gene flow across the population

Correct answer: By shaping mate choice, driving reproductive isolation without geographic barriers

Sexual selection can lead to preferential mating within subgroups (e.g., based on traits), reducing gene flow across subgroups and facilitating reproductive isolation — an important driver of sympatric speciation.

Question 16 of 20 Medium

Which pattern of evolution describes the evolution of similar traits independently in unrelated lineages due to similar selective pressures?

  1. A Adaptive radiation
  2. B Divergent evolution
  3. C Convergent evolution
  4. D Peripatric speciation

Correct answer: Convergent evolution

Convergent evolution occurs when unrelated species evolve similar adaptations independently because they face similar environmental pressures, even though they do not share a recent common ancestor.

Question 17 of 20 Medium

What does the term “reproductive isolation” refer to in the context of speciation?

  1. A A permanent change in the chromosome number of a population
  2. B Any barrier that prevents gene flow between populations
  3. C The gradual extinction of an isolated population
  4. D The rapid diversification seen in adaptive radiation

Correct answer: Any barrier that prevents gene flow between populations

Reproductive isolation includes all pre-zygotic and post-zygotic mechanisms that prevent interbreeding or viable offspring between populations — a key requirement for speciation.

Question 18 of 20 Medium

Which of the following best describes parapatric speciation?

  1. A Speciation driven by complete geographic separation of populations
  2. B Speciation across an environmental gradient in adjacent populations
  3. C Speciation within a uniform environment lacking any physical barriers
  4. D Speciation that occurs exclusively in flowering plant lineages

Correct answer: Speciation across an environmental gradient in adjacent populations

Parapatric speciation occurs when populations are contiguous but inhabit different ecological niches or environmental gradients, leading to reduced gene flow and gradual divergence despite geographic proximity.

Question 19 of 20 Medium

Why is speciation considered a macroevolutionary process, distinct from microevolution?

  1. A Because it involves adaptive changes within a single generation
  2. B Because it involves allele-frequency changes within one population
  3. C Because it yields new species through reproductive isolation, not just allele shifts
  4. D Because it occurs only in plant lineages and never in animals

Correct answer: Because it yields new species through reproductive isolation, not just allele shifts

Speciation results in the emergence of reproductively isolated populations (new species), which is a macroevolutionary change — beyond microevolutionary allele-frequency shifts within a single species.

Question 20 of 20 Medium

Which evolutionary scenario is most conducive to rapid speciation — for example, adaptive radiation — when a colonizing species reaches an unoccupied habitat with many available ecological niches?

  1. A Large gene flow maintaining ties with the ancestral population
  2. B High genetic drift acting with no selection pressure at all
  3. C Strong ecological selection combined with ecological opportunity
  4. D Constant, unchanging environmental conditions and no new mutation

Correct answer: Strong ecological selection combined with ecological opportunity

When a species colonizes a new environment with many empty niches, strong ecological selection pressures coupled with ecological opportunity can drive rapid diversification and speciation (adaptive radiation).

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