Speciation & Mechanisms of Evolution — Practice · Grade 10 Science
Chapter: Evolution, Ancestry & BiodiversityWhat this practice covers
By the end of Speciation & Mechanisms of Evolution you should be able to:
- I can describe how mutation, gene flow, genetic drift, and natural selection change the allele frequencies of a population.
- I can explain how reproductive isolation causes one population to split into two separate species.
10 questions, multiple choice, written answer and numeric, each with a worked explanation.
Vocabulary used: gene pool, allele frequency, mutation, gene flow, genetic drift, reproductive isolation, speciation.
Problem 1
- Gene flow
- Genetic drift
- Natural selection
- Mutation
Answer and explanation
Mutation
Mutation is the only mechanism that creates entirely new alleles. Gene flow, drift, and selection can only shuffle, spread, or remove variation that mutation first produced.
Problem 2
- small populations
- very large populations
- populations with high gene flow
- populations under strong natural selection
Answer and explanation
small populations
Drift is random change in allele frequencies. In small populations, chance events (like which few individuals happen to reproduce) can swing allele frequencies dramatically; in large populations these chance effects average out.
Problem 3
Answer and explanation
Gene flow moves alleles between populations and keeps their gene pools mixed and similar, so they can't diverge into separate species. Reproductive isolation stops that exchange of genes, letting mutation, drift, and selection push each population's gene pool in its own direction until they become separate species.
Problem 4
- a prezygotic reproductive barrier
- the founder effect (a form of genetic drift)
- gene flow between the island and mainland
- natural selection favoring island traits
Answer and explanation
the founder effect (a form of genetic drift)
A small group founding a new population carries only a random sample of the original gene pool, so its allele frequencies differ by chance. This is the founder effect, a type of genetic drift.
Problem 5
Answer and explanation
48 copies
40 survivors x 2 copies each = 80 total gene copies. 0.60 x 80 = 48 copies of the A allele.
Problem 6
Answer and explanation
Genetic drift through a bottleneck is consistent with the scenario.
Survival in the prompt is unrelated to the allele's benefit.
A small survivor sample can differ by chance.
Response criteria
- Use the stated conditions.
- Show the evidence or calculation.
- Explain the conclusion and any stated limitation.
Problem 7
Hints
Random sampling differs from trait-dependent reproductive success.
Answer and explanation
Gene flow.
Problem 8
Hints
State what the supplied observations or conditions establish, and separate that from any assumption.
Answer and explanation
Reproductive isolation and divergence must be established; separation alone does not guarantee them.
Problem 9
Answer and explanation
No. The stated random sampling can change frequency without a fitness difference; mechanism evidence is needed.
Genetic drift is chance change in allele frequencies associated with finite reproductive sampling. A bottleneck sharply reduces population size; a founder effect concerns a small group establishing a new population. Random loss can alter representation and remove variants without proving a selective advantage. Drift can occur alongside selection and gene flow. The source gold fraction here is 6/24=1/4, while the selected survivor sample is 3/6=1/2. This example illustrates a possible outcome, not a required direction for all bottlenecks.
No. The stated random sampling can change frequency without a fitness difference; mechanism evidence is needed.
Response criteria
- Read the structures, axes, directions and units correctly.
- Connect the evidence with the biological mechanism.
- Respect stated model assumptions and distinguish an observation from a further inference.
Problem 10
Answer and explanation
The source fraction is 30%, the founder fraction 60%. A random sample can yield that change; it does not alone demonstrate gold advantage, new mutation or completed speciation.
The source fraction is 30%, the founder fraction 60%. A random sample can yield that change; it does not alone demonstrate gold advantage, new mutation or completed speciation.
Response criteria
- Use the stated measurements or conditions, with correct units.
- Connect the result to the biological mechanism or evidence relationship.
- Identify the assumption, model limit or further evidence requested.