Speciation & Mechanisms of Evolution — Drills · Grade 10 Science

Chapter: Evolution, Ancestry & Biodiversity

What these drills covers

By the end of Speciation & Mechanisms of Evolution you should be able to:

6 questions, multiple choice, numeric and written answer, each with a worked explanation.

Vocabulary used: gene pool, allele frequency, mutation, gene flow, genetic drift, reproductive isolation, speciation.

Problem 1

Two populations are considered separate species when they
  1. look different
  2. live in different places
  3. no longer interbreed to produce fertile offspring under natural conditions
  4. have any genetic differences
Answer and explanation

no longer interbreed to produce fertile offspring under natural conditions

The biological species concept turns on reproductive isolation, not on appearance, location, or the mere existence of genetic differences.

Problem 2

Geographic isolation contributes to speciation by
  1. causing mutations to occur
  2. preventing gene flow so the populations can diverge
  3. making populations identical
  4. increasing population size
Answer and explanation

preventing gene flow so the populations can diverge

Separation stops the exchange of alleles, so mutation, drift, and different selective pressures can accumulate differences independently in each population.

Problem 3

An allele is at 50 percent in a large population. Twelve individuals found a new island population and 9 carry the allele. What is its frequency among the founders, as a percentage?
Answer and explanation

75 %

9 / 12 × 100 = 75 percent, well above the source population's 50 percent — a founder effect produced by chance in a small sample.

Problem 4

Genetic drift has its largest effects in
  1. very large populations
  2. small populations
  3. populations with high gene flow
  4. populations with no mutation
Answer and explanation

small populations

Chance variation in which individuals reproduce has proportionally larger effects when the population is small, so frequencies can shift substantially without selection.

Problem 5

Explain why gene flow between two populations slows their divergence.
Answer and explanation

Gene flow is the movement of alleles between populations through migration and interbreeding. It mixes the two gene pools, so differences that accumulate in one population are shared with the other instead of remaining local. Divergence requires differences to build up separately, so continuing gene flow works against it, which is why isolation is usually a precondition for speciation.

Response criteria

  • State a biologically accurate conclusion.
  • Show the data, mechanism, or calculation that supports it.
  • Include units, conditions, or limits where relevant.

Problem 6

Distinguish genetic drift from natural selection as causes of a change in allele frequency.
Answer and explanation

Natural selection changes frequencies because particular heritable variants raise their bearers' reproductive success, so the change is related to the alleles' effects. Genetic drift changes frequencies through chance in which individuals happen to reproduce, so the change is unrelated to the alleles' effects and can even reduce the frequency of a beneficial allele. Both alter populations, but only selection produces a consistent relationship between an allele's effect and its fate.

Response criteria

  • State a biologically accurate conclusion.
  • Show the data, mechanism, or calculation that supports it.
  • Include units, conditions, or limits where relevant.

Browse all courses