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Besides natural selection, what other forces change the genetic makeup of a population?

Discuss mechanisms of evolutionary change other than natural selection, including genetic drift, gene flow, non-random mating, and mutation (NGSSS SC.912.L.15.14; Reporting Category 2, Classification, Heredity, and Evolution).

A benchmark-level answer on the other mechanisms of evolution for the Florida Biology 1 EOC: genetic drift (including the bottleneck and founder effects), gene flow, non-random mating, and mutation, and how each changes a population's gene pool.

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  1. What this topic is asking
  2. Evolution and the gene pool
  3. Genetic drift
  4. Gene flow
  5. Non-random mating and mutation
  6. How they compare with natural selection
  7. Try this

What this topic is asking

The NGSSS benchmark SC.912.L.15.14 asks you to discuss mechanisms of evolutionary change other than natural selection: genetic drift, gene flow, non-random mating, and mutation. For the Florida Biology 1 EOC you need to recognize each mechanism from a scenario and explain how it changes a population's gene pool (its collection of alleles). The most-tested distinction is genetic drift (random change, especially in small populations) versus gene flow (movement of alleles between populations).

Evolution and the gene pool

Natural selection is the best-known mechanism (favorable traits become more common), but the benchmark focuses on four others.

Genetic drift

The key feature of drift is randomness: alleles change in frequency, or are even lost, by chance, not because they help the organism survive.

Gene flow

The clue for gene flow is movement between populations: individuals arriving from elsewhere and breeding, introducing their alleles.

Non-random mating and mutation

  • Non-random mating. When organisms choose mates based on traits (for example, females selecting males with a particular display), some alleles are passed on more than others, changing the gene pool. Mating is not random with respect to those traits.
  • Mutation. A mutation is a change in an organism's DNA. Mutations create new alleles, and so they are the ultimate source of all genetic variation. Without mutation, there would be no new variation for the other mechanisms (or natural selection) to act on. (Mutation is covered in detail in mutations and genetic variation.)

How they compare with natural selection

The big contrast: natural selection is not random, it favors traits that improve reproductive success. Genetic drift and mutation are random with respect to fitness; they change the gene pool by chance (drift) or by creating new variation (mutation), not because a trait is beneficial. Gene flow simply moves existing alleles around. All four can drive evolution alongside natural selection.

Try this

Q1. State the difference between genetic drift and gene flow. [2]

  • Cue. Genetic drift is a random change in allele frequencies within a population (strongest when small); gene flow is the movement of alleles between populations by migration and breeding.

Q2. Explain why mutation is described as the ultimate source of genetic variation. [2]

  • Cue. Mutation changes DNA and creates new alleles; without it, there would be no new variation for natural selection or the other mechanisms to act on.

Exam-style practice questions

Practice questions written in the style of FLDOE exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.

FL Biology 1 EOC (2023 released style)1 marksA volcanic eruption kills most of a beetle population at random, leaving a few survivors whose allele frequencies differ from the original population by chance. Which mechanism of evolution is this? (A) Natural selection. (B) Genetic drift (bottleneck effect). (C) Gene flow. (D) Adaptation.
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A 1-point multiple-choice item on genetic drift.

The correct answer is B. A random event (the eruption) drastically reduced the population, and the survivors' allele frequencies differ by chance, not because of any survival advantage. This is the bottleneck effect, a form of genetic drift. It is not natural selection (no advantage was involved), and gene flow involves movement between populations.

Random change in allele frequency, especially in a small population, equals genetic drift.

FL Biology 1 EOC (2024 released style)1 marksIndividuals from one population of flowers migrate to a nearby population and breed, introducing new alleles. Which mechanism of evolution does this describe? (A) Genetic drift. (B) Gene flow. (C) Mutation. (D) Non-random mating.
Show worked answer →

A 1-point item on gene flow.

The correct answer is B. Gene flow is the movement of alleles between populations, usually by migration and breeding. New individuals bring new alleles into the gene pool. Genetic drift is random change within a population, mutation creates new alleles, and non-random mating is choosing mates by trait, so A, C, and D are different mechanisms.

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