Biology • Year 12 • Module 6 • Lesson 7
Gene Pools — Mutation, Gene Flow and Genetic Drift
Lock in the population-level vocabulary and the three distinct processes that change a gene pool: mutation (adds new alleles), gene flow (transfers existing alleles), genetic drift (random change in small populations).
1. Term–definition match
The ten definitions below are shuffled. In the right-hand column write the matching term from this list: gene pool, allele frequency, mutation, gene flow, genetic drift, founder effect, bottleneck effect, population, allele, clone (of an allele copy). 10 marks
| # | Definition (shuffled) | Matching term |
|---|---|---|
| 1.1 | The total collection of alleles present across all individuals in a population. | |
| 1.2 | How common one allele is relative to other alleles of the same gene, usually expressed as a proportion or percentage of all copies in the population. | |
| 1.3 | A heritable change to DNA sequence; the only process that introduces a genuinely new allele into a gene pool. | |
| 1.4 | The transfer of alleles between populations through the migration of individuals and their subsequent reproduction. | |
| 1.5 | Random change in allele frequency from one generation to the next caused by chance sampling of which individuals reproduce. | |
| 1.6 | A form of genetic drift in which a small starting group establishes a new population whose allele frequencies differ by chance from the original source. | |
| 1.7 | A form of genetic drift in which a sharp reduction in population size (e.g. by disaster) randomly removes alleles and shifts the surviving frequencies. | |
| 1.8 | A group of interbreeding individuals of the same species occupying the same area at the same time; the unit at which a gene pool is defined. | |
| 1.9 | An alternative version of a gene; gene pools track how many copies of each of these exist in a population. | |
| 1.10 | An identical sequence copy of one allele produced by DNA replication, counted alongside all other copies when computing allele frequency. |
2. Cloze — the three processes
Fill each blank with the correct term from the word bank. Each term is used once. 10 marks
Word bank: new alleles • allele frequencies • populations • migration • chance • small • adaptive • founder effect • bottleneck • mutation
A gene pool is the total set of alleles in a population. Three processes change it. First, (2.1) _____________ creates (2.2) _____________; without it no genuinely new variation enters the gene pool. Second, gene flow moves alleles between (2.3) _____________ through (2.4) _____________ and subsequent breeding — it does not create alleles, only transfers existing ones. Third, genetic drift shifts (2.5) _____________ randomly because of (2.6) _____________ sampling of which individuals reproduce. Drift is strongest in (2.7) _____________ populations and is not (2.8) _____________ — its outcomes do not match what the environment "needs". Two named examples of strong drift are the (2.9) _____________, where a few individuals start a new population, and the (2.10) _____________, where a sharp reduction in population size removes alleles by chance.
3. True or false — with correction
For each statement, circle T or F. If the statement is false, write the corrected version. 8 marks (1 for T/F, 1 for the correction where needed)
3.1 Gene flow creates entirely new alleles by changing the DNA sequence of migrants. T / F
3.2 Genetic drift has a stronger proportional effect in small populations than in large ones. T / F
3.3 Genetic drift is adaptive — alleles become common because they are advantageous for the environment. T / F
3.4 Mutation is essential in the long term because it is the only source of genuinely new alleles in a gene pool. T / F
4. Function recall
Answer each in 1–2 sentences using precise terms from the lesson. 10 marks (2 each)
4.1 What is the role of mutation in changing a gene pool?
4.2 What is the role of gene flow between two neighbouring populations?
4.3 What is the role of genetic drift in a small isolated population?
4.4 Why does population size matter when chance events affect allele frequencies?
4.5 Why is it incorrect to say that gene flow and mutation are "the same kind of process because both add alleles to a population"?
5. Sort each scenario into one of three buckets
Below are six short scenarios. For each, write the dominant process responsible for the allele-frequency change: Mutation, Gene flow or Genetic drift (specify founder effect or bottleneck if it applies). 6 marks
| # | Scenario | Dominant process |
|---|---|---|
| 5.1 | A new DNA sequence variant appears in one cell of a parent's gonad and is inherited by some of that parent's offspring. | |
| 5.2 | A herd of deer moves from one valley to another and breeds with the resident deer, raising the frequency of one coat-colour allele in the resident gene pool. | |
| 5.3 | A volcanic eruption wipes out 95% of a beetle population. The survivors happen to carry a rare wing-pattern allele at unusually high frequency. | |
| 5.4 | Twelve birds blown off course colonise an empty island. By chance, three of them carry a rare blood-group allele that becomes common in the new island population. | |
| 5.5 | Honeybees regularly carry pollen between two patches of wildflowers, and a flower-colour allele rises in frequency in the second patch. | |
| 5.6 | In a population of 30 lizards, by chance only the four individuals carrying a particular tail-length allele happen to reproduce one season. |
6. Build a concept map
Draw labelled arrows between the six terms below to show how they connect. Each arrow must carry a linking phrase (e.g. "adds new", "transfers", "randomises", "is strongest in"). Aim for at least 6 labelled arrows. 6 marks
Supplied terms: gene pool · allele frequency · mutation · gene flow · genetic drift · small population.
Q1 — Term–definition matches
1.1 gene pool • 1.2 allele frequency • 1.3 mutation • 1.4 gene flow • 1.5 genetic drift • 1.6 founder effect • 1.7 bottleneck effect • 1.8 population • 1.9 allele • 1.10 clone (of an allele copy).
Q2 — Cloze answers (10 marks)
2.1 mutation • 2.2 new alleles • 2.3 populations • 2.4 migration • 2.5 allele frequencies • 2.6 chance • 2.7 small • 2.8 adaptive • 2.9 founder effect • 2.10 bottleneck.
Q3 — True / false with correction
3.1 False. Correction: gene flow moves existing alleles between populations via migration and reproduction; it does not create new alleles. Only mutation creates new alleles.
3.2 True.
3.3 False. Correction: genetic drift is random, not adaptive. An allele can become common by drift without conferring any environmental advantage.
3.4 True.
Q4.1 — Role of mutation
Mutation is the source of new alleles in the gene pool. It produces genuinely novel variation that gene flow and drift cannot create from nothing.
Q4.2 — Role of gene flow
Gene flow transfers existing alleles between populations through migration and subsequent reproduction. It can raise or lower an allele's frequency in the receiving population and tends to reduce genetic differences between exchanging populations.
Q4.3 — Role of genetic drift
Genetic drift changes allele frequencies by chance — i.e. by which individuals happen to reproduce. In a small isolated population it can shift frequencies sharply between generations, and over time it tends to reduce genetic diversity.
Q4.4 — Why population size matters for chance effects
In a small population, each individual contributes a large proportion of the next generation's alleles, so chance variations in who reproduces have a large proportional effect on allele frequency. In large populations, chance effects on different individuals tend to cancel out and the proportional change is small.
Q4.5 — Why mutation ≠ gene flow even though both can raise allele frequency
Mutation introduces a genuinely new sequence by changing DNA; gene flow only transfers existing alleles from another population. They differ in mechanism (DNA sequence change vs migration + reproduction) and in what they contribute (novel variation vs redistribution of existing variation), so they are not the same process.
Q5 — Scenario sort
5.1 Mutation (new DNA-sequence variant in a gonadal cell — passed to offspring).
5.2 Gene flow (migration + interbreeding between two populations).
5.3 Genetic drift — bottleneck (sharp population reduction, surviving allele frequencies are a chance sample of the original pool).
5.4 Genetic drift — founder effect (small group establishes a new population; chance over-representation of an allele).
5.5 Gene flow (pollen transfer between patches is movement of alleles between populations).
5.6 Genetic drift (chance in a small population — no migration, no new sequence). Accept also: "drift in a small population" without naming a sub-type.
Q6 — Sample concept map
A correct map should include arrows such as:
- mutation — adds new alleles to → gene pool
- gene flow — transfers alleles into → gene pool
- gene flow — changes → allele frequency
- genetic drift — randomises → allele frequency
- genetic drift — is strongest in → small population
- gene pool — is described by → allele frequency
Any biologically valid linking phrases are accepted. Award full marks for at least 6 correctly labelled arrows that respect causal direction.