Mutation, Alleles and Genetic Change
You'll be able to classify examples as new allele creation or allele reshuffling.
In 1945, Alexander Fleming warned that exposing microbes to insufficient penicillin could select resistant populations. Resistance does not appear because bacteria "decide" to adapt: random mutations arise first, then antibiotic exposure changes which alleles become common. Module 6 opens by separating new allele creation from allele reshuffling.
Connect mutation to selection
Make a prediction and identify the distinction this lesson will resolve.
Practise this lesson
Four printable worksheets that build from the foundations up to exam-style questions, start at whatever level suits you.
Mutation is the source of new alleles in a population.
A student says, "Bacteria exposed to antibiotics mutate so they can survive." That statement sounds plausible because resistant bacteria often become common after antibiotic treatment.
Write whether you agree or disagree. In your explanation, distinguish between a mutation appearing, an allele already existing, and selection increasing its frequency.
Build the mutation model
Define the key terms and classify how DNA changes create alleles.
Know
- Mutation creates new alleles.
- Meiosis and fertilisation usually reshuffle existing alleles.
- The gene pool is population-level, not individual-level.
Understand
- Random mutation and natural selection are separate steps.
- Not all genetic variation comes from the same process.
- Module 6 extends Module 5 rather than replacing it.
Apply
- Classify examples as new allele creation or allele reshuffling.
- Explain why mutation is population-relevant over time.
- Use accurate HSC language about genetic change.
Core Content
Foundation idea · the source of new alleles
Before penicillin was introduced in the 1940s, some bacterial cells already carried rare mutations that happened to reduce antibiotic sensitivity. Those cells reproduced; their descendants survived treatment; within years the resistant allele had spread through hospital populations, not because bacteria "decided" to change, but because a random DNA change that already existed became advantageous once the environment shifted.
A mutation is a change in DNA sequence. Because genes are DNA sequences, mutation can produce a new version of a gene, which is a new allele. This matters because Module 5 mostly dealt with inheritance of existing alleles. Module 6 asks where new alleles come from in the first place.
Mutation is random with respect to need. The environment does not instruct an organism to make the exact change it needs. Instead, a mutation happens first. If that mutation affects survival or reproduction, natural selection may later change how common that allele becomes in the population.
Mutation is a change in DNA sequence and the ultimate source of new heritable alleles, while meiosis and fertilisation reshuffle alleles that already exist.
Pause, copy the highlighted definition into your book before moving on.
Mutation is the ultimate source of new _____ in a population.
Represent genes, alleles and gene pools
Separate three levels of genetic language and compare sources of variation.
Language precision · three levels
We just saw that mutation is the source of new alleles. That raises a question: how exactly do gene, allele and gene pool relate to each other? This card answers it → three levels of genetic language.
A gene is a DNA sequence with a biological function, often coding for a protein or functional RNA. An allele is a variant of that gene. A gene pool is the total set of alleles present in a population. Exam answers often lose marks by mixing these levels.
Gene
- A named DNA region such as a pigment gene.
- Exists at a locus on a chromosome.
- Can have multiple allele forms.
Allele
- A specific version of the gene.
- Examples might differ by one or more DNA bases.
- New alleles appear by mutation.
Gene Pool
- Population-level collection of alleles.
- Changes over generations, not within one individual.
- Affected by mutation, gene flow and drift later in this module.
A gene is a functional DNA region at a locus; an allele is a specific variant of that gene; the gene pool is the total collection of alleles in a population, these three levels must not be confused in exam responses.
Add the highlighted point to your notes before the check below.
Which term means the total collection of alleles present in a population?
Build from Module 5 · recombining existing alleles
We just saw that gene, allele and gene pool are distinct concepts. That raises a question: if mutation makes new alleles, what role do meiosis and fertilisation actually play? This card answers it → reshuffling existing variation.
Module 5 showed that meiosis generates variation through independent assortment and crossing over, and fertilisation combines gametes randomly. Both processes matter greatly for variation, but they normally work by recombining alleles that already exist in the parental population.
| Process | Main effect | Creates a new allele? | Why it matters |
|---|---|---|---|
| Mutation | Changes DNA sequence | Yes | Introduces a genuinely new variant into the population |
| Meiosis | Reshuffles chromosomes and alleles | Not usually | Produces genetically different gametes from existing alleles |
| Fertilisation | Combines gametes randomly | No | Creates new allele combinations in offspring |
The distinction is central to the inquiry question. Mutation creates new alleles. Meiosis and fertilisation spread and recombine alleles already available.
Meiosis and fertilisation do not create new alleles, they reshuffle and recombine alleles that already exist; only mutation produces a genuinely new allele by changing the DNA sequence itself.
Pause, write the highlighted distinction into your book.
Meiosis and fertilisation normally create brand-new alleles that did not exist before.
A mutation is a permanent change in the DNA sequence that can create new alleles.
All mutations are harmful to the organism in which they occur.
Distinguish natural and induced change
Place mutation, population change and biotechnology on the Module 6 roadmap.
Module roadmap · mutation → gene pools → biotechnology
We just saw that meiosis and fertilisation reshuffle rather than create alleles. That raises a question: how does this distinction structure the rest of the module? This card answers it → the module roadmap.
This lesson opens the module by drawing a boundary line. The first half of Module 6 focuses on natural genetic change: mutation, variation, gene pools and population processes. The second half moves to biotechnology and deliberate human intervention.
1. DNA changes
A mutation changes a DNA sequence in one cell or lineage.
2. New allele exists
If the mutation occurs in a gene region, a new allele can be present.
3. Population consequences
The new allele may remain rare, disappear, or increase in the gene pool depending on later processes.
Natural processes
Selection, drift and gene flow affect allele frequency over generations.
Existing variation
Meiosis and fertilisation keep reshuffling allele combinations.
Human technologies
Later lessons examine cloning, recombinant DNA and other induced genetic change.
Mutation is the entry point for new alleles, but many later processes control their fate.
Module 6 has two halves: natural genetic change (mutation, variation, gene pools) and human-induced biotechnology, mutation supplies new alleles, while selection, drift and gene flow then decide their fate in a population's gene pool.
Pause, copy the highlighted principle into your notes before continuing.
A mutation is random with respect to need. What does natural selection do afterwards?
Apply the distinctions
Classify examples, repair population language and check misconceptions.
Activities
New Allele or Reshuffled Allele?
For each example, decide whether it best illustrates a new allele being created, existing alleles being reshuffled, or selection changing frequency.
- A single DNA base change produces a gene variant never seen before in the population.
- Two siblings inherit different combinations of their parents' alleles.
- After antibiotic treatment, resistant bacteria become much more common.
- A child inherits one allele from each parent for eye colour.
Population Language Repair
Rewrite each loose statement using precise Module 6 language.
- "Bacteria mutate because they need to survive antibiotics."
- "Fertilisation makes brand-new alleles."
- "A gene pool is all the genes in one organism."
Synthesise the lesson
Capture the biological claim, mechanism and exam-ready comparison.
Core biological claim
- Mutation is the source of new alleles in populations.
Mechanism or process
- A DNA sequence changes, producing a new gene variant that may later enter or spread through a gene pool.
Common exam error
- Saying meiosis or fertilisation creates all new alleles, or saying mutation happens because it is needed.
Evaluative sentence starter
- "Although meiosis and fertilisation increase variation, only mutation introduces genuinely new alleles into a population."
Explain how mutation introduces new alleles into a population.
This is the module's own inquiry question. Explain asks for the mechanism from a change in DNA to a change in the gene pool, so the answer has to travel that whole distance rather than stopping at the molecule.
Plan: name the principle, take each stage as a linked pair, then answer the question directly at population level.
An allele is one version of a gene, and a population's gene pool is the total collection of alleles its members carry. Mutation is a change in the base sequence of DNA, so it is the only process that can produce a version of a gene that did not previously exist anywhere in that pool.
A mutation occurs in a single cell of a single organism, through an error in DNA replication or through damage by a mutagen. At that moment the new allele exists in one copy, in one individual, which is why mutation on its own changes a gene pool only very slightly.
The mutation enters the gene pool only if it occurs in a germ-line cell, since only gametes pass DNA to the next generation. A mutation in a somatic cell may affect that individual, and may cause disease, but it is not transmitted and so leaves the population's alleles unchanged.
Once inherited, the new allele's frequency rises or falls through natural selection, genetic drift and gene flow rather than through further mutation. Mutation therefore supplies the raw material and the other processes determine what happens to it, which is why mutation is described as the ultimate but not the immediate source of genetic change.
An allele is one version of a gene and a population's gene pool is the total collection of alleles its members carry, so because mutation is a change in the base sequence of DNA it is the only process that can produce a version of a gene not previously present in that pool. A mutation arises in a single cell of a single organism, by replication error or by damage from a mutagen, so the new allele begins as one copy in one individual. It enters the gene pool only if it occurs in a germ-line cell, since only gametes transmit DNA to the next generation — a somatic mutation may harm that individual without altering the population's alleles at all. Once inherited, the allele's frequency then rises or falls through natural selection, genetic drift and gene flow rather than through further mutation. Mutation therefore introduces new alleles by altering germ-line DNA, supplying the variation that the other processes act upon, which is why it is the ultimate rather than the immediate source of genetic change in a population.
Distinguish between a new allele and a reshuffled combination of existing alleles, using an example of each.
Distinguish asks for the point of difference, stated so that either case can be identified from it. Two separate descriptions placed side by side is not a distinction.
Plan: state the criterion, apply it to each case with an example, then give the test that separates them.
The point of difference is whether the total set of alleles present in the population changes. A new allele adds a version of a gene that did not previously exist; a reshuffled combination rearranges versions that were already there.
Mutation produces a new allele. A substitution in the haemoglobin gene changed a single base and produced the HbS allele, a version of that gene that had not existed before, so the number of distinct alleles in the population increased by one.
Meiosis and fertilisation produce new combinations of existing alleles. Crossing over and independent assortment place alleles together in a gamete in arrangements not seen in the parent, and fertilisation pairs two such gametes, so an offspring may carry a combination unique in the population while every individual allele in it is old.
The two are separated by asking whether the DNA sequence itself is different from any sequence present before. If it is, the change is a mutation and a new allele; if the sequences are all pre-existing and only their pairing is novel, the change is reshuffling. This is why only mutation increases the total genetic diversity of a gene pool, while meiosis and fertilisation redistribute it.
The point of difference is whether the total set of alleles present in the population changes: a new allele adds a version of a gene that did not previously exist, while a reshuffled combination rearranges versions already present. Mutation produces the first — a substitution in the haemoglobin gene changed one base and produced the HbS allele, so the number of distinct alleles in the population increased. Meiosis and fertilisation produce the second, since crossing over and independent assortment place existing alleles into gametes in arrangements the parent did not carry and fertilisation pairs two such gametes, so an offspring may hold a combination unique in the population while every allele within it is old. The two are separated by asking whether the DNA sequence itself differs from any sequence present before: if it does the change is a mutation and a new allele, and if only the pairing is novel the change is reshuffling. That is why only mutation increases the total genetic diversity of a gene pool, while meiosis and fertilisation redistribute the diversity that is already there.
Practise the distinctions
Answer fresh questions, explain your reasoning and compare model responses.
A fresh set drawn from this lesson's question bank, feedback shown immediately. +5 XP per correct · +25 XP all correct
Pick your answer, then rate your confidence, that tells the system what to drill next.
UnderstandBand 3(3 marks) 1. Define mutation, allele and gene pool, then explain how they are linked.
AnalyseBand 4(4 marks) 2. Compare the roles of mutation, meiosis and fertilisation in producing genetic variation.
EvaluateBand 5–6(5 marks) 3. Evaluate the statement: "Antibiotics cause bacteria to mutate so they can survive." Use the antibiotic resistance anchor in your answer.
Show all answers
Multiple choice
MC answers and full explanations are shown inline as you complete each question. Use the retry button to attempt a fresh set from the lesson bank.
Activity 1, New allele or reshuffled allele?
1. Mutation. A changed base sequence can create a new allele.
2. Meiosis and fertilisation reshuffling existing alleles.
3. Selection changing frequency after the fact. Mutation may have produced resistance earlier, but antibiotics select for the resistant allele.
4. Fertilisation and inheritance of existing alleles, not creation of a new allele.
Activity 2, Population language repair
1. Mutations occur randomly with respect to need. If a mutation is advantageous, natural selection may increase its frequency.
2. Fertilisation creates new combinations of existing alleles, but mutation creates new alleles.
3. A gene pool is the total collection of alleles present in a population.
Short Answer Model Responses
Q1 (3 marks): A mutation is a change in DNA sequence [1]. An allele is a variant form of a gene [1]. A gene pool is the total collection of alleles in a population [1]. These are linked because mutation can create a new allele, which may then enter the population gene pool.
Q2 (4 marks): Mutation creates new alleles by changing DNA sequence [1]. Meiosis increases variation by reshuffling chromosomes and alleles through processes such as independent assortment and crossing over [1]. Fertilisation increases variation by combining gametes randomly [1]. Therefore mutation is the source of genuinely new alleles, while meiosis and fertilisation mostly create new combinations of existing alleles [1].
Q3 (5 marks): The statement is inaccurate because antibiotics do not cause bacteria to produce the exact mutation they need [1]. Mutation occurs randomly with respect to need [1]. A resistant allele may already exist or arise by chance in some bacteria [1]. When antibiotics are used, susceptible bacteria die while resistant bacteria survive and reproduce, so the resistant allele becomes more common [1]. Therefore antibiotic resistance is best explained as selection acting on random mutation, not purposeful mutation caused by the antibiotic [1].
Review and reflect
Retrieve the big ideas, test your fluency and revisit your opening claim.
New allele
Produced directly by mutation changing the DNA sequence.
Reshuffled variation
Produced by meiosis and fertilisation recombining alleles already present.
Population level
A gene pool is all alleles in a population, not one organism.
Most common trap
Saying mutation happens because the organism needs to adapt.
Rapid-fire questions on mutation, alleles, gene pools and natural vs induced genetic change. Beat the boss to bank a tier, gold (perfect + fast), silver (80%+), or bronze (cleared).
Return to Alexander Fleming's 1945 warning about underdosing penicillin. You should now be able to explain why resistant mutations arise randomly rather than in response to need, while antibiotic exposure provides selection pressure that can increase their frequency. Mutation created the allele; natural selection changed the gene pool.