Mutation, Alleles and Genetic Change
Bacteria do not mutate because they need antibiotic resistance. Random mutations occur first, and natural selection later increases the frequency of any allele that happens to help survival. Module 6 starts by separating new allele creation from the reshuffling of alleles that already exist.
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.
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
If a population already contains alleles A and a, meiosis and fertilisation can only rearrange those existing variants. They do not create a brand-new allele unless a mutation occurs.
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.
Overview of mutation as the ultimate source of genetic change.
What to write in your book
- Mutation = a change in DNA sequence → can produce a new allele.
- Module 5 = inheritance of existing alleles; Module 6 = where new alleles come from.
- Mutation is random with respect to need (not caused by need).
- Selection acts AFTER a mutation already exists.
Mutation is the ultimate source of new _____ in a population.
Language precision · three levels
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.
What to write in your book
- Gene = a functional DNA region at a locus.
- Allele = a specific variant of that gene (new ones arise by mutation).
- Gene pool = all alleles in a population (population-level).
- Don't mix the levels — a common mark-losing error.
Which term means the total collection of alleles present in a population?
Build from Module 5 · recombining existing alleles
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.
What to write in your book
- Meiosis: independent assortment + crossing over reshuffle existing alleles.
- Fertilisation: random combination of gametes → new allele combinations.
- Only mutation creates a genuinely NEW allele.
- Meiosis/fertilisation spread and recombine what already exists.
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.
Module roadmap · mutation → gene pools → biotechnology
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.
What to write in your book
- First half of Module 6 = natural genetic change (mutation, variation, gene pools, populations).
- Second half = biotechnology / deliberate human intervention.
- DNA change → new allele → population fate (rare, lost, or spreads).
- Mutation is the entry point; selection/drift/gene flow decide the fate.
A mutation is random with respect to need. What does natural selection do afterwards?
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."
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."
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].
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 the antibiotic-resistance claim. You should now be able to explain that mutation is random with respect to need, while selection is the process that increases the frequency of a helpful allele after it already exists.