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.
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Mutation Alleles
Think First
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.
Mutation introduces genuinely new genetic information
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.
Overview of mutation as the ultimate source of genetic change
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.
Gene, allele and gene pool are related but not interchangeable
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.
Meiosis and fertilisation reshuffle variation already present
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.
Natural genetic change and human-induced genetic change are different layers of the module
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.
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.
Look back at what you wrote in the Think First section. What has changed? What did you get right? What surprised you?
Activities
Activity 1 - New allele or reshuffled allele?
For each scenario, decide whether the source of variation is mainly mutation, meiosis/fertilisation reshuffling, or selection changing frequency after the fact.
1. A base in a pigment gene changes, producing a new coat-colour allele.
2. Two siblings inherit different combinations of the same parental alleles.
3. A resistant bacterial strain becomes common after antibiotic use.
4. A child inherits one maternal allele and one paternal allele for a gene.
Activity 2 - Population language repair
Rewrite each flawed statement using accurate HSC biology terminology.
1. "The environment made the mutation happen so the species could adapt."
2. "Fertilisation creates new alleles every generation."
3. "A gene pool is all the genes inside one organism."
Multiple Choice
1. Which process is the direct source of a new allele in a population?
2. Which statement best defines a gene pool?
3. Two parents produce offspring with different combinations of the same alleles they already carry. This variation is mainly produced by
4. Which statement correctly links mutation and natural selection?
5. Why is it important to separate natural genetic change from human-induced genetic change at the start of Module 6?
Short Answer
6. Define mutation, allele and gene pool, then explain how they are linked. 3 marks
7. Compare the roles of mutation, meiosis and fertilisation in producing genetic variation. 4 marks
8. Evaluate the statement: "Antibiotics cause bacteria to mutate so they can survive." Use the antibiotic resistance anchor in your answer. 5 marks