Edexcel iGCSE Biology-4.34 – 4.37B Mutation & Mutation: Advanced- Study Notes- New Syllabus
Edexcel iGCSE Biology-4.34 – 4.37B Mutation & Mutation: Advanced- Study Notes- New syllabus
Edexcel iGCSE Biology-4.34 – 4.37B Mutation & Mutation: Advanced- Study Notes -Edexcel iGCSE Biology – per latest Syllabus.
Key Concepts:
4.34 understand that mutation is a rare, random change in genetic material that can be inherited
4.35B understand how a change in DNA can affect the phenotype by altering the sequence of amino acids in a protein
4.36B understand how most genetic mutations have no effect on the phenotype, some have a small effect and rarely do they have a significant effect
4.37B understand that the incidence of mutations can be increased by exposure to ionising radiation (for example, gamma rays, x-rays and ultraviolet rays) and some chemical mutagens (for example, chemicals in tobacco)
Mutation – A Source of Genetic Change
🔹 Introduction
Mutation = a rare, random change in genetic material (DNA).
Can occur in any gene or chromosome.
Some mutations can be inherited if they occur in gametes.
📌 Key Points
- Random & rare → cannot be predicted.
- Can be beneficial, neutral, or harmful:
- Beneficial → may help survival (evolution)
- Harmful → may cause disease or abnormality
- Neutral → no noticeable effect
- Inheritance:
- Mutation in body cell → not passed to offspring
- Mutation in gamete → can be inherited
- Examples: Eye colour change (gene mutation), Sickle cell anaemia (harmful, inherited), Antibiotic resistance in bacteria (beneficial)
📊 Summary Table
| Feature | Explanation | Example |
|---|---|---|
| Type | Random change in DNA | Gene or chromosome mutation |
| Frequency | Rare | Spontaneous errors in DNA replication |
| Effect | Beneficial / Harmful / Neutral | Sickle cell anaemia, antibiotic resistance |
| Inheritance | Only if in gametes | Passed to offspring |
📝 Quick Recap
Mutation = rare, random change in DNA.
Inherited only if in gametes.
Can be beneficial, harmful, or neutral.
Source of genetic variation → drives evolution.
DNA Mutation → Protein → Phenotype
🔹 Introduction
Phenotype = observable traits of an organism (e.g., eye colour, height, enzyme function).
Changes in DNA sequence can change amino acids in proteins, which can alter the phenotype.
📌 Key Points
- DNA codes for proteins: Sequence of nucleotides → sequence of amino acids → protein → trait.
- Mutation in DNA: Change in a gene (DNA sequence) → may change amino acid sequence in protein.
Effects:- Non-functional protein → loss of function
- Altered protein function → new trait
- Effect on Phenotype:
- Example 1: Sickle cell anaemia → DNA mutation changes one amino acid in haemoglobin → sickle-shaped RBCs
- Example 2: Albinism → mutation disables enzyme for melanin production → no pigment
📊 Summary Table
| Step | Description | Example |
|---|---|---|
| DNA mutation | Change in nucleotide sequence | A → T substitution |
| Protein sequence change | Alters amino acids | Glutamic acid → Valine |
| Phenotype change | Observable trait affected | Sickle-shaped RBCs, albinism |
📝 Quick Recap
DNA → Amino acids → Protein → Phenotype.
Mutation in DNA → may alter amino acid sequence → can change protein → may affect trait.
Effects can be harmful, beneficial, or neutral.
Key examples: Sickle cell anaemia, albinism.
Effects of Genetic Mutations on Phenotype
🔹 Introduction
Genetic mutations = changes in DNA sequence.
Mutations do not always affect the phenotype.
Their effect depends on where the mutation occurs and what it changes.
📌 Key Points
- Most mutations have no effect: Many occur in non-coding regions or do not change amino acid sequence → called silent mutations.
- Some mutations have a small effect: Minor change in protein → slightly alters function. Usually not harmful, sometimes slightly beneficial.
- Rarely, mutations have a significant effect: Protein function drastically altered → noticeable change in phenotype. Can be harmful (disease) or beneficial (adaptation).
📊 Summary Table
| Effect on Phenotype | Frequency | Example |
|---|---|---|
| No effect | Most mutations | Silent mutation (DNA change but same amino acid) |
| Small effect | Some mutations | Slight enzyme efficiency change |
| Significant effect | Rare mutations | Sickle cell anaemia, antibiotic resistance |
📝 Quick Recap
Most mutations → no effect (silent).
Some mutations → small effect → minor protein/trait changes.
Rare mutations → significant effect → major change in phenotype (harmful or beneficial).
Effect depends on mutation location in DNA and protein change.
Factors Increasing Mutation Rate
🔹 Introduction
Mutation = change in DNA sequence.
Some factors can increase the frequency of mutations → called mutagens.
📌 Key Points
- Ionising Radiation: High-energy radiation damages DNA → mutations.
Examples: Gamma rays, X-rays, Ultraviolet (UV) rays.
Can break DNA strands → incorrect repair → mutation. - Chemical Mutagens: Certain chemicals interact with DNA → change nucleotide sequences.
Examples: Tobacco chemicals (nicotine, tar), industrial chemicals, pesticides.
Can lead to cancer or genetic disorders. - Other Notes: Mutagens do not always cause visible effects immediately.
Some mutations are silent, others harmful.
📊 Summary Table
| Mutagen Type | How it Causes Mutation | Examples |
|---|---|---|
| Ionising radiation | Breaks DNA strands or alters bases | Gamma rays, X-rays, UV rays |
| Chemical mutagens | Changes DNA sequence | Tobacco chemicals, pesticides |
📝 Quick Recap
Mutagens increase mutation rate.
Radiation → DNA strand breaks (gamma, X, UV rays).
Chemicals → DNA sequence changes (tobacco, pesticides).
Mutation effects can be silent, minor, or significant.