CIE iGCSE Co-ordinated Sciences-B17.1 Variation- Study Notes- New Syllabus
CIE iGCSE Co-ordinated Sciences-B17.1 Variation – Study Notes
CIE iGCSE Co-ordinated Sciences-B17.1 Variation – Study Notes -CIE iGCSE Co-ordinated Sciences – per latest Syllabus.
Key Concepts:
Core
Describe variation as differences between individuals of the same species
State that continuous variation results in a range of phenotypes between two extremes; examples include body length
State that discontinuous variation results in a limited number of phenotypes with no intermediates; examples include ABO blood groups
Describe mutation as a genetic change
State that mutation is the way in which new alleles are formed
CIE iGCSE Co-Ordinated Sciences-Concise Summary Notes- All Topics
Variation
📌 Definition
Variation = differences between individuals of the same species.
🌱 Key Points
- Variation makes each individual unique.
- Can affect physical traits, behaviour, or physiology.
- Two main types:
- Continuous variation – shows a range of values (e.g., height, weight)
- Discontinuous variation – falls into distinct categories (e.g., blood group, eye colour)
- Causes of variation:
- Genetic factors → differences in alleles inherited from parents
- Environmental factors → nutrition, temperature, lifestyle
📊 Summary Table
| Type | Description | Example |
|---|---|---|
| Continuous | Range of values, measured | Height, weight |
| Discontinuous | Distinct categories, not a range | Blood group, tongue rolling |
| Causes | Genetic & environmental | Genes, diet, climate |
⚡ Quick Recap
Variation = differences within a species
Memory tip: “Same species, different traits → that’s variation!”
Continuous Variation
📌 Definition
Continuous variation is the gradual range of differences in a trait between two extremes in a species.
🔑 Key Features
- Range of Phenotypes
Traits show a spectrum, not distinct categories.
Example: body length, height, weight, leaf length. - Quantitative Measurement
Measured using numbers (cm, kg, etc.).
Data often plotted as a bell-shaped curve. - Causes
Genetic factors → alleles inherited from parents.
Environmental factors → nutrition, temperature, lifestyle.
📊 Summary Table
| Feature | Description | Example |
|---|---|---|
| Variation type | Continuous | Height, body length, weight |
| Phenotypes | Range between two extremes | Short ↔ Tall |
| Measurement | Quantitative | cm, kg |
| Cause | Genetic + Environmental | Genes + nutrition |
⚡ Quick Recap
Continuous variation = gradual differences in traits
Memory tip: “From one extreme to the other, with many possibilities in between.”
Often shown as a bell curve in diagrams.
Discontinuous Variation
📌 Definition
Discontinuous variation results in a limited number of distinct phenotypes with no intermediates.
🔑 Key Features
- Distinct Categories
Traits fall into clear, separate groups.
There are no gradual differences or intermediate forms. - Examples
ABO blood groups (A, B, AB, O)
Tongue rolling (can or cannot roll)
Eye colour categories (simplified) - Causes
Mainly genetic factors.
Environmental influence is minimal.
📊 Summary Table
| Feature | Description | Example |
|---|---|---|
| Variation type | Discontinuous | ABO blood groups |
| Phenotypes | Limited, distinct, no intermediates | A, B, AB, O |
| Cause | Mostly genetic | Alleles of a single gene |
⚡ Quick Recap
Discontinuous variation = distinct categories, no in-between
Memory tip: “Clear-cut traits → each person fits a box.”
Mutation
📌 Definition
Mutation = a change in the genetic material (DNA) of an organism.
🌱 Key Points
- Can occur spontaneously or be induced by environmental factors (mutagens like radiation or chemicals).
- Can affect a single gene (point mutation) or whole chromosomes (chromosomal mutation).
- Can lead to new alleles, which may cause:
- Beneficial traits → evolution
- Harmful traits → disease or reduced survival
- Neutral effects → no noticeable change
📊 Summary Table
| Feature | Description | Example |
|---|---|---|
| Type | Genetic change | DNA sequence alteration |
| Cause | Spontaneous or induced | Radiation, chemicals |
| Effect | New alleles; may be beneficial, harmful, or neutral | Sickle cell allele (harmful), antibiotic resistance in bacteria (beneficial) |
⚡ Quick Recap
Mutation = change in DNA
Memory tip: “DNA changes → new alleles → evolution or disease.”
Mutation and Allele Formation
📌 Key Statement
Mutations are the way in which new alleles are formed.
🌱 Key Points
- Alleles = different versions of a gene.
- When a gene mutates, its DNA sequence changes → new allele arises.
- New alleles may cause:
- Beneficial traits → increase survival or reproduction
- Harmful traits → may reduce survival
- Neutral traits → no noticeable effect
📊 Summary Table
| Feature | Description | Example |
|---|---|---|
| Process | Mutation | DNA sequence change |
| Outcome | Formation of new alleles | Sickle cell allele, antibiotic resistance |
| Effect | Beneficial, harmful, or neutral | Depends on environment and trait |
⚡ Quick Recap
Mutation = source of new alleles
Memory tip: “DNA changes → new allele → potential for evolution.”