# Variation and Mutation
No two organisms are exactly alike (except identical twins). Variation within a species arises from genetic differences, environmental factors, or both. Mutations are the ultimate source of new genetic variation.
1. Types of Variation
Genetic Variation
- Caused by differences in DNA
- Inherited from parents
- Examples: blood group, eye colour, attached/free earlobes
Environmental Variation
- Caused by conditions the organism lives in
- NOT inherited
- Examples: scars, accent, tan
Both
- Many characteristics influenced by BOTH genes and environment
- Examples: height (genes set potential, nutrition determines actual), weight, skin colour
2. Continuous vs Discontinuous Variation
| Continuous | Discontinuous |
|---|---|
| Range of values | Distinct categories |
| Influenced by many genes + environment | Usually one or few genes |
| Examples: height, mass, foot length | Examples: blood group, tongue rolling |
| Shown on a histogram/line graph (bell curve) | Shown on a bar chart |
3. Mutations
A change in the DNA base sequence.
Causes:
- Spontaneous errors during DNA replication
- Mutagens: UV radiation, X-rays, certain chemicals, ionising radiation
Effects:
- Most mutations: no effect (occur in non-coding DNA or produce same protein)
- Some harmful: sickle cell disease, cancer
- Rarely beneficial: antibiotic resistance in bacteria; better camouflage
4. Mutations and Evolution
Beneficial mutations → natural selection → spread through population.
Example: bacteria with mutation for antibiotic resistance survive when others die → resistant population.
5. Sources of Genetic Variation
- Mutation: creates new alleles
- Meiosis: independent assortment and crossing over shuffle alleles
- Sexual reproduction: combines alleles from two parents (fertilisation)
6. Practice Questions
- Give two examples each of genetic and environmental variation.
- Explain the difference between continuous and discontinuous variation.
- What is a mutation?
- Explain how a mutation can lead to antibiotic resistance in bacteria.
- Why does sexual reproduction produce more variation than asexual reproduction?
Want to check your answers and get step-by-step solutions?
Summary
- Variation: genetic, environmental, or both
- Continuous (range) vs discontinuous (categories)
- Mutations: changes in DNA; most harmless; some beneficial/harmful
- Genetic variation sources: mutation, meiosis, sexual reproduction
- Beneficial mutations drive evolution via natural selection