Knowledge Organiser
Part of Variation · GCSE GCSE Biology revision
This topic summary covers Knowledge Organiser within Variation for GCSE Biology. Genetic and environmental variation in organisms It is section 9 of 10 in this topic. Use this topic summary to connect the idea to the wider topic before moving on to questions and flashcards.
Topic position
Section 9 of 10
Practice
25 questions
Recall
20 flashcards
Knowledge Organiser
Key Terms
- Variation — differences between individuals of the same species
- Genetic variation — differences caused by different alleles inherited from parents
- Environmental variation — differences caused by the conditions in which an organism lives or develops
- Continuous variation — a characteristic that shows a range of values with no distinct categories; produces a normal distribution (bell curve); e.g. height, mass
- Discontinuous variation — a characteristic that falls into distinct, separate categories with no intermediate values; e.g. ABO blood group, sex
- Mutation — a random change in the DNA base sequence; the only source of new alleles
- Meiosis — cell division that produces gametes with half the chromosome number; generates genetic variation by random assortment of chromosomes and crossing over between homologous chromosomes
Sources of Variation (3-mark question)
- 1. Mutations — random changes in DNA base sequence; only way new alleles arise in a population
- 2. Sexual reproduction / meiosis — random assortment of chromosomes produces gametes with unique combinations; crossing over between homologous chromosomes shuffles alleles further; random fertilisation adds another layer of variation
- 3. Environment — conditions during development (diet, disease, climate) alter the phenotype without changing the genotype; e.g. diet affects height, UV exposure affects skin colour
- Asexual reproduction produces genetically identical offspring (clones) — no variation except from mutations
Examples
- Continuous: height, mass, foot length, IQ score
- Discontinuous: ABO blood group, tongue rolling, sex
- Purely genetic: blood group, inherited disorders
- Purely environmental: scars, language spoken, tanned skin
- Both genetic and environmental: height, weight, intelligence
- Graph type: continuous → smooth bell curve (histogram); discontinuous → separate bars (bar chart)
Common Marks Lost
- Naming only one or two sources of variation: "explain the causes of variation" questions expect all three — mutations, sexual reproduction/meiosis, and environmental factors; one source alone loses marks
- Saying mutations are always harmful: most mutations are neutral (they occur in non-coding DNA or produce a synonymous codon); harmful mutations are a minority
- Confusing type with cause: continuous/discontinuous describes the pattern of variation; genetic/environmental describes the cause — they are independent categories (blood group is discontinuous AND purely genetic; height is continuous AND both genetic and environmental)
- Not linking variation to natural selection: when variation questions appear alongside evolution questions, add: "variation means some individuals are better adapted and more likely to survive and reproduce"
- Vague meiosis answer: writing "meiosis creates variety" scores 0 — state the specific mechanisms: random assortment of chromosomes AND crossing over between homologous chromosomes
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Practice Questions for Variation
What is the main difference between genetic variation and environmental variation?
Explain how mutations contribute to genetic variation in populations.
Quick Recall Flashcards
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