18.1

Variation

Cambridge IGCSE Biology (0610)  · Unit 18: Variation and selection  · 12 flashcards

Variation is topic 18.1 in the Cambridge IGCSE Biology (0610) syllabus , positioned in Unit 18 — Variation and selection , alongside Adaptive features and Selection.  In one line: Variation refers to the differences between individuals of the same species. These differences can be in physical traits (phenotype) or genetic makeup (genotype).

This topic is examined in Paper 1 (multiple-choice) and Papers 3/4 (theory), plus Paper 5 or Paper 6 (practical / alternative to practical). Past papers from 2022 to 2025 record 3 explicit questions on this topic — though the concept underpins many adjacent topics, so it is tested far more often than that figure suggests.

The deck below contains 12 flashcards — 3 definitions, 7 key concepts and 2 application cards — covering the precise wording mark schemes reward.  Use the 3 definition cards to lock down command-word answers (define, state), then move on to the concept and application cards to handle explain, describe and compare questions.

Key definition

'variation' in the context of biology

Variation refers to the differences between individuals of the same species. These differences can be in physical traits (phenotype) or genetic makeup (genotype).

Example: Differences in height among humans.

What the Cambridge 0610 syllabus says

2026-2028 syllabus, in our words

What the syllabus expects you to be able to do in this topic, in plain English. Match the command word (Describe, Explain, State, etc.) in your answer to score full marks. For the exact wording, see the official syllabus (PDF).

  1. Describe Describe variation as the differences between individuals of one species.
  2. State State that continuous variation gives a range of phenotypes lying between two extremes, for example body length and body mass.
  3. State State that discontinuous variation produces only a few distinct phenotypes, with no in-between forms, for example ABO blood groups and the shape and colour of pea seeds.
  4. State State that genes alone usually cause discontinuous variation, while continuous variation results from both the environment and genes.
  5. Investigate Investigate examples of both discontinuous and continuous variation, and describe them.
  6. Describe Describe mutation as a change to the genetic material.
  7. State State that new alleles arise through mutation.
  8. State State that the mutation rate is increased by ionising radiation and by some chemicals.
  9. Describe Describe gene mutation: a change in the order of bases in DNA that happens at random. Supplement
  10. State State that a population's genetic variation can arise from mutation, from meiosis, from random mating and from random fertilisation. Supplement
Definition Flip

Define 'variation' in the context of biology.

Answer Flip

Variation refers to the differences between individuals of the same species. These differences can be in physical traits (phenotype) or genetic makeup (genotype).

Example: Differences in height among humans.
Key Concept Flip

What is continuous variation, and provide an example.

Answer Flip

Continuous variation results in a range of phenotypes between two extremes. It is usually caused by the interaction of multiple genes and environmental factors.

Example: Human body length, which varies across a spectrum of heights.
Key Concept Flip

What is discontinuous variation, and provide an example.

Answer Flip

Discontinuous variation results in a limited number of distinct phenotypes with no intermediates. It is usually caused by a single gene or a small number of genes.

Example: ABO blood groups in humans, where individuals have distinct blood types (A, B, AB, or O).
Key Concept Flip

What factors cause continuous variation?

Answer Flip

Continuous variation is caused by a combination of genetic factors (multiple genes) and environmental influences. This interaction results in a range of phenotypes.

Example: Height in pea plants is affected by both genes for growth and access to sunlight/nutrients.
Key Concept Flip

What factors cause discontinuous variation?

Answer Flip

Discontinuous variation is primarily caused by genes alone, typically involving a single gene or a small number of genes with distinct alleles. Environmental factors have little to no impact.

Example: Seed color in peas (yellow or green) determined by a single gene.
Definition Flip

Define 'mutation' in genetics.

Answer Flip

Mutation is a change in the genetic material (DNA) of an organism. It can be a change in a single base pair or a larger alteration affecting multiple genes.

Example: A point mutation in the gene for hemoglobin can cause sickle cell anemia.
Key Concept Flip

How do mutations contribute to genetic variation?

Answer Flip

Mutation is the primary way in which new alleles (versions of a gene) are formed. These new alleles can then lead to new phenotypes, increasing the genetic variation within a population.

Example: A mutation in a flower color gene leading to a new flower color.
Key Concept Flip

What environmental factors can increase the rate of mutation?

Answer Flip

Ionising radiation (e.g., X-rays, UV radiation) and certain chemicals (mutagens) can increase the rate of mutation in cells. These agents damage DNA, leading to errors during replication.

Example: Exposure to UV radiation can cause mutations in skin cells, leading to skin cancer.
Definition Flip

Describe gene mutation at the molecular level.

Answer Flip

Gene mutation is a random change in the base sequence of DNA. This can involve the substitution, insertion, or deletion of one or more nucleotides.

Example: A substitution mutation changes one base pair, like changing adenine to guanine.
Key Concept Flip

Besides mutation, what other processes are sources of genetic variation in populations?

Answer Flip

Meiosis (crossing over and independent assortment), random mating, and random fertilization are additional sources of genetic variation. These processes shuffle and combine existing alleles in new ways.

Example: Crossing over during meiosis in gamete formation.
Key Concept Flip

Give an example of a human trait exhibiting continuous variation, and explain why it is continuous.

Answer Flip

Human height is an example of continuous variation. It is continuous because it is influenced by multiple genes (polygenic inheritance) and environmental factors like nutrition, resulting in a wide range of heights in the population.

Key Concept Flip

Give an example of a human trait exhibiting discontinuous variation, and explain why it is discontinuous.

Answer Flip

The ability to roll one's tongue is an example of discontinuous variation. Either you can roll your tongue or you cannot, and this trait is largely determined by a single gene with two alleles, leading to distinct phenotypes.

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17.4 Monohybrid inheritance 18.2 Adaptive features

Key Questions: Variation

Define 'variation' in the context of biology.

Variation refers to the differences between individuals of the same species. These differences can be in physical traits (phenotype) or genetic makeup (genotype).

Example: Differences in height among humans.
Define 'mutation' in genetics.

Mutation is a change in the genetic material (DNA) of an organism. It can be a change in a single base pair or a larger alteration affecting multiple genes.

Example: A point mutation in the gene for hemoglobin can cause sickle cell anemia.
Describe gene mutation at the molecular level.

Gene mutation is a random change in the base sequence of DNA. This can involve the substitution, insertion, or deletion of one or more nucleotides.

Example: A substitution mutation changes one base pair, like changing adenine to guanine.

Tips to avoid common mistakes in Variation

More topics in Unit 18 — Variation and selection

Variation sits alongside these Biology decks in the same syllabus unit. Each uses the same spaced-repetition system, so progress in one informs the next.

18.2 Adaptive features

9 flashcards
18.3 Selection

12 flashcards

Cambridge syllabus keywords to use in your answers

These are the official Cambridge 0610 terms tagged to this section. Mark schemes credit responses that use the exact term — weave them into your answers verbatim rather than paraphrasing.

variation continuous variation discontinuous variation genetic variation environmental variation mutation gene mutation chromosome mutation

Key terms covered in this Variation deck

Every term below is defined in the flashcards above. Use the list as a quick recall test before your exam — if you can't define one of these in your own words, flip back to that card.

'variation' in the context of biology
'mutation' in genetics
Describe gene mutation at the molecular level

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