Skip to content
Dabour HubLEARN · PRACTICE · EXPLORESign inStudent

2.4.1Unit 2 — Multicellular Organisms

Types of Variation — SQA National 5 Biology Revision Notes & Topical Questions

5 min read 4 parts Lesson 15 of 39

📚 SQA National 5 Biology Hub / Topical Revision
🩺
100% Curriculum Specification Match Lesson Doctor Verified
The only platform with 100% curriculum specification match and verified interactive question banks.
0%read

Part 1 of 4Discrete Variation

2.4.1 Types of Variation
Definition
  • Characteristics that fall into separate, distinct categories with no intermediate values.
Genetic
  • Usually controlled by one gene, so the environment has little or no effect.
Examples
  • Blood groups (A, B, AB, O), and flower colour in pea plants (purple or white).
Graph
  • Shown as a bar chart, because the categories are separate.

Part 2 of 4Continuous Variation

Continuous Variation
Definition
  • Characteristics that show a complete range of values between two extremes.
Genetic
  • Controlled by many genes acting together, called polygenic inheritance.
Environment
  • Often influenced by the environment, such as diet affecting height.
Examples
  • Height, body mass, leaf length and milk yield in cows.
Graph
  • Shown as a histogram or line graph, and many measurements give a bell-shaped curve.
FeatureDiscreteContinuous
Number of genesOneMany
CategoriesDistinctRange of values
Environmental effectLittle or noneOften significant
GraphBar chartHistogram or line

Part 3 of 4Causes of Variation

1
Variation between individuals of the same species results from genes inherited from two parents.
2
Each parent produces gametes with different combinations of genes, and fertilisation is random.
3
The environment then influences how the genes are expressed, for example nutrition affecting growth.
4
Because of both effects, no two individuals other than identical twins are genetically the same.
5
Variation is important because it gives a species the ability to survive when conditions change.

Part 4 of 4Exam Checklist & Tips

2.4.1 – Key Points for the Exam

  • Variation Differences in characteristics between individuals of the same species.
  • Discrete variation Variation in distinct categories, controlled by a single gene.
  • Continuous variation Variation in a range of values, controlled by many genes.
  • Polygenic Controlled by many genes.
  • Phenotype The observable characteristics of an organism.

Common Mistakes

  • Using a line graph for blood groups; it needs a bar chart.
  • Saying continuous variation is caused only by the environment; genes play a major part.
  • Stating that environment can change discrete characteristics such as blood group.
  • Describing discrete variation as having an intermediate form, such as pale purple.

Last updated:

\n